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Chapter 7 THE EVOLUTION OF BIODIVERSITY On a scale of millions of years extinction adaptation speciation climate change and geological change create different assemblages of specie ESTIMATING CHANGES IN TAXONOMIC DIVERSITY ESTIMATES OF DIVERSITY Geological periods and stages vary in duration and more recent geological times are represented by greater volumes and areas of fossiliferous rock The duration of a taxon is measured by determining its rst and last appearance in the fossil record The duration of a taxon is imprecise the actual times of originating and eXtinction of a taxon may have occurred earlier and later of the apparent times of origin and eXtinction Our count of living recent species is much more complete than our count of past species EXtant taxa have apparently longer durations and lower eXtinction rates than they would if they had been recorded only as fossils Diversity seems to increase as we approach the present Pull of the Recent RATES The rate of change in diversity depends on the rates at which taxa originate and become eXtinct The number of taxa N changes over time by origination and eXtinction These events are analogous to the births or deaths of individual organisms in a population Models of population growth can be adapted to describe changes in taxonomic diversity N the number of taxa S the number of originations per original taxon in the time interval E the number of eXtinctions per original taxon in the time interval AN the change in N equals the number of births minus the number of deaths At the time interval SN AN the change in N due to births EN AN the change in N due to deaths The diversi cation rate is rate if change in diversity It is calculated by the formula below M SNEN or M RN At At Where R is the per capita rate ofincrease R SE If R gt 1 the growth number of taxa is positive A population grows in a time interval beginning at to and ending at t1 by multiplying the original size of the population No by the per capita rate of increase R N1 NOR If S and E remain constant then the population will be at the end of the next interval N2 NIR NOR2 In general after t time intervals the number of taxa will be N NORt For continuous growth rather than growth in discrete intervals Population size at various times during exponential growth can be projected with the formula N Naequot N number at time t N7 number at time 0 e base ofnatural log 271828 t period oftime being studied r biotic potential or instantaneous per capita rate of increase Exponential growth rate IN N number of individuals dt r biotic potential or instantaneous per capita rate of increase t time Exponential growth is not realistic No population can grow inde nitely There are limitations presented by the environment food space etc and competition for available resources increases These are called density dependent factors Increased density eventually increases mortality decreases fecundity and causes emigration Logistic growth or sigmoid growth is exponential at rst then growth begins to slow down until it reaches zero when births balance deaths Slow fast slow zero growth Environmental resistance modi es growth Sshaped curve It represents how populations respond to density The biotic potential and size of the population modi ed by the environmental resistance determine the growth rate Environmental resistance refers to the limitations placed on the biotic potential due to unfavorable 39 conditions eg 39 39 predation Carrying capacity is the maximum number of individuals an area can support K The density of organisms is in equilibrium with the source supply the environment U 39 quot can be 39 39 39 to a l l 39 since 1 39 between members may be necessary rN K N1 N number of individuals 611 instantaneous rate of change dt K r biotic potential dt t time K carrying capacity K N it is a measure of the environmental resistance or the effect of crowding K this represents the opportunity for further population growth As the population grows this unutilized opportunity declines This expression slows population growth When N is small K NK is close to 1 As N increases and approaches K the value of the expression decreases towards 0 If N gt K then dNdt is negative and the population N decreases toward K Logistic growth curve is theoretical It is a mathematical model of how populations grow under favorable conditions Natural populations although they appear to grow logistically they rarely do Some reasons for this difference age structure may not be stable immigration or emigration birth and death rate changed Exponential growth is not realistic No population can grow inde nitely There are limitations presented by the environment food space etc and competition for available resources increases Increased density eventually increases mortality decreases fecundity and causes emigration Logistic growth or sigmoid growth is exponential at rst then growth begins to slow down until it reaches zero when births balance deaths Slow fast slow zero growth Environmental resistance modi es growth Sshaped curve It represents how populations respond to density The biotic potential and size of the population modi ed by the environmental resistance determine the growth rate Environmental resistance refers to the limitations placed on the biotic potential due to unfavorable 39 39 conditions eg 39 39 predation Carrying capacity is the maximum number of individuals an area can support K The density of organisms is in equilibrium with the source supply the environment I U39 quot canbe39 39 39toa 39 be necessary since 1 39 between members may 1 1 rN 1K N N number of individuals 611 instantaneous rate of change dt K r biotic potential dt t time K carrying capacity K N2 it is a measure of the environmental resistance or the effect of crowding K this represents the opportunity for further population growth As the population grows this unutilized opportunity declines This eXpression slows population growth When N is small K NK is close to 1 As N increases and approaches K the value of the eXpression decreases towards 0 If N gt K then dNdt is negative and the population N decreases toward K Logistic growth curve is theoretical It is a mathematical model of how populations grow under favorable conditions Natural populations although they appear to grow logistically they rarely do Some reasons for this difference age structure may not be stable immigration or emigration birth and death rate changed Walker Valentine Model An ecosystem may have a stable equilibrium number of species that is less than the maXimal possible number 0 It assumes that the rate of eXtinction E is independent of the diversity 0 The per species rate of origination of new species S declines as the number of species N approaches the maXimum Nmax that the environment can support 0 S0 is the highest possible rate of speciation SSo1N Nmax The rate of change in the number of species is M S 7 EN S0 l 7 N 7 E N See page 142 for the formulas At max When M 0 the equilibrium number of species Nquot is Nquot l 7 E Nmax At S0 See graph 72 o S is greatest at intermediate diversity because it increases with the number of potential ancestors but declines at high diversity levels dropping to zero at the maXimal number of species the resources can sustain Nmax o The number of eXtinctions is greater per unit of time if there are more species 0 The number of species reaches equilibrium when S E when speciation and eXtinction are equal TAXONOMIC DIVERSITY THROUGH THE PHANEROZJOIC EON The most complete fossil recor4d has been left by marine animals with hard parts shells or skeletons Jack Sepkoski 1984 1993 compiled data on the stratigraphic ranges of more than 4000 marine families and 20000 general throughout the 542 Mya of the Phanerozoic His plot shows Rapid increase in the Cambrian and Ordovician A plateau throughout the rest of the Paleozoic A steady increase throughout the Mesozoic and Cenozoic Diversity reaching its peak in the Tertiary This pattern is interrupted by mass extinctions On land diversity has also increased 0 Number of families of insects shows a steady increase since the Permian o Flowering plants birds and mammals have also steadily increased RATES OF ORIGINATION AND EXTINCTION There were episodes when an exceptionally high number of taxa became extinct are called mass extinctions Times when the number of extinctions occur at more gradual rate are referred to as background extinctions Biodiversity in marine species has increased during the Mesozoic and Cenozoic due to an increase in otiginations since the Triassic The rate of origination of new families was highest in animal evolution in the Cambrian and Ordovician and in the early Triassic after the great Permian extinction Five mass extinctions are generally recognized I Ordovician N440 million years ago 50 of animal families including many trilobites 2 Devonian N360 million years ago 30 of animal families including agnathans and placoderm shes and many trilobites 3 Permian 240 million years ago 50 of the marine families 90 of the marine species Many trees amphibians most brachiopods and bryozoans all trilobites 4 Triassic 180 million years ago 35 of the families including many reptiles and ammonoids 5 Cretaceous 65 million years ago Dinosaurs many foraminiferans ammonites Taxa with high rate of origination also have a high rate of extinction Possible reasons for this correlation are 0 Degree of ecological specialization Specialized species are likely to be more vulnerable than generalists 0 Species with low or uctuating population sizes are susceptible to eXtinction Some authors believe that small population enhance speciation this idea is controversial 0 Geographic range Species with broad geographic range tend to have a lower risk of eXtinction because they entire species is not found in one locality where a localized environmental change would have a great effect A study conducted by Foote 2000 showed that biodiversity 0 Increased when the rate of origination increased 0 Decreased when the rate of eXtinction increased 0 Extinction had a stronger effect on biodiversity than did origination in the Paleozoic o Origination had a stronger effect during the Mesozoic and Cenozoic CAUSES OF EXTINCTION Extinction is caused by the failure of a species to adapt to changes in its environment When the environment deteriorates populations become eXtinct and the range of the species contracts Declining populations depend on adaptive genetic changes to survive The survival of the population will depend on how rapid is the environmental change relative to the rate at which characters evolve The rate of evolution may depend on the rate at which mutation supplies genetic variation and on population size because small populations will eXperience fewer mutations o A change that reduces population size reduces the chances of adapting to it The change in one environmental factor may bring about changes in other factors and the survival of a species may require evolutionary change in several or many features 0 A change in temperature may cause a change in species composition of a community DECLINING EXTINCTION RATES Natural selection has no foresight and cannot prepare species for changes in the environment At any given time t the probability of eXtinction of a species or higher taxon would be the same whether it is old arose long before t or young arose shortly before t Studies show that the probability of eXtinction is roughly constant because organisms are continually assaulted by new environmental changes each carrying the risk of eXtinction As other taxa evolve the environment of an organism deteriorates and it must constantly evolve to survive Background extinction has declined over time o This may be the result of the increase in the average number of species per family eg a large family will take longer to become extinct than a smaller one 0 Higher taxa that were more prone to extinction were eliminated early in the Phanerozoic MASS EXTINCTIONS Of the ve mass extinctions generally recognized the one at the end of the Permian was the most severe eliminating about 54 of the marine families and 90 of the species 0 On land several orders f insects became extinct and the dominant amphibian and therapsids were replaced by new groups of therapsids that eventually gave rise to mammals and dinosaurs The second most severe mass extinction in terms of taxa affected occurred at the end of the Ordovician b between 440450 mya 0 Over 100 families disappeared The end of the Cretaceous extinction KT eliminated the dinosaurs it occurred about 65 mya httpparkorg 4 extincti 39 html Causes of mass extinctions Most paleontologists agree that the cause of the KT extinction was the impact of an asteroid o The Chicxulub crater off the coast of Yucatan is the prime suspect 0 Proposed by Alvarez et al Some scientists think that there were other causes because the extinction of various taxa was too spread out in time to be caused by one catastrophe Several causes have been proposed for the extinction at the end of the Permian o Volcanic eruption that produced the Siberian Traps The eruptions caused a global warming that depleted the oceans of oxygen by altering oceanic currents 0 Global warming may have caused the release of large amount of methane that further enhanced warming in a positive feedback spiral Victims survivors and consequences Extinctions exerted a selective pressure by eliminating some taxa and allowing others to survive Species of gastropods with wide range and ecological distribution and genera with many species survived etter Extinctions appear to have been random with respect to other characteristics such as mode of feeding The same pattern appears to be the same in periods of background extinctions These characteristics correlated with survival seem to be different from those that allowed survival at the end of the Cretaceous Physical and environmental conditions were probably very different after mass extinctions than before This appears to be the reason for the diversi cation of some taxa after the extinction and the slow dwindling of other taxa According to Stephen J Gould there are tiers of evolutionary change that must be understood in order to comprehend the full history of evolution 1 Microevolutionary change within the population and species 2 Differential proliferation and extinction of species during normal geological times which affect the relative diversity of lineages 3 The shaping of the biota by mass extinctions which can eliminate diverse taxa and reset the stage for new evolutionary radiations initiating evolutionary histories that are largely decoupled from earlier ones The extinction of one group permitted the ourishing of others allowing the emergence of new community structures ORIGINATION AND DIVERSIFICATION The major factors that have promoted diversi cation are Release from competition Ecological divergence Coevolution Provinciality Release from competition Lineages diversify rapidly when they are presented with vacant niches o E g Adaptive radiation of cichlid shes in the Great Lakes of Africa the nches in the Galapagos and the honeycreepers of Hawaii Competition may play the important role There are two hypotheses 1 Competitive displacement the younger group caused the extinction of the older group 2 Incumbent replacement the extinction of the older taxon allowed the younger taxon to radiate Both seem to have played a role How competition has affected diversity remains controversial Competitive displacement requires that The two taxa lived in the same locality at the same time Competed for the same resources The older taxon was not decimated by an extinction event The diversity and abundance of the younger taxon increased as the older taxon decreased It probably rarely occurred Incumbent replacement Probably more common The radiation of groups only after the older taxa had disappeared Extinction and radiation occurred in different places and times All these support the release from competition Ecological Divergence Key adaptation an adaptation that allows an organism to occupy a new ecological niche often by using a novel resource or habitat o It implies the diversi cation of the group An adaptive zone is a set ofecological niches occupied by a group of species a higher taxon Insectivorous bats that are nocturnal occupy a zone different from that of diurnal bats It includes all nocturnal bats that belong to different genera and families but belong to the same order Chiroptera I represent an ecological pathway along which a taxon evolves At the species level is the same as the fundamental niche A set of adaptive zones is called an ecological space Expansion into new habitats and feeding habits accounts for the diversi cation of most families of tetrapod vertebrates such as frogs snakes and birds Applying the method of Replicated SisterGroup Comparison gives support to the hypothesis that moving into new underutilized niches increases diversi cation Involves the comparison of sister clades that retain the ancestral character with those that have new adaptation o E g herbivorous beetles are more diverse than their sister taxa that retain the ancestral character of feeding on detritus fungi or animals 0 Phylogenetic studies have to identify the ancestral and the evolved characters The partitioning of ecological niches has contributed to the diversi cation of species Related species reduce competition by subtle differences in resource utilization 7 occupation of microhabitats eg warblers feeding at different levels on the same tree Coevolution The diversi cation of one group can support the diversi cation of another group Eg there are about 755 species of gs worldwide which are pollinated by over a 1000 species of g wasps that are in turn parasitized by a similar number of species speci c nematodes Fig wasps are circumtropical in distribution with about 640 described species in the world This gure probably represents about 2030 of the eXisting species The relationship of the pollinating g wasps with their host g tree is an obligate mutualism the tree relies on the wasps for pollen dispersal and pollination and in turn the wasps can only reproduce in the orets within the g A very interesting site httpwww cweb orgFigs and g 39 39 htm Provinciality The division of biota among geographic regions is called provinciality A trend from a cosmopolitan distribution of taxa to more localized distributions has persisted throughout much of the Mesozoic and Cenozoic The separation of the land masses during the Mesozoic and Cenozoic over a greater latitudinal variation has increased the diversity of habitats and climatic conditions 0 Land masses spread almost from pole to pole 0 Two disjunct oceans were created the Atlantic and the IndoPaci c Oceans o Fragmentation of land masses prevented the interchange of species and increased isolation The Role of Environmental Change Changes in climate have been associated with changes in the distribution of habitats and vegetation types which in turn have facilitated major changes in the distributions taxa often leading to diversi cation Changes in temperature seem unrelated to origination rate in mammals in the Tertiary although some of them match declines in diversity Chapter 1 EVOLUTIONARY BIOLOGY WHAT IS EVOLUTION The word evolution comes from the Latin word evolvere which means to unfold or unroll To reveal the hidden potentialities It has come to mean change Biological evolution refers to the change in the characteristics of groups of organisms over many generations over time The development or ontogeny of an individual organism is not considered evolution 0 Individual organisms do not evolve o Populations of organisms evolve they undergo descent with modi cation Changes that are passed from one generation to the next are considered evolutionary these are genetic changes 0 The resurgence of antibiotic resistant diseases is an example of natural selection BE FORE DARW IN Darwin s theory of biological evolution revolutionized the prevailing worldview in the West that had existed from the time of Plato and Aristotle Plato 428348 B C Greek Philosopher Idea or form is real and everything else is a re ection of this reality The essence or idea is imperfectly imitated by its earthly representations The real world is the world of ideas and what we see on earth is only an imitation of those ideas The essence or form of a structure could be understood from its function since the function dictated the form Species became the initial mold for all later replicates of that species 0 Theory of essentialism Aristotle 384322 B C Greek philosopher Aristotle developed the Plato s concept of immutable essence into the notion that species have xed properties Aristotle proposed that the last stage of development the adult form explains the changes that occur in the immature forms teleological explanation the advanced stages in uence the earlier stages He also proposed that all living forms are linked in a progression from imperfect to most perfect He called this the Scale ofNature Christian thought elaborated on Platonic and Aristotelian philosophy that existence is good and the God s benevolence is complete therefore He must have bestowed existence on every creature giving each its own essence Since order is superior to disorder God s creation must follow a plan especially a gradation from imperfect to perfect o Inanimate objects to plants to invertebrates up to vertebrates human and nally angels o Scala Naturae or Scale of Nature or the Great Chain of Being The Principle of Plenitude The legacy of Plato to European thinking about the natural world has been expressed as the Principle of Plenitude Lovejoy 193639 Rolfe 1985 This was the belief that all possible kinds of things exist in the world already and nothing more can be created Aristotle39s legacy was more complicated but has been summarized by Rolfe as the concept of continuity and gradation between adjacent kinds of being when hierarchically arranged 1985 p 300 Together the Principle of Plenitude and the Great Chain of Being led to the belief from medieval times that a continuous chain extended from the inanimate world of nonliving matter such as earth and stones through the animate world of plants zoophytes and the lowest forms of animal life upwards to the quadrupeds and eventually through Man to the realms of angels and nally to the Christian God This belief also entailed the View that just as nothing new could be created neither could anything be exterrninated since this would counteract the will of God Rolfe 1985 p 10 http www ndarticlescomparticlesmi m2267is n3 v62ai 17909868pg 4 Aristotle the Scale of Nature and modern attitudes to animals In the Company of Animals Social Research Fall 1995 by Juliet CluttonBrock Linnaeus Carolus 170778 Swedish botanist and taxonomist Linnaeus is considered the founder of the binomial system of nomenclature and the originator of modern scienti c classi cation of plants and animals He used the species as the basic unit in building his system upward to larger categories He grouped related species into genera and related genera into orders and so on In his mind this species had been related in the mind of the Creator Hutton James 172697 Scottish geologist Hutton formulated controversial theories of the origin of the earth in 1785 He was of the opinion that the earth must be very old 0 Uniformitarianism the doctrine that past geological changes in the earth were brought about by the same causes as those now taking place It stressed the slowness and gradualness of rates of change Lyell Sir Charles 17971875 English geologist Lyell argued in his book that at the time presently observable geological processes were adequate to explain geological history He thought the action of the rain sea volcanoes and earthquakes explained the geological history of more ancient times Lyell conclusively showed that the earth was very old and had changed its form slowly mainly from conditions such as erosion Lyell was able to date the ages of rocks by using fossils embedded in the stone as time indicators Lyell helped win acceptance of James Hutton s theory of uniformitarianism and of Charles Darwin s theory of evolution Lamarck Jean Baptiste Pierre Antoine de Monet Chevalier de 17441829 Lamarck was born in Bazentin lePetit France Sent to a Jesuit school in Arniens He received a classical education until 1759 That year his father died and Lamarck entered the military and began to study plants In 1768 he left military service and studied medicine in Paris for four years during which time he became interested in meteorology chemistry and shell collecting Lamarck was elected to the Academy of Sciences and became an associate botanist in 1783 His most signi cant work was done when he began to work at the Jardin du Roi King s Garden in 1788 When the garden was reorganized in 1793 Lamarck s ideas helped to frame the structure of the new Museum of Natural History He became professor of insects and worms in the Museum of Natural History a division he named invertebrate zoology Lamarck s theoretical observations on evolution referred to in the early 19th century as transformism or transmutation preceded his extensive observational work on invertebrates Lamarck accepted the View that animals in nature were arranged on one continuous quotscala naturaequot First biologist to actively propose evolution Lamarck died with little scienti c recognition of his work or his ideas Not until the second half of the 19th century were Lamarck s ideas seriously considered again LAMARCKISM Lamarck proposed the principle of the inheritance ofacquired characteristics Lamarck based his theory of evolution in part on his study of the fossils of marine invertebrates was that species do change over time He believed furthermore that animals evolve because unfavorable conditions produce needs that animals try to satisfy Species not only become extinct but also undergo a gradual modi cation through time Organisms have an inner perfecting principle that 0 could sense the needs of the environment 0 respond by developing adaptations o mostly from simple to compleX Their environment does not passively alter organisms A change in the environment causes changes in the needs of organisms living in that environment which in turn causes changes in their behavior Two mechanisms are involved in evolution o Principle of use and disuse o Inheritance of acquired characters Lamarck viewed evolution as a process of increasing complexity and quotperfectionquot not driven by chance 0 quotNature in producing in succession every species of animal and beginning with the least perfect or simplest to end her work with the most perfect has gradually complicated their structurequot Philosophie zoologique While the mechanism of Lamarckian evolution is quite different from that proposed by Darwin the predicted result is the same adaptive change in lineages ultimately driven by environmental change over long periods of time Lamarck did not believe in extinction for him species that disappeared did so because they evolved into different species Lamarck s Philosophie zoologique mentions the great variety of animal and plant forms produced under human cultivation Lamarck even anticipated Darwin in mentioning fantail pigeons the presence of vestigial nonfunctional structures in many animals and the presence of embryonic structures that have no counterpart in the adult Lamarck believed that the Earth was very old Charles Darwin 18091882 Charles Robert Darwin was born in Shrewsbury England in 1809 The son of an eminent local doctor Dr Robert Darwin Charles was born into a modestly wealthy family He was the grandson of Erasmus Darwin English naturalist and promoter of the idea of evolution Darwin studied medicine at Edinburgh University from 1825 to 1827 He transferred to Christ s College Cambridge in 1828 with the intention of becoming a minister in the Church of England He was a mediocre student and did not like classical education His interests were in natural history botany geology collecting and hunting In 1831 with the help of his botany professor John Henslow and his uncle Josiah Wedgewood he took the post of naturalist on board the HMS Beagle on a scienti c mission to South America By the time of his return in 1836 he had become an authority on many forms of life Between 1842 and 1844 he developed his theory ofnatural selection although he did not announce his work until 1858 In 1859 he published a considerably eXpanded version of his researches in the controversial Origin ofSpeeies by Means ofNatnral Selection He published The Descent oann in 1871 THE VOYAGE OF THE BEAGLE HMS Beagle under the command of Captain Robert Fitzroy left for Patagonia South America in 1831 with Charles Darwin on board At this time Charles did not believe in evolution including his grandfather s theory as any evidence presented so far could not convince him The Beagle reached South America in 1832 and Charles took care to observe the ora and fauna Charles went then to Buenos Aries where he saw fossils of more ancient animals including a mastodon He experienced a violent earthquake in Chile that raised the land in some places between 2 and 10 feet Darwin was most interested in the plants and animals on the Galapagos a group of 16 large islands and many smaller off the coast of Ecuador Giant tortoises inhabit every one of the islands which gave the island chain its name from the Spanish Galapagos meaning tortoise Each island has its own type of tortoise distinguishable by the shape and pattern of its shell Darwin was astonished that the islanders felt that this was due to the difference in environment on each island Darwin also observed the nches which varied in size and shape from island to is an Their beaks also varied depending on which food they ate and some even had eXtra long tongues for grabbing certain types of foods such as insects nuts or seeds Island animals and plants were different to those on the mainland but a relationship could be seen What was even stranger though to Darwin was the fact that organisms on different islands varied but still seemed related ALFRED RUSSEL WALLACE 18231913 8 January 1823 Alfred Russel Wallace born at Usk Monmouthshire midlate 1837 Joins the eldest brother William in Bedfordshire to learn the surveying trade 25 April 1848 Wallace and Bates leave England for Amazonian South America to begin a natural history collecting eXpedition March 1854 Leaves England for the Far East to begin a natural history collecting eXpedition 20 April 1854 to 20 February 1862 Collecting eXpedition in the Malay Archipelago February 1858 Writes 39On the Tendency of Varieties to Depart Indefinitely From the Original T ype39 and sends it off to Charles Darwin for comment 1 July 1858 Wallace and Darwin s writings on natural selection are presented at a meeting of the Linnaean Society November 1859 On the Zoological Geography of the Malay Archipelago the paper describing Wallace s Line is read before the Linnaean Society Darwin s On the Origin of Species is published 1 April 1862 Returns to English soil o 7 November 1913 Dies at Old Orchard quotIn February of 1858 while suffering from an attack of malaria in the Moluccas it is not fully certain which island he was actually on though either Gilolo or Ternate seems the likely candidate Wallace suddenly and rather unexpectedly connected the ideas of Thomas Malthus on the limits to population growth to a mechanism that might insure longterm organic change This was the concept of the quotsurvival of the ttest in which those individual organisms that are best adapted to their local surroundings are seen to have a better chance of surviving and thus of differentially passing along their traits to progeny Excited over his discovery Wallace penned an essay on the subject as soon as he was well enough to do so and sent it off to Darwin He had begun a correspondence with Darwin two years earlier and knew that he was generally interested in quotthe species questionquot perhaps Darwin would be kind enough to bring the work titled 39On the Tendency of Varieties to Depart Inde niter from the Original Type to the attention of Lyell httpwwvv wkn 4 39 39 39 39 39 l htm DARWIN S EVOLUTINARY THEORY Darwin s evolutionary theory has two thesis 1 Descent with modi cation All living and extinct species have descend without interruption from one or several original forms of life These new species accumulated changes over great expanse of time and now look different from one another 2 Natural Selection Useful variation will allow those organisms that possess them to survive and reproduce and pass these good variations to their offspring DARWIN S THEORY OF NATURAL SELECTION Fact 1 Without 39 l l 39 39 will grow 1 39 quot producing an ever more rapidly growing number of organisms Fact 2 In spite of this prediction the numbers of individuals in a population remains near equilibrium uctuating above and below some mean value Fact 3 Resources are limited From these three facts Darwin concluded that there was a struggle for existence Darwin combined this with two additional facts Fact 4 Individuals are unique There is individual variation This came from observing animal breeding Fact 5 Much but not all of the individual variation is heritable This observation also came from animal breeders Some of the observed variation is environmental some is genetic Conclusion These facts led Darwin to the conclusion that some individuals are better equipped to survive and reproduce Natural Selection in their struggle for existence Through many generations of time evolution is the result Darwin used quotdescent with modi cationquot Mayer 1982 stated that Darwin s Theory of Evolution included ve theories 1 Evolution as such lineages of organisms change over time 2 Common descent all life can be represented as a single family tree where there is common ancestor to all species 3 Gradualism gradual changes produced new species this is in contrast with saltation the hypothesis that proposes that evolution occurs by sudden leaps 4 Population change evolution occurs due to the proportion of individuals in the population that inherit a given characteristic 5 Natural selection survival and reproduction A big gap in Darwin s theory was the lack of an eXplanation about the origin of the variations found in a population where do these variations come from o Darwin s theory was a variational theory in which populations change due to survival reproduction and selection of certain genes 0 Lamarck s theory was a transformational theory in which the individual changes is transformed and then passes those traits to the offspring Blending Inheritance This was the prevailing hypothesis about the inheritance of traits o Maternal and paternal contributions blend in the offspring 0 As a result a new adaptation will be diluted in successive generations and eventually disappear Therefore variation should decrease and not increase Darwin never knew that Gregor Mendel had solved the problem of inheritance in a paper published in 1865 EVOLUTIONARY THEORIES AFTER DARWIN After Darwin s theory was proposed in the 1850s there was period of substantial controversy and several theories were proposed which included neolamarckism orthogenetic and mutationists theories A great deal of information was accumulated after the 1870 due to the work done in paleontology comparative morphology and comparative embryology o Neo Lamarckism several theories based on the idea of the inheritance of acquired characteristics Orthogenetic theory evolution proceeds toward a predetermined goal and does not require natural selection No mechanism was ever proposed for this theory o Mutationist theory geneticists observed that mutations arise and produce new variations in the population therefore natural selection was not necessary for evolution to occur the mutants represent new species THE EVOLUTIONARY SYNTHESIS This synthesis incorporates the information obtained by geneticists systematists and paleontologists into the theory of evolution proposed by Darwin Mutations are the raw material of natural selection Mutations recombination natural selection and other processes operating within species account for the origin of new species and for the major longterm features of evolution macroevolution Fundamental Principles of Evolution 1 Equot W 5 U 9 gt1 00 O N The phenotype is different form the genotype phenotypic differences may be due to genetics or environmental factors Environmental effects do not affect genes passed on to the neXt generation acquired characteristics are not inherited Genes retain their identity and do not blend Genes mutate usually at a slow rate Evolutionary change occurs in the population The rate of mutation is too slow for mutation alone to cause evolutionary change the shift from one genotype to another Natural selection can under certain circumstances bring about substantial evolutionary change in a realistic amount of time Natural selection can change the frequency of alleles that may recombine with other genes that affect the same trait and give rise to new phenotypes Natural populations are variable and can change rapidly when environmental conditions change Populations in different geographic regions differ in characteristics that have a genetic basis The number of different genes forms the basis for differences between populations of the same species and between species This supports the hypothesis that species evolved in a series of small steps Differences between geographic populations of a species are often adaptive and are the consequence of natural selection 13 Phenotype alone does not de ne a species there are different phenotypes within an interbreeding population Different species represent different gene pools and do not exchange genes with other species 4 Speciation is the origin of two or more species from a common single ancestor Speciation occurs by the genetic differentiation of a geographically segregated population U There are many gradations of phenotypic differences in living organisms assigned to species grouped under the same genus genera to families etc Higher taxa arise by the sequential accumulation of small differences rather by the sudden appearance of a new type 6 The fossil record has many gaps among quite different kinds of organisms but it also includes examples of gradation from ancestral forms to newer one EVOLUTIONARY BIOLOGY SINCE THE SYNTHESIS Since the 1950s advances in genetics and molecular biology have revolutionized the study of evolution In the siXties evolutionary theory has eXpanded into ecology animal behavior and reproductive biology Molecular evolution analysis of the processes and history of change in genes 0 Neutral History of Molecular Evolution a hypothesis that holds that the evolution of DNA sequences occurs by genetic drift rather than by natural selection Evolutionary Developmental Biology studies how developmental processes both evolved and constraints evolution Evo Devo for short 0 Tries to understand and determine the ancestral relationships of organisms and the processes involved in development Evolutionary Genomics deals with the variation and evolution of multiple genes and entire genomes PHILOSOPHICAL IMPLICATIONS The theory of evolution changed the essentialism of Plato and Aristotle and placed variation in its place 0 Every characteristic of a species can vary and radically so if given enough time The theory of evolution changed the static concept of the world for one of change Change and not stasis is the natural order Random purposeless variation acted on by blind purposeless natural selection provided a revolutionary new kind of answer to almost all questions that begin with Why The structures of organisms have a function not a purpose ETHICS RELIGION AND EVOLUTION Creationist movement literal reading of the creation stories found in the Bible The supposition that natural is good is called by philosophers the Naturalistic Fallacy There are no ethical or moral principles in science Science does not deny or affirm the eXistence of a Creator EVOLUTION A hypothesis is an educated guess an informed conjecture of what may be true A scienti c theory is a mature coherent body of interconnected statements based on reasoning and evidence that eXplain a variety of observations Evolution is a fact that is explained by the evolutionary theory Descent with modi cations is supported by evidence provided by paleontology geographic distributions of species comparative anatomy embryology genetics biochemistry and molecular biology How modi cations occur and how ancestors give rise to diverse descendants constitutes the theory of evolution A body of ideas about the causes of evolution including mutation recombination gene ow isolation random genetic drift the many forms of natural selection and other factors constitute our current theory of evolution Like all theories in science it is incomplete Carboniferous Period First synapsids like pelycosaurs evolve from stem reptiles Possess a skull fenestration in the temple providing for better jaw muscle attachment but otherwise possess few striking similarities with mammals Many members prove to be evolutionary dead ends Dimetrodon is a famous example Early Permian A synapsid line evolves into therapsids which become dominant at this point Beginning ofjaw modification and indication of a relatively lighter and more active body Also know as mammallike reptiles this term should be avoided Middle Permian Majortherapsid diversification as well as large body size Late Permian The therapsids known as cynodonts evolve They possess secondary palates greatly enlarged dentary and larger temporal openings implying complicated musculature Early Triassic Dinosaurs evolve Late Triassic Therapsid trend towards small size due to some unknown selective pressure They remain diminutive until after the Cretaceous The transition from reptile to mammal has an excellent record The following fossils are just a sampling In particular these fossils document the transition of one type ofjaw joint into another Reptiles have one bone in the middle ear and several bones in the lowerjaw Mammals have three bones in the middle ear and only one bone in the lowerjaw These species show transitional jawear arrangements Hunt 1997 White 2002b The sequence shows transitional stages in other features too such as skull vertebrae ribs and toes a Sphenacodon late Pennsylvanian to early Permian about 270 million years ago Mya Lowerjaw is made of multiple bones the jaw hinge is fully reptilian No eardrum b Biarmosuchia late Permian One of the earliest therapsids Jaw hinge is more mammalian Upperjaw is fixed Hind limbs are more upright c Procynosuchus latest Permian A primitive cynodont a group of mammallike therapsids Most of the lowerjaw bones are grouped in a small complex near the jaw hinge Thrinaxodon early Triassic A more advanced cynodont An eardrum has developed in the lowerjaw allowing it to hear airborne sound lts quadrate and articularjaw bones could vibrate freely allowing them to function for sound transmission while still functioning as jaw bones All four legs are fully upright 9 e Probainognathus midTriassic about 235 Mya It has two jaw joints mammalian and reptilian White 2002a f Dian hrognathus early Jurassic 209 Mya An advanced cynodont It still has a double jaw joint but the reptilian joint functions almost entirely for hearing g Morganucodon early Jurassic about 220 Mya It still has a remnant of the reptilian jaw joint Kermack et al 1981 Hadrocodium early Jurassic lts middle ear bones have moved from the jaw to the cranium Luo et al 2001 White 2002b 3quot Therapsids eg Dimetrodon the numerous therapsids fossils show gradual transitions from reptilian features to mammalian features For example the hard palate forms the teeth differentiate the occipital condyle on the base of the skull doubles the ribs become restricted to the chest instead of extending down the whole body the legs become quotpulled inquot instead of sprawled out the ileum major bone of the hip expands forward Cynodont theriodonts eg Cynognathus very mammallike reptiles Or is that reptilelike mammals Highly differentiated teeth a classic mammalian feature with accessory cusps on cheek teeth strongly differentiated vertebral column with distinct types of vertebrae for the neck chest abdomen pelvis and tail very mammalian mammalian scapula mammalian limbs mammalian digits eg reduction of number of bones in the first digit But still has unmistakably reptilian jaw joint Morganucodonts eg Morganucodon early mammals Double jaw joint but now the mammalian joint is dominant the reptilian joint bones are beginning to move inward in modern mammals these are the bones of the middle ear Hominid Evolution Distinguishing features and characteristics This chart of the Hominid family will categorize the known hominids by genus and species and if applicable the subspecies or other categorization Beginning with the oldest known species and moving forward chronologically it will give their age by oldest and youngest confirmed or conjectured date as notedthe creatures known locations and environments its distinguishing physical characteristics any technology it may or is known to have possessed and any social behaviors that are known or can be ascribed Conjecture about the species and their relationships to others will be included Finally some notable archeological sites or finds will be given Each paragraph of facts will be provided with source citations Due to size limitations this survey is presented in two parts Part 1 Early Primates In the Late Cretaceous 7O mya two varieties of primates existed the Strepsherinni a nocturnal bestiary and the Haplorini a diurnal variety from which hominids arose 1 Hominoid Superfamily This group contains species that would later develop into the hominid line and the great apes 1 Aegyptopithecus Found in the later Oligocene 2829 mya in Egypt and having a somewhat developed forehead small incisors lower premolars and large molars 1 Proconsul Three species major africanus and nyanzae all show hominid characteristics 1 Kenyapithecus wickeri A possible forerunner of the Pongid and Hominid lines 1 HOMINIDS Climatic cooling during Late Miocene 60 to 53 mya probably triggered speciation of Hominoid superfamily into the Hominid family along with other mammalian speciation 2 A Gap in Hominoid fossil record from 14 mya to 42 mya leaves these questions unanswered for the time being 3 1 Ardipithecus ramidus 44 mya 4 Hominoidhominid teeth A piece of the foramen magnum indicated upright posture 4 Leg and pelvis indicate a semibipedal mode of locomotion warranting a separate genus 5 ln Ethiopia the remains of 17 individuals have been found mostly teeth but a partial juvenile jaw partial cranium case and arm bone fragments from two individuals are included The environment at the time was temperate ortropical forest Discovered by Tim White in 1994 4 6 Australopithecines General The Lake Baringo jawbone could make this genus 5 million years old 3 Humanlike jaws and teeth apelike small skull 3 Gracile Bipedal but still tree climbers Pronounced cheekbones projecting jaws large teeth heavily enameled molars that indicate a primarily vegetarian diet A high degree of sexual dimorphism 9 Their remains have been found only on the African continent 3 1 Australopithecus anamensis 42 to 35mya 10 A thick tibia with a concave knob on top indicates bipedalism Parallel rows of back teeth are similar to apes likewise its small earholes 5 Found only in East Africa so far possibly forest dwelling 5 A lower left humerus 4 mya lower jaw with all teeth 415 mya and the upper and lower segments of a tibia 4 mya were discovered by Meave Leaky in 1995 around Lake Turkanna Nairobi Kenya 10 1 2 Australopithecus afarensis 39 mya to 3 mya 3 400cc braincase 9 Arms longerthan humans but shorterthan modern apes About four feet tall 3 Venous brain cooling mechanism modified from nonerect hominoids 7 Could have lived in African forests or savanna or both with tree climbing abilities 12 7 Some found in groups 6 A knee joint 34 mya the Lucy skeleton and the First Family of thirteen individuals 32 mya were discovered in the Afar valley Ethiopia by Donald Johansen in 1973 74 and 75 respectively Footprints 37 mya preserved in volcanic ash at Laetoli Kenya and discovered by Mary Leaky in 1976 may belong to this species In 1991 a 70 complete skeleton was discovered by Bill Kimbel and Yoel Rak and confirmed the skeletons and skull s belonged to the same species and confirmed the dimorphism of the species 6 Associated with an apelike grasping big toe found on two fully articulated feet and ankle fossils dated 35mya The pieces were discovered by Ronald Clarke in a university museum drawer in Johannesburg having been dug up from a mine shaft in the 70 s and mislabeled as chimpanzee s 12 3 Australopithecus africanus 23 mya Gracile variety 3 Modified venous brain cooling 7 440 to 485cc braincase capacity 6 Taung Childquot identified by Raymond Dart in 1925 and rejected by other anthropologists as a human predecessor is about 1 to 2 mya most scientists expected a largebrained ancestor with an ape like jaw and seemed to want to reject in any event an African genesis of human evolution The foramen magnum at the base of the skull indicated bipedalism At Mankapan South Africa Dart discovered the most complete Australopithecus to that date 1958 He named it Plesianthropus It was an africanus specimen and dated 23 mya 8 6 httpanthro7anthrouiuceduanth102sts5htm 3 mya 3 to 1 mya Paranth ropus General Formerly classified as a robust form of Australopithecus 3 Massive teeth and jaw muscles indicate vegetarian diet of coarse plant material 2 Recent examinations of its hand bones reveal that it could have manipulated stone tools quite well 31 African continent tropical forest dwelling 2 7 Stone tools have turned up in Ethiopia that have been dated to 25 to 26 mya the oldest ones discovered so far This makes the arrival and departure of the Oldowan tool industry coincident with the tenure of the Paranthropus species and from this some now suggest that it was Paranthropus and not early Homo that were the first tool makers 31 Enlarged sinus brain cooling mechanism derivative from Autralopithecines 7 4 Paranthropus aethiopicus 33 to 26 mya 33 quot 39 a quot the lquot genus 31 The Black Skull of Tanzania was discovered by Alan Walker in 1985 and is now considered by some a member of this species 33 5 Paranthropus boisei 26 mya 3 to 12 mya 2 Largest variety Sometimes with bony crests atop their skulls supporting massive jaw muscles Smallest hominid braincase recorded 410cc More prominent ridges more jutting face 3 A complete intact cranium missing only teeth with a braincase of about 510cc and dated 17 mya discovered by Richard Leaky in 1969 near Lake Turkana A smaller version without the bony crest dated to 17 mya and with a 500cc braincase was discovered by the same Leaky in the same area in 1970 6 6 Paranthropus robustus 26 mya to 18 mya 3 31 Zinjanthropus or Nutcracker Manquot an almost complete cranium with a 530cc capacity was discovered by Mary Leaky in 1959 at Olduvai Gorge in Tanzania dated to 18 mya 8 6 Once classified as A boisei 3 HOMO Early Homo 23 mya 32 Though early varieties were very similar in form and physiology to Australopithecus the key difference is a much larger and complex brain allowing a significant toolmaking ability 2 This Homochauvinism with regard for the capacity to make tools is now under question 31 Homo is characterized by a more generalized skull construction less prominent ridges and less protruding face Early Homo had diminished premolars and emergence of third molar wisdom tooth and were omnivorous Sexual dimorphism is far less pronounced 2 Probably pair bonded and were scavengers 2 The earliest known Homo fossil specimen has been dated to 23 mya and shows characteristics not unique to either habilis or rudolphensis The fossils two halves of an upper jaw were found associated with Oldowan style tools From otherfossils found in association its environment is deduced to be a drier more open one where the forests of its ancestors age has retreated 32 1 H rudolfensis Est 25mya to 18mya 2 Conjectured from a small quantity of fossils and tools has affinities with habilis and maybe ergaster and erectus 2 Tool use is now under question and may be removed from this creature s resume and assigned to the Paranthropus genus for this time period 31 Associated with simple Omo tool technology 2 Associated with catchment scavenging congregating near locations that offers many different needed resources such as lake margins stream confluence and rock outcroppings 2 A very complete skull found by Bernard Ngeneo in 1972 dated 19 mya and with a braincase of 750 cc has been tentatively assigned to this species lts leg bones were found nearby 6 The Dik Dik Hominidquot discovered by Tim White in 1986 dated 18 mya comes with skull arm leg and teeth all closely resembling habilis but also similarto afarensis 6 2 H habilis 16 mya to 2 mya 14 Concurrent with A africanus for a time Larger brain than Australopithecus 800cc omnivorous teeth and a third molar like moderns Rounder head smaller face narrower teeth less pronounced brow ridges slight chin almost hairless face 14 Skull Casts show an enlargement of the Brocca s area of the brain which is responsible for speech in Homo sapiens 33 With long arms short legs and Australopithlike thigh anatomy 2 Stood 37 to 42 feet tall May have had the ability to make simple single face stone tools Omo used mainly for cutting and chopping vegetables and plants and scavenging meat 14 This tool making ability is now being questioned 31 Probably not a hunter but lived by catchment scavenging 2 Morphologically too primitive to be an ancestor of ergaster or erectus 2 The exact attributes of habilis are disputed some believing that much that has been assigned to it actually are fragments that belong to H rudolfensis 31 Many fragments jaws teeth cranial hand and foot bones etc were discovered by the Leakys in the early 1960 s and giving a braincase measurement of 660 to 680 cc 6 Twiggy a complete if crushed cranium and seven teeth with a braincase of 590 cc dated 185 mya was discovered by Peter Nzube in 1968 6 At the Omo Valley Kenya Australopithecus remains have been discovered contemporaneously with H habilis 8 A stone circle the first architectural structure dated 18 mya could be habilis or erectus 1 3 H ergaster 2 mya 15 Much larger brain than habilis 1000cc More generalized skull features than erectus rounder head higher cranial dome less protruding lighterfacial features very slight eye ridges Morphologically closer to H sapiens than erectus 15 Its fossils were once classified as erectus 3 Starting in African tropical and sub tropical zones Territory scavenging exploiting many locales with one or two resources each across a wide area and associated with Acheulean technology typifies ergaster s living habits This allowed ergaster to survive the wide sparse landscape of the plains and temperate drier climates 2 Some ancestor to ergaster and erectus arose in Africa during the cooling of the Middle Pliocene approximately 25 to 20 mya Some migrated to Eurasian continent taking Oldowan tools with them 2 Began with simple Omo tools progressed to Acheulean technology complex bifacial tools with more careful selection of cores and more complicated chipping patterns that made use of the entire edge of the tool Early examples by 2 mya a complete set of Acheulean tools by 15 mya 2 Good probability that ergaster was an active hunter as opposed to a scavenger 2 The famous Turkana Boyquot discovered by Richard Leak39s Hominid Gang in 1984 a very nearly complete skeleton of a juvenile who probably drowned 16 mya is now classified as ergaster 4 H erectus 800000 to 400000 ya Larger brain and body than habilis Sister species to H ergaster very similar in physiology and form but not as smart Brain case of about 1000 cc fully upright and bipedal Differences include a longer skull low forehead thick cranial bones large projecting brow ridges and a heavier face than sapiens 2 As tall as modern humans 3 Found in tropical Africa but mainly in Asia Indonesia and points in between 2 Cooling due to glaciation during Middle Miocene probably prompted to migration of erectus or her immediate ancestor to Eurasian continent possibly related to migration of six bovid species following forest recession through Saudi Arabia tropical and subtropical zones and into south central China and across land bridge to Java Later moved into temperate zones in Western Asia at end of ice age approximately 14 mya 2 Asian erectus is associated with Omo and early Oldowan stone technologies but nothing near as complex as Acheulean or developed Oldowan 2 Lived by catchment scavenging which may have helped spread species across Eurasia 2 ln Chokoutien Cave Dragon Bone Cavequot China erectus remains have been found dated to 500 tya including bone remains evidence of fire omo type tools 8 In the River Solo Java Eugene Dubois discovered the remains of the first quotJava Manquot in 1891 8 5 H antecessor 10 mya 2 to 800 tya 16 Relatively modern sapienslike face less protuberant than ergaster or heidelbergensis Other cranium features lower jaw and teeth are more similar to ergaster than to sapiens or heidelbergensis Braincase capacity 1000cc 16 Lived in Europe and Northern Africa when climate was similar to today s in oak pine and beech forest 16 Associated with coreflake tools Omo variety 2 Probably the last or closest common ancestor to sapiens and heidelbergensis 16 Perhaps arose in Africa and migrated to Europe spawning heidelbergensis while relatives left behind gave rise to sapiens in Africa 2 At La Sima de los Huesos near Atapuerca in Northern Spain the species was identified by the remains of at least six individuals dated 800 tya found deep in a cave that may once have had another entrance The bodies may have been deposited there in ritual burial 16 Elementary coreflake technology found at lsernia La Pineta Italy and dated to 800tya could be assigned to antecessor 2 Some tools and hominid fragments including skull and limb pieces have been dated to 1 mya at Orce south central Spain in 1996 2 6 H heidelbergensis 600000 to 250000 ya Tall as ortaller than modern humans Precursors to Neanderthals with robust physiques big noses no chins heavy brows and various braincase sizes 17 Some kinds of bifacial stone tools Acheulean 2 Wear on teeth shows use of bite as third handquot while using tools 18 Capable of group hunting large game 18 Scrape marks on bones indicating defleshing may be sign of cannibalism Hints of knowledge of mortality bodies dumped at Atapuerca in ritual 17 Probable ancestorto H neanderthalensis but not H sapiens 17 Heidelberg Germany site of cave where Mauer Jawquot was found in 1908 it was originally attributed to erectus and later true Neandertals 8 ln Petralona Greece in 1960 villagers discovered remains that have been estimated to be from 250 to 500 tya Once classified with archaic Homo it has erectusergaster and Neandertal characteristics 6 7 H neanderthalensis 230000 to 29000 ya Larger bodies more stocky and barrel chested than sapiens and heidelbergensis 18 Distinct inner ear bones farther from sapiens than even apes 19 Their brains were on average larger than modern humans 18 though brain case impressions show a lack of frontal lobes 20 Also characterized by the occipital bun at the base of the brain in classic Neandertals 18 Ranging from Europe to the Middle East in ice age and later in their existence temperate climates also found in Asia and Northern Africa 18 Like H heidelbergensis they used their front teeth to hold objects while working with tools 18 They employed Mousterian technology a style of stone tool industry characterized by flakes chipped into points triangles burins chisels borers for soft materials and drills for hard items 13 They had no fine points or blades This technology would remain largely unchanged over most of theirtenure on Earth 3 Known to have used wooden spears but not for throwing only stabbing and thrusting 18 Chatelperonian style stone tools came about coincident with the arrival of modern sapiens to Neandertal s territories 40 tya and were the result of their borrowing from the Aurignacean toolkit The presence ofjewelry made of antler and bone indicates attempts by moderns to trade with Neandertals 19 A flute has been discovered associated with Neandertal remains dating 43tya to 67 tya lt matches the seven note diatonic scale of modern human music 34 They were social huntergatherer people living in bands of twenty to forty practicing cooperative hunting and caring for their sick and wounded Many individual specimens show signs of massive and multiple injuries to the upper body They probably also had a language capability Scrape marks on some skeletal remains made by stone tools could be signs of cannibalism or ceremony for the dead A Neandertal grave in Shandar lraq contained the remains of four individuals a man two women and an infant and the pollen of spring flowers 18 Other graves have been discovered with animal horns flowers and red ochre 3 The only known art object attributable to neandertals is a single carved and polished baby mammoth tooth veined with red ochre found in Hungary and dated 80 to 100 tya 18 In the Neander Valley Germany a limestone cave containing remains and some tools discovered in 1856 gave the species its name In that year Professor D Schaaffhausen of Bonn studied them and declared that they were from a wild northern tribequot older than the Celts This conclusion was totally rejected by the leading naturalists of the day The remains significance would not be recognized for about fifty years 3 ln Krapin Yugoslavia about eighty individuals were discovered around the turn of the century confirming their uniqueness and nonsapiens morphology Some had intentionally scraped and broken large bones indicating possible cannibalism The remains are dated 130 tya 18 8 At Shandar Iraq is a neandertal living and burial site the graves containing pollen grains and the remains of very old and healed wounded people 100 tya A second occupation of the cave occurred around 50 tya 18 8 H sapiens Early Moderns 200000 ya to 50000 2 The first sapiens was not anatomically similarto modern sapiens 22 Largest braincase 1200 cc to 1400cc relative to body size otherthan moderns 3 18 Capable of language symbolism other abstract concepts Slighter body built than neanderthalensis 18 Evolved in Africa 2 They evidenced fine detailed toolmaking at their emergence judging from barbed bone harpoons discovered in Zaire dated to 200 tya but widespread tool use was limited to the more primitive mousterian style until the advent of Aurignacian technology around 40 tya 2 9 H sapiens CroMagnon 50000 ya to present 2 Anatomically similarto modern humans Beginning in Sub Saharan Africa and a temperate climate they would eventually adapt to all extremes of heat and cold 23 They ranged from Northern Africa to Southern Asia and across Europe They took advantage of the lowered sea levels and connections via land to migrate across the Bering Land Bridge beginning around 20 to 10 tya 22 Others suggest that they might have crossed via a GreenlandNova Scotia route over ice land and with small sea vessels across short distances The first North American immigrants were Caucasoid and were later replaced by Asian tribes who were the ancestors of modern Native Americans 24 CroMagnon s tools are described as the Aurignatian technology characterized by bone and antler tools such as spear tips the first and harpoons They also used animal traps and bow and arrow 22 They invented hafts and handles for their knives securing their blades with bitumen a kind of tar as long ago as 40 tya 25 Other improvements included the invention of the atlatl a large bone or piece of wood with a hooked grove used for adding distance and speed to spears They also invented more sophisticated spear points such as those that detach after striking and cause greater damage to prey 26 They also began the marking of time with the lunar phases recording them with marks on a piece of bone antler or stone Some of these calendars contained a record of as many as 24 lunations 27 In the relatively recent past tool industries diversified The Gravettian industry 25 to 15 tya characterized by ivory tools such as backed blades is associated with mammoth hunters One type of brief industry was Solutrean occurring from 18 to 15 tya and limited to Southwest France and Spain It is characterized by unique and finely crafted laurel leafquot blades made with a pressure technique requiring a great skill The industry is associated with horse hunters The Magdalenian Culture 15 to 10 tya produced the widest variety of tools bone needles harpoons microliths small blades 13 cm This was a culture of reindeer hunting When the glaciers receded the culture and the industry dissipated 13 The tool industry of the Clovis Culture in North America 11 to 8 tya is notable for its remarkable similarity to Solutrean Some suggest that the Solutrean culture migrated to North America around 10 to 15 tya 24 Cro Magnon people lived in tents and other manmade shelters in groups of several families They were nomadic hunter gatherers had elaborate rituals for hunting birth and death 22 Multiple burials become more common From 35 to 10 tya there was no statistical trend in differentiation by sex or age in burials They included special grave goods as opposed to everyday utilitarian objects suggesting a very increased ritualization of death and burial Symbolic representation by personal adornment in burial becomes more common 28 They were the first confirmed to have domesticated animals starting by about 15 tya 22 though ancient sapiens may have domesticated the dog as much as 200 tya 29 They were the first to leave extensive works of art such as cave paintings and carved figures of animals and pregnant women Huge caves lavishly decorated with murals depicting animals of the time were at first rejected as fake for being too sophisticated Then they were dismissed as being primitive categorized as hunting fertility or other types of sympathetic magic Reevaluations have put these great works of art in a more prominent place in art history They show evidence of motifs of following their own stylistic tradition of impressionist like style perspective and innovative use of the natural relief in the caves Also possible considering the new concepts of time reckoning practiced by Cro Magnon are abstract representations of the passage of time such as spring plants in bloom or pregnant bison that might represent summer 30 Aside from pregnant women and other goddess worship iconography 35 representations of people anthropomorphs are very few and never show the accuracy or detail of the other animals Humans are represented in simple outlines without features sometimes with masks often without regard to proportion distorted and isolated 30 At Grottes des Enfants France are found four burials with red ocher and associated with Aurignacian tools 8 At Lascaux France are the famous caves of upper Paleolithic cave art dated to 17 tya Due to moisture damage they have been closed to tourists since 1963 but since 1984 people have been able to walk through a manmade recreation that took five painstaking years to make situated about two hundred yards from the actual site 3 Kennewick Man found in 1996 on the banks of the Columbia River in Washington US dated to 9600 years ago is at the center of a furious political debate between anthropologists who want to study the nearly complete skeleton and the leaders of a coalition of five Columbia River basin American Indian tribes who claim the remains as theirs by law though it is older than the tribes and who want to reinter it It is now in the possession of the US Army Corps of Engineers awaiting the decision ofthe US District Court and could go to the US Supreme Court 24 HOMINID EVOLUTION AUSTRALOPITHECUS Moving into Pliocene and Pleistocene epochs First definite hominids Grouping called Australopithecus Fossils from Tanzania 4000000 BP Fragmentary mandibles from Kenya suggest up to 4000000 BP Definite upright hominid Bipedal Teeth pelvis indicate upright By 2300000 BP tool user Increase in brain size 380775 cc Climate of the earth had been cooling during the Cenozoic Cooling reaches a maximum during Pleistocene Environment of East Africa cool and moist expansion of grasslands Remains are quite abundant 600 individuals found Concentrated in South and East Africa Possibly occurred entire tropical areas of the Old World Lots of interpretations Possibly dealing with more than one species of fossil hominid Australopithecus Fossil Evidence Remains of Australopithecus first discovered in 1924 Taung South Africa Mining limestone by blasting fossils uncovered Raymond Dart receives box of fossils Fossil baboons Reconstructs One rock shows a brain cast larger than a baboon Reconstructs face and brain Teeth like that of a 6 yr old child Humanlike not apelike Braincase mold not apelike 440 cc size of fullgrown male chimp Lowerjaw reconstructed hominid dental palate U Reduced canines Dart called creature Australopithecus africanus southern ape Said it was much closer to hominid than pongid and probably walked upright Spinal cord opening underneath Ideas were rejected 1930 s more discoveries in South Africa lndicate similar but larger creatures Limestone caves Sterkfontein pelvis More larger varieties Indicates we are dealing with two species of Australopithecus Australopithecus africanus smaller more general 60 lbs 4 ft 8 in Australopithecus robustus rugged 120 lbs more specialized apelike Evidence that Australopithecus africanus was violent Taung cave baboon skulls smashed Crude stone tools Oldowan Brain structure Australopithecus africanus Taung 440 cc 6 yr old Estimated ages from South Africa Limestone hard to date 1175 miion BP Relative dates Larger more apelike forms found in younger stratigraphy East Africa Material Ethiopia Afar Triangle Parts of 3564 individuals 29000003100000 BP Australopithecus afarensis Lucy complete skeleton Laetoli Tanzania Mary Leaky KA dates close to 4000000 BP Jaw fragments from Kenya close to 5560 million BP Olduvai Gorge Kenya Former lake bed Long hominid sequence Australopithecus Homo erectus Small form of Australopithecus in lower levels robust form of Australopithecus in higher levels Louis B and Mary Leakey long period of working Identify third form Homo habilis Claim direct line to Homo sapiens Size similar to Australopithecus africanus East Rudolf Kenya Richard Leakey 1974 KNMER1470 surprisingly modern looking skull at early date 775 cc large New KA date 19 million BP More advanced than either variety of Australopithecus Possible third form Cultural Evidence Paleolithic Old Stone Age Lower Paleolithic Cultural remains associated with Australopithecus africanus and Homo habilis Crude stone tools Oldowan sharpened pebbles Appears that Australopithecus africanus may have hunted Interpretations Australopithecus africanus gives rise to both Homo habilis and Australopithecus robustus Australopithecus robustus more primitive apelike becomes extinct Homo habilis gives rise to subsequent grades of hominids Two possibly three species overlapping in time and range For example the position of humans within the taxonomy is as follows Class Mammalia Subclass Theria lnfraclass Eutheria Order Primates Suborder Anthropoidea lnfraorder Catarrhini Superfamily Hominoidea Family Hominidae Genus Homo Species sapiens A more complete picture of where Homo sapiens stand in the grander scheme of things can be found below Some terms that may need defining are Catarrhini infraorder Old World Monkeys Platyrrhini infraorder New World Monkeys Pongidae family Chimpanzees gorillas and orangutans Hylobatidae family Gibbons Pan genus chimpanzees Pongo genus orangutans ARCHAEOLOGICAL SITES CHOUKOUTIEN CAVE also spelled Zhoukoudian Location Dragon Bone Hill China Date 400000 to 500000 years This site located 27 miles from Peking has provided us with numerous Homo erectus remains as well as many interesting artifacts The tools have been manufactured from quartz using a flake process Examination of the site has revealed that the people who used this site were part of a huntergatherer society They lived in an environment that was a mixture of deciduous and coniferous forest and that they used this area during a time when the weather was cool to seasonany cold and damp The finds at this location include the earliest known use of fire by hominids as evidenced by hearths and charred animal bones These same sites also show the earliest evidence of possible cannibalism FONTECHEVADE Location France Mademoiselld G HenriMartin uncovered five distinct levels at this site From the surface down these layers correspond to a Magdalenian occupational level an Aurignacian level a Mousterian living floor an undisturbed stalagmite layer a stratigraphic layer containing one skull cap fragments of a frontal lobe and remains of warm climate fauna corresponding to the last interglacial of the Ice Age GROTTES DES ENFANTS Location France In 1894 this site in France provided us with four burials whose inhabitants were stained with red ochre These burials were found in two layers with two graves in each Those graves in the lower layer contained individuals who were buried in the fetal position while those in the upper layer were fully extended The upper layer graves were also accompanied with tools of the Aurignacian industry and are attributed to the CroMagnon population Homo sapiens sapiens Hadar Ethiopia It was at this site that M Taieb and DC Johanson found the famous Australopithecus afarensis fossil Lucy Outside of this find this site in the Awash Valley has proven to be extremely rich in hominid fossils HEIDELBERG Location Germany The oldest Homo erectus fossil is found at this site with a date of 650000 years old JEBEL QAFZEH Location lsrael Date 100000 years This Homo sapiens sapiens cave site provided us with a look at twentyfour layers of identifiable remains many of which included living floors The tools at this site were of the Levallois Mousterian type and dates to approximately 100000 years ago This site shows that Neanderthals were not the only population that made and used Mousterian type tools Obviously this population had also picked up that skill Remains at this site include those of adults infants and one small child KENT39S CAVERN Location England This limestone cave was discovered by Reverend John MacEnery Inside was found the remains of stone tools as well as the bones of several species of animal Many of these animals were now extinct which proved that before the Flood hominids lived in England with these now extinct animals This of course did not sit very well with the Roman Catholic Church KRAPINA Location Yugoslavia Professor GorjanovicKramberger uncovered thousands of animals remains and hundreds of human fossils at this Neanderthal site located in present day Yugoslavia The human fossils found include the remains of at least ten individuals including the first examples of Neanderthal children Artifacts such as tools of the Mousterian tradition have also been found at this local Burnt and intentionally broken human bones were also left behind which have been interpreted as being evidence of some form of cannibalism Nine living levels were counted at this site LA CHAPELLEAUXSAINTS Location France This intentionally buried skeleton found by three French priests Abbes A Bouyssonie J Bouyssanie and L Bardon on August 3 1908 is representative of a male Homo sapiens neanderthalensis of rather old age It was uncovered in a limestone cave along with Mousterian type tools made of flint and fossil bones of numerous animals such as wooly rhinoceroses reindeer hyenas and bison These animals are indicative of a colder climate most probably that of the Wurm glaciation LAETOLI Location Tanzania The site of Laetoli is probably most famous for the discovery that Mary Leakey and her archaeological team made in 1978 Here they uncovered the remains of the footprints of two or three hominids that were made in volcanic ash The walk took place just after a rain which made the ash more likely to hold the shape of the stroller39s footprints The distance between the footprints indicates that the two individuals were walking and therefore is definite evidence of bipedalism among the early hominids LANTIAN Location China This site is the oldest known of any Homo erectus site dating back 800000 years LES EYZIES Location France In 1868 L Lartet uncovered remains of Homo sapiens sapiens in this limestone cliff dated to the Cretaceous era The remains consist primarily of four adult skeletons and one neonate Above these remains was unquestionable evidence of several successive living floors Since these remains were found below the actual living floor it is believed that these individuals were intentionally buried Along with the human remains were found tools of the Aurignacian industry seashells several of which had been pierced and animal bones of reindeer bison and mammoth MAKAPAN Location South Africa Raymond Dart found most of the skull and face of an Australopithecus africanus here in 1958 NEANDER VALLEY Location Germany This is the type site for Homo sapiens neanderthalensis It is a cave Feldhofer grotto carved into limestone of the Devonian period Any tools orfauna did not accompany fossil remains at this site and since limestone does not form in distinct stratigraphic layers this site has proven difficult to date However estimates put it at approximately the fourth glaciation the Wurm OLDUVAI GORGE Location Tanzania Olduvai Gorge is one ofthe most successful sites excavated by Mary and Louis Leakey In 1959 this husband and wife team found the remains of an individual they called Zinjanthropus and which was dated at 176 million years ago Lower sediment layers at this site support evidence of Homo habilis occupation while in higher layers remains of Homo erectus can be found It was the habilis remains that helped to confirm the theorythat the hominid lineage originally came from Africa Olduvai is significant in many ways Stone circles found in the habilis layers may be evidence of the first quotarchitecturalquot structures Olduvai was also very instrumental in helping anthropologists construct the evolutionary history of tool cultures This site supports the longest sequence of tool evidence from Oldowan to Developed Oldowan to Acheullean to Middle and Later Stone Age In 1962 site MNK ll revealed pieces of a young adult of Homo habilis ancestry This find was named by Professor Philip Tobias and Dr John Napier and was important because it was classified as a member of the Homo line not based solely on the size of the brain Important features that Tobias and Napier used to make their decision were the shape of the rear and vault of the skull and the teeth Before the Leakey39s this site was searched by Professor Hans Reck of Germany In 1913 Reck uncovered a human skeleton perhaps buried for it was found in the fetal position However when World War I broke out Reck was taken as a prisonerofwar and was held in an Egyptian camp run by the British Any further discoveries were left until after the war was over OMO VALLEY Location Ethiopia It was at this site that Homo habilis remains were found to be contemporary with Australopithecus finds PAVILAND CAVE Location Whales This limestone cave was home to what has become known as quotThe Red Lady of Pavilandquot The remains of this young man originally thought to be a woman were stained with red ochre perhaps indication of religious beliefs This young man was also found with stone bones and ivory tools as well as with many types of animal bones When this cave was originally found the remains inside of it were explained by the Big Flood The animal remains found within the cave were thought to have been swept into the cave by the floodwaters and the skeleton was thought to have been buried there after the waters retreated and quotmanquot settled in England RIVER SOLO Location Trinil Java Dr Eugene Dubois is known for the finds that he made at the River Solo on Java In 1890 Dubois uncovered the first hominid remain at this site which included a tooth and skullcap In 1891 the second discovery of a femur and a second tooth were found These two discoveries were found only a few yards away which lends support to the belief that they all belonged to a single individual and were moved to these locations by the flowing river The skull fragment lends itself to an interpretation of a cranial capacity of 850 cc twothirds that of modern hominids The two teeth are archaic in design however they do differ from those of the apes The braincase was more representative of apes than of hominids howeverthe areas believed to be associated with language production were visible These remains were originally classified as Pithecanthropus erectus Homo erectus SHANIDAR Location Iraq Shanidar cave is a Neanderthal site that was excavated by R Solecki during the years 1951 to 1960 Here Solecki and his team found the remains of nine separate individuals who were apparently buried with some sort of religious significance Pollen analysis has provided us with the knowledge that these individuals were buried with several kinds of colorful flowers To anthropologists this represents the first solid evidence of religious beliefs among earlier hominids Many of these plants also have some sort of medicinal properties and therefore may be further indication of an early former of medicine ST CESAIRE Location Pierrot39s Rock France Discovered by F Leveque in July 1979 this site is situated along a small stream at the base of a limestone cliff Skeletal remains were found with tools of the Chatelperronain industry Above the skeleton the tools were of the Aurignacian culture while below the fossils were tools of the Mousterian industry hearths and carbonized debris Analysis of the biologic and archaeological remains put this site somewhere within the last glaciation the Wurm Radiocarbon analysis date this site as being 34 to 31 thousand years old These dates are rather old to be Neanderthal but may reflect the very last appearance of Neanderthals in Europe STEINHEIM Location Germany It was in this gravel pit that several layers of remains providing a look in the evolution of modern hominids were found Directly below the surface was strata containing remains of a cold weather fauna Below this was a layer containing remains representative of a warmer climate most probably the second or third interglacial phase The skull of a young female showed the cranial capacity to be 1070 cc The skull itself was long and narrow and was missing the mandible and the left side of the face The large brow ridges and powerful jaw were those of a Neanderthal while the rounded back of the skull was that of a modern hominid The features were less specialized than those of the classic Neanderthals which Leakey believed was a quotproduct of overspecialization away from common stem which gave rise to Homo sapiensquot Leakey 1969 STERKFONTEIN Location South Africa Yet another cave site in South Africa excavated by Robert Broom in 1936 Uncovered was the brain case on one adult SWANSCOMBE Location Thames Valley England Date 225000 years In a layer of river sediment located two feet below the surface archaeologists uncovered several skull fragments tools ofthe Middle Acheulean culture handaxes flake tools and numerous remains of 26 species of animal These animals are of those species eg wolf lion horse that would have lived in this area during an interglacial stage The skull fragments consist of a left and a right parietal which one can piece together like the pieces of a jigsaw puzzle They are well preserved and tell us that the individual was a young adult most possibly a female with a cranial capacity of approximately 1325 cc The pieces represent a modernlooking individual with the exception that the bone fragments found are thicker than in modern hominids Besides this everything else eg the positioning of the foramen magnum are indications of the trend towards the modern appearance Some believe that this individual is representative of the transitional period from Homo habilis to Homo erectus a population that would eventually give rise to the Homo sapiens subspecies Homo sapiens neanderthalensis TAUNG Location South Africa In 1934 Professor Raymond Dart of Witwatersrand University uncovered the remains of a small Australopithecus africanus child The remains showed a combination of hominid and pongid characteristics and because of this there was much discussion over whether this individual should be classified as a manlike ape or an apelike man The combination of characteristics resembled what one would expect to find forthe transition between ape to hominid the long sought for quotmissing linkquot in some respect This find was especially important because it provided the muchneeded evidence to support Charles Darwin39s claim that the ancestors to modern Homo sapiens would be found in Africa Last revised October 17 1995 bsklaruiucedu ANTHROPOLOGY 233 HUMAN EVOLUTION McBREARTY SPRING 1996 AFRICAN PLIOCENE amp PLEISTOCENE HOMINIDS Ardipithecus ramidus Site East African Rift Valley Aramis Middle Awash region of Afar Ethiopia Dates c 44 40 Ma Fossils Teeth amp jaws occipital fragments humerus radius ulna Body size c 40 kg Brain size Apelike precise size not known Teeth Canines large posterior teeth relatively small no apelike honing facet on canines premolars not molarized thin enamel dental arcade shape similar to A afarensis but canines in line with posterior teeth like apes Skull Foramen magnum placed anteriorly Postcrania Forelimb a mixture of apelike and A afarensislike features no adaptation for knucklewalking Tools None Habitat Floodplain Forest or woodland vegetation Australopithecus anamensis Sites Allia Bay amp Kanapoi East Turkana Kenya Fossils Tibia humerus temporal teeth amp jaws Dates Allia Bay 39 Ma Kanapoi 34 31 Ma Body size 4560 Kg very dimorphic Brain size Apelike precise size not known Teeth Large canine no honing facet on canine thick enamel on all teeth Skull Mandibular articulation amp external auditory meatus size amp shape chimplike Postcrania Bipedal less flexibility in ankle amp big toe than chimp powerful climber Habitat riverine floodplain mixture of open savanna amp woodland fauna Australopithecus afarensis Sites East African Rift Valley Afar Hadar Ethiopia Laetoli Tanzania Fossils Many individuals cranial dental amp postcranial remains AL2881 quotLucyquot 40 complete female partial skeleton AL333 quotFirst familyquot AL4442 Nearly complete male cranium Dates Laetoli 35 Ma Hadar 3034 Ma Body size c 2560 kg Height c 3393quot to 5397quot Very dimorphic females c 65 of male body weight Brain size Small ape range 400500 cc Teeth Large dimorphic canines diastema sometimes present incisors fairly large molarized premolars molars large low crowned with thick enamel tooth rows converge at rear third molar smaller than first and second molars Skull Prognathic nuchal crest amp sagittal supraorbital torus in males foramen magnum placed anteriorly Postcrania Bipedal features Humanlike carrying angle of knee shallow broad pelvis big toe in line with other toes Other features indicate possible climbing ability Long forearms curved finger amp toe bones upward facing shoulder socket Tools None Habitat Woodland amp semiarid savanna Australopithecus africanus Sites South African caves Taung Sterkfontein Makapansgat Fossils Many individuals cranial dental and postcranial remains Taung Nearly complete juvenile cranium STS 5 Nearly complete adult cranium Sterkfontein quotMrs Plesquot Dates 2823 Ma Brain size Small ape range lt 450 cc Body size Similarto A afarensis Dimorphic c 25 40 kg Teeth Parabolic dental arcade large molars amp premolars with thick enamel small incisors amp canines no diastema Skull quotDishshapedquot face canine pillar foramen magnum placed anteriorly no sagittal crest on most specimens Postcrania Similar to A afarensis Tools None Habitat Semiarid savanna Australopithecus 39 or Sites South African caves Kromdraai Swartkraans Fossils Many individuals cranial dental amp postcranial remains Dates 18 16 Ma Brain size c 550600 cc Body size Dimorphic females c 30 kg males c 40 kg Teeth Parabolic dental arcade very large molars amp premolars with thick enamel very small incisors amp canines no diastema massive jaws flat tooth wear Skull Low forehead prominent sagittal crest in males flat bony face no canine pillar large supraorbital torus in males flaring zygomatic arch foramen magnum placed anteriorly Postcrania Similar to other Australopithecines bipedal Fingers capable of fine manipulation necessary for tool making Tools Oldowan but Homo present in same cave deposits Habitat Semiarid savanna locally wooded conditions Australopithecus boisei or Paranthropus boisei Sites East African Rift Valley Olduvai Tanzania Koobi Fora amp West Turkana Kenya Fossils Many specimens mostly cranial amp dental OH 5 Olduvai Gorge Bed adult male cranium quotZinjanthropusquot KNMER 406 Adult male cranium KNMER 732 Adult female cranium Dates 18 096 Ma Brain size Small c 400500 cc Body size Very dimorphic maximum 70 kg females c 70 male body weight Teeth Parabolic dental arcade extremely large molars amp premolars with thick enamel extremely small incisors amp canines no diastema very massive jaws flat tooth wear Skull Massive cranium low forehead very prominent sagittal amp nuchal crests flat bony face large subraorbital torus extremely flaring zygomatic arch no canine pillar heartshaped foramen magnum placed anteriorly Postcrania Similar to other Australopithecines bipedal Tools Oldowan but Homo present in same deposits Habitat Semiarid savanna locally wooded conditions Australopithecus aethiopicus or Paranthropus aethiopicus Sites East African Rift Valley West Turkana Kenya Omo Ethiopia Fossils A few relatively complete crania teeth amp jaws KNMWT 17000 quotBlack skullquot adult male cranium KNMWT 17400 juvenile male partial cranium Dates 2624 Ma Body size Similar to A boisei very dimorphic Brain size small c 400 cc Teeth Very large posteriorteeth small anteriorteeth massive jaws third molar smaller than first and second molars flat tooth wear tooth rows converge at rear Skull Very prognathic very flared zygomatics very prominent compound sagittal amp nuchal crests in male flat cranial base heartshaped foramen magnum Postcrania None described Tools None Habitat Semiarid savanna locally wooded conditions Homo habilis Sites East African Rift Valley Olduvai Tanzania Koobi Fora Kenya Fossils Numerous cranial dental amp postcranial specimens OH 7 mandible parietal fragments hand bones OH 8 Nearly complete foot OH 62 Partial skeleton KNMER 1805 KNMER 1813 Partial crania Dates 19 16 Ma Brain size Large gt 600 cc Body size 40 50 kg probably dimorphic Teeth Parabolic dental arcade large incisors amp canines no diastema molars amp premolars smaller than Australopithecus molars amp premolars narrow Skull Thin bones of cranial vault high forehead large braincase no sagittal crest flat bony face small supraorbital torus foramen magnum placed anteriorly Postcrania Long forelimbs hand with apelike features foot with adaptations for climbing Tools Oldowan Habitat Semiarid savanna locally wooded conditions Homo rudolfensis Sites East African Rift Valley Koobi Fora Kenya Fossils Cranial dental amp postcranial specimens KNMER 1470 Nearly complete cranium Date c 19 Ma Brain size Large c 750 cc Body size c 50 kg probably dimorphic Teeth Large incisors amp canines molars amp premolars broad Skull No supraorbital torus face orthognathic not prognathic Postcrania Femur amp foot like later Homo no climbing adaptation Tools None associated with fossils but possibly made Oldowan tools Habitat Semiarid savanna locally wooded conditions Hominid Species Introduction The word quothominidquot refers to members of the family of humans Hominidae which consists of all species on our side of the last common ancestor of humans and living apes Some scientists use a broader definition of Hominidae which includes the great apes Hominids are included in the superfamily of all apes the Hominoidea the members of which are called hominoids Although the hominid fossil record is far from complete and the evidence is often fragmentary there is enough to give a good outline of the evolutionary history of humans The time of the split between humans and living apes used to be thought to have occurred 15 to 20 million years ago or even up to 30 or 40 million years ago Some apes occurring within that time period such as Ramapithecus used to be considered as hominids and possible ancestors of humans Later fossil finds indicated that Ramapithecus was more closely related to the orangutan and new biochemical evidence indicated that the last common ancestor of hominids and apes occurred between 5 and 10 million years ago and probably in the lower end of that range Lewin 1987 Ramapithecus therefore is no longer considered a hominid The field of science which studies the human fossil record is known as paleoanthropology It is the intersection of the disciplines of paleontology the study of ancient lifeforms and anthropology the study of humans Hominid Species The species here are listed roughly in order of appearance in the fossil record note that this ordering is not meant to represent an evolutionary sequence except that the robust australopithecines are kept together Each name consists ofa genus name eg Australopithecus Homo which is always capitalized and a species name eg africanus erectus which is always in lower case Within the text genus names are often omitted for brevity Each species has a type specimen which was used to define it Ardipithecus ramidus This species is a recent discovery announced in September 1994 White et al 1994 Wood 1994 It is the oldest known hominid species dated at 44 million years Most remains are skull fragments Indirect evidence suggests that it was possibly bipedal and that some individuals were about 122 cm 4390quot tall The teeth are intermediate between those of earlier apes and A afarensis but one baby tooth is very primitive resembling a chimpanzee tooth more than any other known hominid tooth Other fossils found with ramidus indicate that it may have been a forest dweller This may cause modification of current theories about why hominids became bipedal which often link bipedalism with a move to a savanna environment White et al have since discovered a skeleton which is 45 complete but have not yet published on it Australopithecus anamensis This species was only named in August 1995 The material consists of 9 fossils mostly found in 1994 from Kanapoi in Kenya and 12 fossils mostly teeth found in 1988 from Allia Bay in Kenya Leakey et al 1995 Anamensis existed between 42 and 39 million years ago and has a mixture of primitive features in the skull and advanced features in the body The teeth and jaws are very similar to those of older fossil apes A partial tibia the larger of the two lower leg bones is strong evidence of bipedalism and a lower humerus the upper arm bone is extremely humanlike Note that although the skull and skeletal bones are thought to be from the same species this is not confirmed Australopithecus afarensis A afarensis existed between 39 and 30 million years ago Afarensis had an apelike face with a low forehead a bony ridge overthe eyes a flat nose and no chin They had protruding jaws with large back teeth Cranial capacity varied from about 375 to 550 cc The skull is similarto that of a chimpanzee except forthe more humanlike teeth The canine teeth are much smaller than those of modern apes but larger and more pointed than those of humans and shape of the jaw is between the rectangular shape of apes and the parabolic shape of humans However their pelvis and leg bones far more closely resemble those of modern man and leave no doubt that they were bipedal although adapted to walking rather than running Leakey 1994 Their bones show that they were physically very strong Females were substantially smaller than males a condition known as sexual dimorphism Height varied between about 107 cm 3396quot and 152 cm 5390quot The finger and toe bones are curved and proportionally longer than in humans but the hands are similar to humans in most other details Johanson and Edey 1981 Most scientists consider this evidence that afarensis was still partially adapted to climbing in trees others consider it evolutionary baggage Australopithecus africanus A africanus existed between 3 and 2 million years ago It is similar to afarensis and was also bipedal but body size was slightly greater Brain size may also have been slightly larger ranging between 420 and 500 cc This is a little larger than chimp brains despite a similar body size but still not advanced in the areas necessary for speech The back teeth were a little bigger than in afarensis Although the teeth and jaws of africanus are much larger than those of humans they are far more similar to human teeth than to those of apes Johanson and Edey 1981 The shape of the jaw is now fully parabolic like that of humans and the size of the canine teeth is further reduced compared to afarensis Australopithecus afarensis and africanus are known as gracile australopithecines because of their relatively lighter build especially in the skull and teeth Gracile means quotslenderquot and in paleoanthropology is used as an antonym to quotrobustquot Despite this they were still more robust than modern humans Australopithecus aethiopicus A aethiopicus existed between 26 and 23 million years ago This species is known from one major specimen the Black Skull discovered by Alan Walker and a few other minor specimens which may belong to the same species It may be an ancestor of robustus and boisei but it has a baffling mixture of primitive and advanced traits The brain size is very small at 410 cc and parts of the skull particularly the hind portions are very primitive most resembling afarensis Other characteristics like the massiveness of the face jaws and single tooth found and the largest sagittal crest in any known hominid are more reminiscent ofA boisei Leakey and Lewin 1992 A sagittal crest is a bony ridge on top of the skull to which chewing muscles attach Australopithecus robustus A robustus had a body similarto that of africanus but a larger and more robust skull and teeth It existed between 2 and 15 million years ago The massive face is flat or dished with no forehead and large brow ridges It has relatively small front teeth but massive grinding teeth in a large lowerjaw Most specimens have sagittal crests lts diet would have been mostly coarse tough food that needed a lot of chewing The average brain size is about 530 cc Bones excavated with robustus skeletons indicate that they may have been used as digging tools Australopithecus boisei was Zinjanthropus boisei A boisei existed between 21 and 11 million years ago It was similar to robustus but the face and cheek teeth were even more massive some molars being up to 2 cm across The brain size is very similar to robustus about 530 cc A few experts consider boisei and robustus to be variants of the same species Australopithecus aethiopicus robustus and boisei are known as robust australopithecines because their skulls in particular are more heavily built Homo habilis H habilis quothandy manquot was so called because of evidence of tools found with its remains Habilis existed between 24 and 15 million years ago It is very similar to australopithecines in many ways The face is still primitive but it projects less than in A africanus The back teeth are smaller but still considerably larger than in modern humans The average brain size at 650 cc is considerably larger than in australopithecines Brain size varies between 500 and 800 cc overlapping the australopithecines at the low end and H erectus at the high end The brain shape is also more humanlike The bulge of Broca39s area essential for speech is visible in one habilis brain cast and indicates it was possibly capable of rudimentary speech Habilis is thought to have been about 127 cm 5390quot tall and about 45 kg 100 lb in weight although females may have been smaller Habilis has been a controversial species Some scientists have not accepted it believing that all habilis specimens should be assigned to either the australopithecines or Homo erectus Many now believe that habilis combines specimens from at least two different Homo species Homo erectus H erectus existed between 18 million and 300000 years ago Like habilis the face has protruding jaws with large molars no chin thick brow ridges and a long low skull with a brain size varying between 750 and 1225 cc Early erectus specimens average about 900 cc while late ones have an average of about 1100 cc Leakey 1994 Some Asian erectus skulls have a sagittal crest The skeleton is more robust than those of modern humans implying greater strength Body proportions vary the Turkana Boy is tall and slender like modern humans from the same area while the few limb bones found of Peking Man indicate a shorter sturdier build Study of the Turkana Boy skeleton indicates that erectus may have been more efficient at walking than modern humans whose skeletons have had to adapt to allow for the birth of largerbrained infants Willis 1989 Homo habilis and all the australopithecines are found only in Africa but erectus was wideranging and has been found in Africa Asia and Europe There is evidence that erectus probably used fire and their stone tools are more sophisticated than those of habilis Homo sapiens archaic Archaic forms of Homo sapiens first appear about 500000 years ago The term covers a diverse group of skulls which have features of both Homo erectus and modern humans The brain size is largerthan erectus and smallerthan most modern humans averaging about 1200 cc and the skull is more rounded than in erectus The skeleton and teeth are usually less robust than erectus but more robust than modern humans Many still have large brow ridges and receding foreheads and chins There is no clear dividing line between late erectus and archaic sapiens and many fossils between 500000 and 200000 years ago are difficult to classify as one or the other Homo sapiens neanderthalensis was Homo neanderthalensis Neandertal man existed between 230000 and 30000 years ago The average brain size is slightly largerthan that of modern humans about 1450 cc but this is probably correlated with their greater bulk The brain case however is longer and lower than that of modern humans with a marked bulge at the back of the skull Like erectus they had a protruding jaw and receding forehead The chin was usually weak The midfacial area also protrudes a feature that is not found in erectus or sapiens and may be an adaptation to cold There are other minor anatomical differences from modern humans the most unusual being some peculiarities of the shoulder blade and of the pubic bone in the pelvis Neandertals mostly lived in cold climates and their body proportions are similar to those of modern coldadapted peoples short and solid with short limbs Men averaged about 168 cm 5396quot in height Their bones are thick and heavy and show signs of powerful muscle attachments Neandertals would have been extraordinarily strong by modern standards and their skeletons show that they endured brutally hard lives A large number of tools and weapons have been found more advanced than those of Homo erectus Neandertals were formidable hunters and are the first people known to have buried their dead with the oldest known burial site being about 100000 years old They are found throughout Europe and the Middle East Western European Neandertals usually have a more robust form and are sometimes called quotclassic Neanderthalsquot Neanderthals found elsewhere tend to be less excessively robust Trinkaus and Shipman 1992 Trinkaus and Howells 1979 Gore 1996 Homo sapiens sapiens modern Modern forms of Homo sapiens first appear about 120000 years ago Modern humans have an average brain size ofabout 1350 cc The forehead rises sharply eyebrow ridges are very small or more usually absent the chin is prominent and the skeleton is very gracile About 40000 years ago with the appearance of the CroMagnon culture tool kitsstarted becoming markedly more sophisticated using a wider variety of raw materials such as bone and antler and containing new implements for making clothing engraving and sculpting Fine artwork in the form of decorated tools beads ivory carvings of humans and animals clay figurines musical instruments and spectacular cave paintings appeared over the next 20000 years Leakey 994 Even within the last 100000 years the longterm trends towards smaller molars and decreased robustness can be discerned The face jaw and teeth of Mesolithic humans about 10000 years ago are about 10 more robust than ours Upper Paleolithic humans about 30000 years ago are about 20 to 30 more robust than the modern condition in Europe and Asia These are considered modern humans although they are sometimes termed quotprimitivequot Interestingly some modern humans aboriginal Australians have tooth sizes more typical of archaic sapiens The smallest tooth sizes are found in those areas where foodprocessing techniques have been used for the longest time This is a probable example of natural selection which has occurred within the last 10000 years Brace 1983 Timeline This diagram shows roughly the times during which each hominid species lived Ages are in millions of years with each character position representing 100000 years This resolution is a little coarse to accurately represent the most modern species Arobustus I A b ei l I Aaethiopicus Aramidus Aanamensis Aafarensis Aafricanus Hhabms MMMMM Herectus Species Australopithecus ramidus Ardipithecus ramidus Australopithecus anamensis Australopithecus afarensis Homo antiquus Australopithecus bahrelghazali Australopithecus africanus Paraustralopithecus aethiopicus Australopithecus aethiopicus Paranthropus robustus Australopithecus robustus Australopithecus walkeri Zinjanthropus boisei Australopithecus boisei Australopithecus crassidens Homo antiquus praegens Australopithecus praegens Homo habilis Pithecanthropus rudolfensis Homo rudolfensis Homo microcranous Homo ergaster Pithecanthropus erectus Homo erectus Homo antecessor Homo heidelbergensis Homo neanderthalensis Homo sapiens archaic Hsapiens Neandertals modern Hsapiens Type Specimen ARAVP 61 KP 29281 LH 4 AL 2881 KT 12H1 Taung Omo 18 TM 1517 KNMWT 17000 OH5 8K6 KNMT1 13150 OH 7 KNMER 1470 KNMER 1813 KNMER 992 Trini 2 ATD65 Mauer 1 Neandertal Named By White et al 1994 M Leakey et al 1995 Johanson et al 1978 Ferguson 1984 Brunet et al 1996 Dart 1925 Arambourg amp Coppens 1968 Broom 1938 Ferguson 1989 L Leakey 1959 Broom 1949 Ferguson 1989 L Leakey et al 1964 Alexeev 1986 Ferguson 1995 Groves amp Mazak 1975 Dubois 1894 Arsuaga et al 1997 Schoetensack 1908 King 1864 Linnaeus 1758 Chapter 4 EVOLUTION IN THE FOSSIL RECORD The fossil record reveals the existence of many creatures that have left no living descendants of great episodes of eXtinction and diversi cation and of the movements of continents and organisms the explain their present distributions The fossil record provides evidence on two particularly important themes 0 Phenotypic transformations in particular lineages 0 Changes in biological diversity over time SOME GEOLOGICAL FUNDAMENTALS ROCK FORMATION EARTH STRUCTURE Radius of 6357 km 3948 miles at the poles and 6378 km 3960 miles at the equator Asthenosphere 0 Inner core 800 miles radius solid iron 0 Outer core1300 miles radius molten iron 0 Mantle 1800 miles radius molten rock Lithosphere 0 Upper part of the mantle o Crust 535 miles thick solid rock ROCK TYPES Igneous solidi ed magma about 65 ofthe crust eg granite lava ows basalt Sedimentary hardened eroded material due to pressure or chemical means about 8 of the crust e g limestone sandstone shale Metamorphic any rock that have undergone further change due to pressure heat and chemical reactions about 27 of the crust e g marble from limestone PLATE TECTONICS The drifting of tectonic plates on the Earth s surface relative to each other It is an ongoing process that has changed the con guration of the continents since their formation in Archean time about This hypothesis rst proposed in 1912 by Alfred Wegener a German Meteorologist was not widely accepted until after 1960 Wegener s evidence for continental drift includes 1 Continental t 2 Glacial deposits indicating high latitudes on portions of the continents that are now in warm latitudes 3 Alignment of geologic features such as mountain belts when continents are reassembled and 4 Occurrence of identical fossils of the same age on landmasses that are no longer connected Other evidence 5 Palaeomagnetism Ferrous material in new igneous rocks becomes magnetized in a direction that depends on the magnetic eld at the time Old rocks in Africa and South America show different magnetic orientation while new rocks show similar orientation The polar pathways of South America and Africa coincide when the two continents are tted together 6 Sea oor spreading due to the molten material emerging at the oceanic ridges and spreading on each side of the ridge The new rocks become magnetized according to the orientation of the magnetic eld prevailing at the time With time magnetic elds change in strength and direction and material become magnetized differently forming similar belts of magnetized rocks on each side of the ridge GEOLOGIC TIME Big Bang Theory Origin of universe between 1520 billion years ago Evidence Hubble and the Red Shift The Expanding Universe Origin of Galaxies and the Solar System Earth Chronology 46 BY earth formed BY billion years 438 BY life originated 35 BY oldest known fossils 25 BY photosynthesis oxygen accumulated 15 BY rst eukaryotes 800 MY softbodies multicellular life MY million years 540 MY hardbodied multicellular life quotArrhenius and graduate student Stephen Mojzsis recently discovered the oldest chemical evidence oflife in sedimentary rocksfrom Greenland The rocks are estimated to be more than 385 billion years old Carbon in these rocks had an isotope pro le seen only in remains of organisms SJ Mojzsis et al Nature 38451 9 I996 quotThe evidence ofthe carbon signatures is crucial in arguing that life on Earth waspresent before 385 billion years ago quot maintains Mojzsis quotFurthermore the carbonaceous matter was found in intimate association with the phosphate mineral apatite a common biologicallyformed substance quot Phosphates exist in cell membranes enzymes genetic material and biological energy molecules quot httpwwwthe scientistcomyr1997marresearch 970331html The Scientist March 31 1997 Absolute ages of geological events can often be determined by radiometric dating which measures the decay of certain radioactive elements in minerals that form in igneous rock The decay of radioactive parent atoms into stable daughter atoms occurs at a constant rate Each radioactive isotope has a speci c halflife eg the halflife of U235 is about 07 billion years Long before radioactivity was discovered geologists had established the relative ages of sedimentary rock formations based on the principle that younger sediments are deposited on top of older ones Layers of sediments deposited at different times are called strata sing Stratum THE GEOLOGIC TIME SCALE Most of the eras and periods of the geologic time scale were named and determined by geologists that did not know about evolution This was done before Darwin s time These eras and period are recognized by their fossil components The time boundaries of the different sectors of the scale are approximations and they change as more information becomes available and with the opinion of the geologists Eras are divided into Periods and those into Epochs The Phanerozoic time is dived into three Eras Paleozoic Mesozoic and Cenozoic l Paleozoic began about 542 My 2 Mesozoic began about 251 My 3 Cenozoic began about 65 My FOSSIL RECORD On the whole the fossil record is very incomplete The record is incomplete for several reasons l Delicate organisms seldom become fossilized or live in environments where decay is rapid 2 Sediments form at intervals and contain only par of the organisms that lived in the region 3 For fossils to form the organisms must rst become solidi ed into rock and rock must survive millions of years without being eroded metamorphosed or subducted and then become accessible to paleontologists 4 Species that evolved elsewhere may appear in a locality after having migrated into the area About 250000 fossil species have been described and represent an estimated 1 at the most of all species that have lived in the past EVOLUTIONARY CHANGES WITHIN THE SPECIES Some records have preserved the changes of a single species These changes tend to be gradual and independent of each other ORIGINS OF HIGHER TAXA THE ORIGINS OF AMPIHBIA The class Sarcopterygii are eXtremely ancient in origin their rst remains appearing in Lower Devonian strata of Germany about 408 million years old The most important group the rhipidistians which gave rise to the amphibians by the end of the Devonian became eXtinct about 120 million years later near the beginning of the Permian Two lesser groups the coelacanths and the dipnoans lung shes have barely survived Recognition of the class Sarcopterygii is controversial in that some ichthyologists believe that the two major groups the Crossopterygii including the rhipidistians and coelacanths and the Dipnoi have arisen from independent origins the present structures of the two groups being widely divergent Osteolepiforms crossopterigians and dipnoans were the rst shes to develop lungs by the end ofthe Devonian 410360 mya By the end of the Devonian 360 mya the transition from rhipidistianosteolepiform sh to tetrapod amphibian had occurred Similarities between early amphibians and osteolepiforms Similar shape and position of dermal skull bones Homologous ns and leg bones Tooth structure similar compleX labyrinthine pulp Sensory lateral line eXtends into the skull of osteolepiforms appear similar and homologous to skull canals of early tetrapods Early amphibians had nrayed caudal tail Similar vertebrae The earliest amphibians on record are Acanthostega and Ichthyostega Both show relationship to rhipidistians o Acanthostega was an early tetrapod that was ill suited for life on land It has internal gills and led an aquatic life 0 Ichthyostega lived in the Late Devonian and had scales and dorsal tail n Advanced traits shared with more advanced amphibians include typical early amphibian limbs and limb supports the lack of gills and strong ribs It used lungs as the primary means to obtain oxygen 0 In Ichthyostega the forelimbs seem to have been weightbearing but the forearm was unable to eXtend fully Only one articulated specimen shows a femur in association with a body and forequarters The shoulders were massive compared with the much smaller and paddlelike hind limb in contrast to the more conventional proportions that it is usually given 0 The proportions of an elephant seal appear the closest analogue among living animals Perhaps Ichthyostega hauled itself up shelving beaches moving its forelimbs in parallel and dragging its hindquarters along Clack 1997 ORIGIN OF BIRDS Birds may have evolved from bipedal grounddwelling endothermic reptiles their feathers derived from scales The rst protobirds probably evolved in the Late Jurassic from a group of theropod dinosaurs related to the Coelosaurians The only lineage of endothermic archosaurs to survive into the Cenozoic were the Neornithes or quotmodern birdsquot The two most primitive birds accepted by most scientists are ArchaeopteryX and Confuciusornis ArchaeopteryX and the 30 million year younger Confuciusomis have several traits in common 0 They both have three claws on their Wings 0 The ngers are not fused o The wishbone is almost identical and the breastbone is small There are also some traits that separate them 0 The tail is longer in ArchaeopteryX while the claws are stronger in Confuciusornis o ArchaeopteryX has teeth while Confuciusomis has a beak ARCHAEOPTERYX The rst feathered fossil from the Upper Jurassic 150 mya 0 Found in limestone from Bavaria Very similar to reptiles Feathers It could y although weakly Light bones and were fast and agile Long slender necks large back legs and long counter balancing tails Bipedal stance Birds show some characters that were present in early dinosaurs and then were lost eg wis one quotDinosaurs had a strong wishbone in theirprimitive state but had lost it through evolution In the early 1900 s anatomists most notably Gerhard Hellman in 1926 refused to believe that an animal could recall a lostpart ofit s anatomy They said that birds could not have been descended from dinosaurs because dinosaurs had already lost their wishbone and that any similarities between coelurosaurs and birds was the result ofevolutionary convergence Recent finds have shown that a number ofthe coelurosaurs had re evolved collarbones Norman 1994 Studies have shown that a suppresser gene prevents a primitive gene from expressing itself When that gene does not work the older trait expresses itself There are many examples where a suppresser gene does not work and it can be seen even today From time to time a healthy human baby is born with a tailprotrudingfrom it Whales have been hauled in withfully developed legs sticking out ofthe side ofits boay a throwback to a time when they were land borne predators The most unusual example is ofa birdfrom South America known as a Hoatzin As a chick it shows a wing structure remarkably similar toArchaeopteryx It has claws on its wings that it uses to climb up and down in thefoliage to escape predators fits wing is placed next to an Archaeopteryx specimen the similarities are striking This bird has recalled a primitive traitfrom genetic storage andNatural Selection has acted upon it to the point where it has re established itself This trait enables the chick to have a better chance ofsurviving to adulthood where the wing bonesfuse and look like any other birds Bakker 1986quot httpwwu micro uteer coursesmcmurrvspr39 0 77 in tin html Confuciusomis was found in Liaoning Province China and is between 120140 million years old 0 Confuciusomis is the earliest known bird that could y well Its wings were rather crude but it was equipped with features seen in today s birds such as lightweight bones and a shorter rudderlike tail 0 It had a toothless beak CaudipteryX zoui is another intermediate species from China from the Middle Cretaceous 120 mya It was a fast runner with feathers but incapable of ight Ichthyornis and Hesperornis were Late Cretaceous birds that had teeth like ArchaeopteryX but show several more advanced features These two species resemble modern seabirds in their anatomy Both of these species had Deep set teeth that curved backwards indicating a sh diet Ichthyornis had a wide crest to support its ight muscles but it more closely resembled that of a dinosaur than a bird 0 It also had at dinosaur style joints in its vertebrae 0 Both of these birds had lost the long tailed trait of the dinosaurs in favor of the modern parson s nose style of today s birds 0 These birds supported a pattern from dinosaur to primitive bird to more modern ones to fully modern ones 0 Source httpwww mirrn nte as 39 39 quotn 71 instin html Next feathered fossils come from the Cretaceous about 110 million years later and they are mostly shorebirds Feathers o No record of when and how they evolved eg scales 0 Were they primarily for insulation or for ying 0 Did they develop in arboreal reptiles for gliding or in ground dwelling animals for running faster cursorial Archaeopteryx had feathers very similar to the primary ying feathers of modern birds Sinosauropteryx had body feathers but their function is unknown their function could have been for insulation Bird evolution moved fast from the Cretaceous through the beginning of the Tertiary and modern features appeared o Fused bones enlarge keeled sternum increase brain size loss of teeth loss of claws in the hands There is no clear reason why modern birds do not have teeth One hypothesis is that the reduction and modi cation of forelimbs for ight did not allowed the birds to manipulate food into the proper position in the mouth eg head rst for swallowing Then the teeth disappeared and the beak a large scale on top of the mouth evolved By the Oligocene 55 mya most modern bird orders had appeared ORIGIN OF MAMMALS Mammalian characteristics evolved mostly during the Mesozoic era 24565 mya Mesozoic era consists of the Triassic 245208 mya Jurassic 208146 mya and Cretaceous 14065 mya periods Characteristics Softbody parts Mammary glands Live birth except for monotremes Hair covering and sweat glands to control temperature endotherms Diaphragm to increase inspiration of oxygen Fourchambered heart Expansion of the neocortex greater intelligence 094395 Skeletal features Double occipital condyle for articulation with the rst vertebra Mandible consisting of a single bone Single nasal opening in the skull Ear ossicles derived from the reptilian quadrate and articular bones Bony secondary palate Large braincase Heterodont dentition greater differentiation among teeth 99wwr Soon after the rst amniotes originated in the Carboniferous they gave rise to the Synapsida a group characterized by an opening called temporal fenestra behind the eye socket whic probably provided space for enlarged jaw muscles to eXpand into when contracted Synapsid reptiles rst appeared in the Carboniferous Strong evidence indicates that pelycosaurs synapsids are close to the line that gave rise to the therapsids Pelycosaurs appeared before the dinosaurs The primitive mammallike reptiles the Pelycosauria became eXtinct during the Permian They left behind a variety of advanced mammallike reptiles collectively termed the Therapsida By the Permian 290245 mya they had evolved into therapsids synapsids primarily adapted to a terrestrial eXistence Therapsids are often called quotmammalianlike reptilesquot Permian synapsids in the order Therapsida had large canine teeth and the center of the palate was recessed suggesting that the breathing passage was partially separated from the mouth cavity their hind legs were rather vertical more like mammals than reptiles The therapsids show a chain of evolutionary steps towards mammals Differentiated teeth and skull development Jaw articulation consolidation of the jaw bones Development of mammal ear bones palate pelvis consolidation scapula with spine and leg positioning By the early Triassic 245208 mya some therapsids had become endotherrns Cynodonts were an advanced group of therapsids that arose in the very late Permian The skeleton of cynodont therapsids was mammallike and distinct from that of other reptiles 0 Vertical stance knees pointing forward elbows pointing backward o The jaw articulation was still reptilian 0 Later therapsids had a mandible entirely composed of dentary bone It s here that we rst see a secondary palate Cheek teeth had multiple cusps Two occipital condyles Vast expansion of the temporal fenestra with a great deal of transmission of jaw musculature Development of specialized teeth heterodont dentition Teeth developed cusps for chewing Mammals have to breathe continuously even when eating this necessity developed the bony palate and separates air entering the pharynx from food being chewed in the mouth In amphibians and terrestrial reptiles the nasal openings are in the anterior portion of the mouth and the animal has to temporarily interrupt breathing while the mouth is full of food Two of the great innovations of Cynodonts which lead directly to mammals are the development of occlusion and single replacement of teeth ie two sets Occlusion the meeting of molars and premolars to grind over one another to process food more ef ciently Single replacement two sets of teeth probably to ensure accurate occlusion and suckling Morganucodont was almost a mammal with typical mammalian teeth and a lower jaw composed almost entirely of the dentary The jaw had a double articulation with the skull o The articulation of the quadrate and articular bones together with the stapes closely approach the condition in modern mammals in which these bones transmit sound to the inner ear The recently described Hadrocodium Luo et al 2001 from the Jurassic is almost a mammal o The articular and quadrate bones are separated from the lower jaw and fully lodge in the middle ear 0 The lower jaw consists fully of the dentary The fossil record shows that mammalian characters evolved gradually ORIGIN OF THE CETACEA Whales and dolphins form the Order Cetacea and evolved from terrestrial forms Their closest living relatives among the mammals are hippopotamuses this is based on molecular evidence Some zoologists think that they should be included in the Order Artiodactyla together with the pigs camels and ruminants cows and antelopes Living cetaceans are highly modi ed mammals adapted to aquatic life Characteristics of the Cetacea l Uniquely shaped tympanic bone that completely encloses the ear 2 A nasal opening far back on top of the skull 3 Stiff elbow wrist and nger joints all enclosed in a paddlelike ipper 4 Rudimentary pelvis and hind limbs disconnected from the pelvis 5 Lack of fused differentiated sacral vertebrae that land mammals have 6 Toothed whales have a large cavity in the lower jaw the foramen that contains a sound transmitting pad of fat C 39D neral stages of the evolution of the cetaceans o ElomeryX hippolike artiodactyl resembling the probable ancestor of the cetaceans o Pakicetus 5348 My probably semiaquatic with a tympanic bone resembling that of modern cetaceans o Ambulocetus 4847 My adapted to living in shallow coastal waters used its legs for swimming digits end in small hooves like those of artiodactyls mandibular foramen larger than in pakicetids predator with long jaws o Rodhocetus 4939 My swam in its hind legs fusion of sacral vertebrae was reduced the pelvis was weak and could not support the animal on land tooth form was simpler nasal opening was farther back from the tip of the snout o Dorudon 35 My was fully aquatic and used the tail for propulsion the nonfunctional pelvis was disconnected from the vertebral column and the hind limb barely projected from the body teeth are simpler nostril is far back in the skull front limbs are ipper like with almost in exible wrist and elbow 0 Modern harbor porpoise blowhole is far back on the top of the head accounting for the peculiar shape of the head have no residual hind limbs THE HOMININ FOSSIL RECORD The closest relatives to humans are the chimpanzees The term hominin has been applied to the sister group of the chimpanzees The evolution of modern humans show through many intermediates from apelike ancestors There is disagreement about how many species and genera of hominins should be recognized because 0 Fossil specimens are too few and too widely separated in time and space 0 Many differences are quantitative differences in degrees and often rather slight so it is dif cult to determine which species is ancestral or collateral to the ancestral one The overall pattern of evolution is clear but the speci c phylogenetic relationship between the taxa is not In the late Miocene about 8 mya the homininae chimps gorillas and humans split from other apes 0 Supported by molecular data There is no agreement about the time when humans and chimps split data varies between 77 and 35 mya o 35 55 mya divergence proposed by Sarich and Cronin 1976 55 77 mya proposed by Sibley and Alquist 1984 in Chapter 12 o 49 mya is strongly supported by eXtensive molecular studies done by Horai et al 1995 Sahelanthropus tchadensis from the late Miocene 6 7 7 My is most primitive known hominin 0 Small canines 0 Flat face 0 Almost certainly bipedal Orrorin tugenensis lived about 6 Mya Ardipithecus kadabba about 52 58 My old Ardipithecus ramidus lived about 45 43 Mya in what is now Ethiopia Australopithecus anamensis is about 42 7 39 My old Kenyanthropus platyops is about 35 My old Australopithecus afarensis 35 My old had the following primitive characteristics 0 Prognathism Long arms and legs Large canines Small brain Curved bones in ngers and toes for climbing trees And the following advanced characteristics 0 Pelvis and hind limbs are for walking upright it was a bipedal animal In the Pliocene 53 Mya and Pleistocene 18 Mya the number of hominin species was probably very diverse Australopithecus africanus 30 7 25 Mya had large molars and premolars adapted for powerful chewing they probably fed on tubers and coarse plant material A africanus had greater brain capacity than A afarensis The increased cranial capacity is noted by the change in genus designation from Australopithecus to Homo Homo habilis was small slightly more than chimp sized but with cranial capacities of 600800 cc increased blood vessels in the head and brain and increased exibility of ngers and wrists o The earliest fossils assigned to the genus Homo are 19 7 15 Mya late Pliocene and early Pleistocene They are variable enough to be assigned to three species H habilis H ergaster and H rudolfensis The oldest specimens are similar to A africanus and the younger one intergraded gradually with Homo erectus Limbs retain the apelike proportions but the structure of the leg and foot that its bipedal locomotion was like that of humans H habilis is associated with stone tools and cut animal bones Olduwan technology Homo erectus lived from about 16 Mya to 200000 years ago Most authorities think that habilis erectus and sapiens are a single evolutionary lineage Face became more vertical with a less projectedjaw The skull is rounded Teeth are smaller Cranial capacity is between 800 to 1100 cm3 By about 18 mya erectus had migrated out of Africa into Asia and speci cally to Java Approximately 1 mya the tool kits begin to include teardrop shaped hand axes and cleavers of uniform proportions These tools are found throughout Africa and Europe but not in Asia Homo erectus fossils persist until about 05 mya At that point skeletal changes including increasing cranial capacity prompt a change in species name to Archaic Homo sapiens These fossils are often subdivided into several subspecies such as rhodesiensis in Africa and neandertalensis in Europe and the middle east Neandertals are considered by some authorities as a separate species of Homo Homo neanderthalensis Neanderthals had cranial capacities of about 1600 cc modern humans average 1400 cc but with skulls that sloped back from the brow ridges and with a pronounced bulge at the back of the skull They were big game hunters who survived from about 300000 BC to 35000 BC Their skeletons show an increasing divergence from the gracile body plan of the other Homo species as they were adapted to the frequent glacial stages of Europe during this time Neandertals coexisted with modern Homo sapiens in the Middle East from about 80000 BC to about 40000 BC and in Europe from about 45000 BC to 35000 BC We find the first evidence of intentional burials sometimes with grave goods among neandertalensis We also find evidence of individuals who were crippled during their lifetimes yet were cared for and lived on for years with significant handicaps Modern Homo sapiens skeletons appear in Africa between 200000 and 100000 BP 0 In the Middle East excavations at Skhul cave have also provided evidence of early Homo sapiens o The tool kits they used began to include blades with length twice the width struck off of cores 0 We nd the earliest preservation of evidence of artistic expression among modern H sapiens in the form of beads carvings and cave paintings 0 Tool kits also begin to vary more rapidly from region to region and through shorter periods of time The Upper Paleolithic culture emerged about 40000 years ago and several cultural styles appeared successively in Europe eg Aurignacian and Mousterian Selfadornment art mythical and religious beliefs become more evident after 35000 years ago Agriculture appeared about 11000 to 10000 years ago It is unknown at present if these cultural advances were associated with genetic changes PHYLOGENY AND THE FOSSIL RECORD There is a correlation between the relative times of origin of taxa as inferred from phylogenetic analysis and their relative times of appearance in the fossil record This correspondence is imperfect o Imperfect fossil record 0 A group that originated in the distant past might be recovered only from recent deposits 0 An ancient lineage may have acquired the diagnostic characters much later The sequence in which the fossils appears match phylogeny EVOLUTIONARY TRENDS The fossil record shows many evolutionary trends In many cases those trends show a reversal to an earlier form Some features may have never reverted because they advantageous or even necessary Eg Feathers of penguins remain because they are insulating and are used in sexual displays in penguins and ostriches respectively The notochord has not disappeared because it induces the development of the central nervous system Some cases may be truly irreversible because the developmental foundation of some characters has been lost in evolution Dollo s Law complex characters once lost are not regained Many lineages often pass through similar stages called grades This generalization is called Cope s Rule PUNCTUATED EQUILIBRIA Gradual transition from one form to another is not always found in the fossil record Intermediate stages in the evolution of higher taxa are often unknown These gaps are usually eXplained by the incompleteness of the fossil record Eldredge and Gould proposed in 1972 a new eXplanation o Punctuated equilibrium short periods of rapid change and macroevolutionary events during which new taxa arise speciation interrupt long periods of little change called stasis This hypothesis contrasts with the one called phyletic gradualism the traditional hypothesis that proposes a gradual change over a long period of time The fossil record offers examples of both punctuated equilibrium and phyletic gradualism The hypothesis proposed by Eldredge and Gould is based on the model known as founder effect speciation or peripatric speciation proposed by Ernst Mayr in 1954 o A new species appears suddenly in the fossil record because they evolved in small populations separated from the ancestral species and then fully formed migrated in the region where the fossil samples were taken The evolutionary change may have been gradual but rapid and offstage Eldredge and Gould also proposed that changes in morphology occur is association with the evolution of new species speciation This hypothesis is not widely accepted because it seems to contradict fossil record evidence 0 The fossil record shown that characters may evolved in between longstable states in populations that do not undergo speciation o This pattern has been called punctuated gradualism RATES OF EVOLUTION The rate of evolutionary change varies greatly between characters among evolving lineages and with the same lineage over time Individual features typically display a low rate of evolution averaged over long periods of time but more detailed fossil records show rapid shortterm uctuations in characters Scientists often use the unit called the Haldane to measure the mean change of a character per generation 0 The haldane is a measure of the evolutionary change using the number of standard deviation by which a character mean changes per generation 0 Standard deviation is a measure of the amount of variation within a population When rates of character evolution have been measured for ancestordescendant series of dated fossils the most striking result has been that average rates of evolution are usually eXtremely low 0 Measurements show a average rate of change over a long period of time Longterm averages conceal rapid evolutionary rates if the rate uctuates or if the character uctuates rapidly but show little net change 0 Fluctuation refers to long periods of no change alternate with bursts of rapid change We would eXpect higher rates if the measurements are made over shorter intervals of time Evolutionary rates can be very rapid but they are not sustained at high rates for very long Chapter 10 GENETIC DRIFT EVOLUTION AT RANDOM Purposes and goals are unique to human thought Natural phenomena do not have purpose Scientists use chance or randomness to mean that when physical causes can result in any of several outcomes scientists cannot predict what the outcome will be in any particular case Scientists may b e able to specify the probability and thus the frequency of one or another outcome Genetic drift and natural selection are the two most important causes of allele substitution 7 evolutionary change 7 in populations A sequence of random events in succession can change the frequency of an allele this is called random genetic drift 0 Allele frequency is changed from one generation to the neXt allele uctuation o The genes in one generation do not end up in the same ratio in the neXt generation 0 This is a case of nonadaptive evolution genetic drift does not necessarily results in adaptation We should not assume that a characteristic or a difference between populations and species is adaptive or has evolved by natural selection unless there is evidence for this conclusion THE THEORY OF GENETIC DRIFT GENETIC DRIFT AS SAMPLING ERROR The genes included in any generation whether in newly formed zygotes or in offspring that survive to reproduce are a sample of the genes carried by the previous generation Any sample is subject to random variation or sampling error The proportions of different kinds of items in a sample are likely to differ by chance from the proportions in the set of items from which the sample is drawn Over long periods of time variation is more easily maintained in large populations than in small ones Random genetic drift reduces variation and leads eventually to the random xation of one allele and the loss of other unless it is countered by other processes such as gene ow or mutation COALESCENCE Not all members of a generation leave equal number of descendants Some do not leave any As time goes on more and more alleles of a particular gene become eXtinct so that the population consists of descendants of fewer and fewer of the original gene copies Eventually all gene copies in the population are descended form a single ancestral gene copy The genes in the present population have coalesced back to a single common ancestor The smaller the population the more rapidly all gene copies coalesce back to a single ancestral copy A population will eventually become monomorphic for one allele or the other and that the probability that one allele will be xed rather than the other is equal to the initial frequency of that allele 0 A1 08 the probability of A1 to become xed is 80 0 A2 02 the probability of A2 to become xed is 20 In genetics coalescent theory states that all genes or alleles in a given population are ultimately inherited from a single ancestor shared by all members of the population known as the most recent common ancestor If the inheritance relationships are written in the form of a phylogenetic tree termed a gene genealogy the gene or allele of interest is said to undergo coalescence to the common ancestor Coalescent theory seeks to reconstruct the ancestral relationship of individuals and is therefore of great utility in 39 g the 1 1 39 1 39 1 39l ofspecies based on information at the molecular level httpenwikipediaorgwikiCoalescent theoLV This does not mean that the population of a single common ancestor had only one member at that time This model does not include the evolution of adaptive traits those that evolve by natural selection RANDOM FLUCTUATIONS IN ALLELE FREQUENCIES Small independent populations of a species are called demes and the grouping of all these population is a metapopulation An allele is selectively neutral if selection neither favors it or not Neutral alleles may change by mutation over time allowing the calculations of the molecular clock Example ofrandom fluctuation of an allele A deme has an allele frequency of 05 in the next generation the frequency may be 047 in the following generation it will change again from 047 to some other higher or lower value This process of random uctuation continues over time Since no stabilizing force returns the allele to 05 the frequency will wander drift to either 0 or 1 the allele is either extinct or fixed Once an allele has reached either 0 or 1 it cannot change unless another allele is introduced into the population either by mutation or by gene ow from another population The allele frequency may increase in some demes of the metapopulation and decrease in some others The variance in allele frequency among the demes continues to increase from generation to generation The number of demes xed for on or another allele continues to increase until all demes have become xed Thus demes that initially are genetically identical evolve by chance to have different genetic constitutions EVOLUTION BY GENETIC DRIFT 1 Allele frequency uctuates at random within a population and eventually one or the other becomes 1xe 2 Genetic variation at a locus declines and eventually is lost The frequency of heterozygotes declines At any time an allele s probability of xation equals its frequency at that time and is not affected or predicted by its previous history of change in frequency 4 Populations with the same initial allele frequency diverge An allele just arisen by mutation and represented by only one among the 2N copies in the population its frequency is p 12N and this is the likelihood of reaching a frequency of l 6 Evolution by genetic drift proceeds faster in small than in large populations Since the allele frequency in each deme changes eventually becoming 0 or 1 the frequency of heterozygotes declines to zero in each deme and in the metapopulation as a whole W U gt1 EFFECTIVE POPULATION SIZE In many populations the number counted Census Size may be greater than the number that actually contributes genes to the neXt generation 0 Elephant seals wolves The rate of genetic drift of allele frequencies and of loss of heterozygosity will be greater than eXpected from the population s census size The effective size Ne of an actual population is the number of individuals in an ideal population in which every adult reproduces in which the rate of genetic drift measured by the decline 0 heterozygosity is the same as it would be in the actual population 0 The effective population size is the number of individuals in a population that contribute to the neXt generation 0 The effective population size is actually smaller than the census or absolute population Reasons 1 Variation in the number of progeny produced by females males or both reduces Ne 2 A seX ratio different from 11 lowers the effective population size 3 Natural selection can lower Ne eg some individuals contribute more gene copies than others 4 Generation overlap or inbreeding when offspring mate with parent generation the pair carries identical copies of the same genes the number of genes propagated is reduced 5 Fluctuation in population size Smaller populations are more affected than larger populations FOUNDER EFFECT Population bottlenecks occur when a population is reduced for at least one generation Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans in icted on them in the 18905 Hunting reduced their population size to as few as 20 individuals at the end of the 19th century Their population has since rebounded to over 300007but their genes still carry the marks of this bottleneck they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted httn39 evolution herkelev 39 quot html The genetic drift that occurs when a new population is established by few colonists is called founder effect The founder effect was de ned by Ernst Mayr in 1963 The founders carry only a small fraction of the genes found in the original population There is a loss of genetic variation The new population will be genetically different from the parent population the frequency of genes will be different In some cases it may lead to speciation For example the Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists Today the Afrikaner population has an unusually high frequency of the gene that causes Huntington s disease because those original Dutch colonists just happened to carry that gene with unusually high frequency This effect is easy to recognize in genetic diseases but of course the frequencies of all sorts of genes are affected by founder events httn39 evnlnti on herkelev 39 quotn html GENETIC DRIFT IN REAL POPULATION S Laboratory populations Experiment by Peter Buri 1956 Started 107 experimental populations of Drosophila melanogaster with 8 males and 8 females Followed the allele bw and 1m for eye color by which all three genotypes are recognized Propagated each population for 19 generations By generation 19 30 populations had lost the 1m allele and 28 had become xed for it Among the un xed l 39 39 39 quot allele f l 39 were quite evenly distributed The results matched those expected by the genetic drift theory Other experiments conducted by McCommas and Bryant 1990 with house ies also supports the mathematical predictions of the genetic drift theory Four populations of house ies were established at each three bottleneck sizes 1 4 and 16 pairs Each population rapidly increased to 1000 individuals after which the populations were reduced to same bottleneck size The procedure was repeated ve times The average heterozygosity decline steadily after each bottleneck The smaller the bottlenecks were the more rapidly it declined Natural populations Theories tell us what patterns to expect in the genetic features of natural populations We infer the causes of evolution by interpreting these patterns Patterns of molecular genetic variation in natural populations often correspond to what we would expect if the loci were affected by genetic drift Fixation of deleterious alleles can reduce survival and reproduction increasing the risk of extinction THE NEUTRAL THEORY OF MOLECULAR EVOLUTION Neutral alleles are not subject to natural selection because they do not affect or have very little effect on tness The neutral theory of molecular evolution is that most evolutionary change at the molecular level is driven by random drift rather than natural selection The neutral theory does not suggest that random drift explains all evolutionary change natural selection is still needed to explain adaptation However the neutral theory states that evolution at the level of the DNA and proteins but not of morphology is dominated by random processes most evolution at the molecular level would then be nonadaptive The neutral theory can be contrasted with the idea that almost all molecular evolution has been driven by natural selection Source httpwww quot quot 39 com ridle turur39 evolution and neutral thenrv a n Proposed by Motoo Kimura in the late 1960s and early 1970s Small minority of mutations in DNA or protein sequences is advantageous and become xed by natural selection 0 Many mutations are disadvantageous and become eliminated by natural selection The great majority of mutations that are xed do not affect tness 7 they are neutral gt Silent or synonymous mutations 0 Neutral mutations are xed by genetic drift because natural selection does not act on it Additional explanations httpenwikipediaorgwikiNeutral theog of molecular evolution httprlarwin eeh m nnn 48190 e The neutral theory of molecular evolution also proposes that o Evolutionary substitutions at the molecular level proceed at a roughly constant rate 0 So that the degree of sequence difference between species can serve as a molecular clock 0 It is possible to determine the divergence time of species large parts of nonproteincoding DNA sequences are highly conserved under strong purifying selection and thus do not vary much from individual to individual indicating that mutations in these regions have deleterious consequencesl lQ1 When genetic variation does not result in differences in tness selection cannot directly affect the frequency of such variation As a result the genetic variation at those sites will be higher than at sites where variation does in uence tness 7 7Rice SH 2004 Evolutionary Theory Mathematical and Conceptual Foundations Sinauer Associates Sunderland Massachusetts USA ISBN 0878937021 See ch 1 19 Kryukov GV Schmidt S amp Sunyaev S 2005 Small tness effect of mutations in highly conserved noncoding regions Human Molecular Genetics 1422219 2 Bejerano G Pheasant M Makuninl Stephen S Kent WJ Mattick J S amp Haussler D 2004 Ultraconserved elements in the human genome Science 30413215 Source http enwikipedia orgwikiNaturaliselection PRINCIPLES OF THE NEUTRAL THEORY Only a fraction of the mutations that occur is effectively neutral The neutral mutation rate uo will be less than the total mutation rate up Effectively neutral means that the mutant allele is so similar to the original one that in its effect on survival and reproduction that changes in its frequency are governed by genetic drift alone not by natural selection If the mutation affects tness to some slight extent then natural selection and genetic drift will operate simultaneously on the frequency of the mutant allele The majority of the mutations will be deleterious if the protein encoded by the gene cannot be altered without seriously affecting its function and the neutral mutation rate will be much lower This locus is said to have many functional constraints Highest mutation rate will be at the thirdbasepair position within regions that code for proteins and lowest at the secondbasepair position because these places have the highest and lowest redundancy DNA sequences that are not transcribed and have no known function such introns and pseudogenes would have less or no constraints and therefore the neutral mutation rate will be the highest Applying the principles of the neutral theory the following can be calculated knowing the size of the effective population Ne and the rate of mutation per gamete per generation uo 0 Average number of new mutations 0 Probability that a mutation will be xed by genetic drift 0 Number of neutral mutations that arise in a given generation and will someday be xed Therefore the same number of neutral mutations should be xed in every generation the rate of xation of mutations is theoretically constant and equals the neutral mutation rate 0 The neutral theory predicts that over long spans of time substitutions will occur at an approximately constant rate for a given gene providing a basis for the molecular clock From the above data the number of generations that have passed since the divergence from a common ancestor of two species can be estimated As time passes multiple or successive substitutions in the same locus causes the observed number of differences between species to be less than the number of substitutions that have occurred 0 A a C a T a A it will appear that A has not mutated when in fact it has mutated three times The Debate The debate is not about whether natural selection operates or not 1 Some evolutionary biologists prefer the neutral theory to be the null hypothesis to explain genetic variation within species or populations Adaptation and natural selection should be the preferred explanation only if genetic drift cannot explain the data The neutral theory has replaced natural selection with randomness in most cases of mutation 2 There is so much evidence that natural selection has shaped species characteristics selection should be the explanation of choice The neutral theory should be the preferred explanation only if natural selection cannot explain the data What percentage of the alleles is neutral versus those that are nonneutral VARIATION WITHIN AND AMONG SPECIES The fraction of mutations that are neutral is higher for synonymous than for nonsynonymous amino acidreplacing nucleotide substitutions A study by McDonald and Kreitman 1991 showed that 5 of the polymorphisms but fully 29 of the substitutions that distinguish species are replacement changes They concluded that amino acid replacing substitutions is an adaptive process governed by natural selection If most replacement substitutions are advantageous rather than neutral they will increase in frequency and be xed more rapidly than by genetic drift alone Replacement substitutions will spend less time in the polymorphic state than selectively neutral synonymous substitutions do They will contribute less to polymorphic variation Within species PROTEINS often di er in aminoacid sequence across species This di erence has evolved by the accumulation of neutral mutations by random drift the xation of adaptive mutations by selection or a mixture of the two Here we propose a simple statistical test of the neutral protein evolution hypothesis based on a comparison of the number of aminoacid replacement substitutions to synonymous substitutions in the coding region of a locus If the observed substitutions are neutral the ratio of replacement to synonymous xed di brences between species should be the same as the ratio of replacement to synonymous polymorphisms within species DAM sequence data on the Adh locus encoding alcohol dehydrogenase EC 1111 in three species in the Drosophila melanogaster species subgroup do not fit this expectation instead there are more xed replacement di brences between species than expected We suggest that these excess replacement substitutions result from adaptive xation of selectively advantageous mutations Adaptive protein evolution at the Adh locus in Drosophila by John H McDonald amp Martin Kreitman Nature 351 652654 20 June 1991 data from Drosophila simulans and D yakuba We estimate that 45 of all aminoacid substitutions have been xed by natural selection and that on average one adaptive substitution occurs every 45 years in these species Adaptive protein evolution in Drosophila by Nick G C Smith and Adam EyreWalker Nature 415 10221024 28 Feb 2002 DO COMPARISONS AMONG SPECIES SUPPORT THE NEUTRAL THEORY Sequencing DNA has provided data on the rate of molecular evolution Most DNA sequence evolution has been neutral 1 Rate of synonymous substitutions is generally greater than the rate of replacement substitutions e g various genes of humans versus rodents 2 Substitution occurs most frequently at thirdbase position in codons and least frequently in second base positions 3 Rates of substitutions are higher in introns than in coding regions of the same gene and even higher in pseudogenes o Pseudogenes are nonfunctional genes related in sequence to functional genes 4 Some genes evolve more slowly than other e g histone genes 0 Genes that evolve most slowly are those thought to be most strongly constrained by their precise function The rate of evolution is greatest at DNA positions that when altered are least likely to affect function and therefore least likely to alter the organism s tness Support for the neutral theory s prediction that the rate of evolution should be constant is equivocal 0 Some rates have been constant and others not 0 Mitochondrial DNA sequences have evolved more slowly in turtles than in other vertebrates GENE FLOW AND GENETIC DRIFT Gene ow or gene migration is the transfer of alleles from one population to another The rate at which populations drift toward xation of one allele or another is inversely proportional to the effective population size Gene ow counteracts gene xation The mathematical model page 241 shows that a little gene ow keeps all the demes fairly similar in allele frequency and heterozygosity remains high Genetic drift and gene ow affect all loci the same way whereas natural selection affects different loci more or less independently If each of a number of polymorphic loci yields about the same value of gene frequency it is likely that selection is not strong GENE TREES AND POPULATION HISTORY The genealogical history of genes in populations is the basis of Coalescent Theory Because gene lineages within a population become eXtinct by chance over the course of time all gene copies in a population today are descended from one gene copy that eXisted at some time in the past The smaller the effective size of a population the more rapidly genetic drift transpires The eXisting gene copies in a small population must stem from a more recent common ancestor than the gene copies in a large population It takes longer for the present genes in the larger population to coalesce to their common ancestor In a diploid population the common ancestor of a random pair of gene copies occurred 2Ne generations ago where Ne is the size of the effective population THE ORIGIN OF MODERN H 0M0 SAPIENS REVISITED Homo erectus migrated from Africa to Europe and Asia about 18 million years ago H erectus evolved there into Homo neanderthalensis and archaic Homo sapiens There is considerable evidence that modern Homo sapiens a separate species evolved in Africa and spread from there about 100000 years ago replacing archaic Homo sapiens without interbreeding with them to any great eXtent Mitochondrial DNA provides the evidence that supports the replacemen or outof Africa hypothesis There are several mtDNA lineages in Africa There are far fewer nucleotide differences among nonAfrican haplotypes on average than among African haplotypes Several studies have concluded that all human mitochondrial genes both African and nonAfrican are descended from a common ancestral gene that eXisted 156000 to 250000 years ago This does not mean that the human population at that time consisted of one man and one woman it means only that all other 39 39 39 39 and Y 39 in the l l 39 39 at that time have failed to leaf descendants Similar conclusions were reached in analyses of Y chromosome sequences and Autosomal microsatellite loci Supporting evidence synthesizes new genetic archaeological climatic and linguistic discoveries Genetic diversity amongst modern human populations is greatest in the African continent There are 15 surviving mtDNA lineages in Africa which date back more than 80000 years compared with only one for the rest of the world 0 This population probably consisted of a breeding population between 4600 and 11200 individuals Three distinct African populations can be determined genetically on the basis of the L0 mutation in mtDNA aligning with ethnic linguistic and now archaeological evidence 1 mtDNA Q Ychromosome haplogroup A M91 The Khoisan speakers the modern Hadza of Tanzania and the Bushmen San and Khoikhoi once called quotHottentotquot populations 2 mtDNA Q SS95000 yrs ago Y chr E M60 began 5060000 yrs ago This population adopted cultural innovations suitable for rainforest and woodland zones 0 The West African genomes of the Niger Congo and Nilo Saharan speaking peoples led to the evolution of the Ivory and West Africa and modern Bantu populations 0 Also sharing the Y chr B mtDNA L2 are the smaller groups surviving in the Congo rainforests the Mbuti and Bayaka pygmy peoples of the Ituri and other Congo rainforests 3 mtDNA Q Human populations similar to those found at Ngaloba and Laetoli in East Africa and dated to 5969000 years before the present 0 All other groups of human probably descended from this group Source httpenwikipediaorgwikiOut of Africa theory HUMAN EVOLUTION SUMMARY The position of humans within the taxonomy is as follows Class Mammalia Subclass Theria Infraclass Eutheria Order Primates Suborder Anthropoidea Infraorder Catarrhini Superfamily Hominoidea Family Hominidae Genus Homo Species sapiens A more complete picture of where Homo sapiens stand in the grander scheme of things can be found below Some terms that may need de ning are Catarrhini infraorder Old World Monkeys Platyrrhini infraorder New World Monkeys Pongidae family Chimpanzees gorillas and orangutans Hylobatidae family Gibbons Pan genus chimpanzees Pongo genus orangutans EARLY PRIMATES Aegyptopithecus late Oligocene 2829 mya Proconsul 23 14 mya Three species major africanus and nyanzae Kenyapithecus wickeri 14 mya Pierolapithecus catalaunicus 13 million years ago during the Miocene HOMINIDS Sahelanthropus tchadensis from the late Miocene 6 7 7 my is most primitive known hominin Orrorin tugenensis lived about 6 Mya Ardipithecus kadabba about 52 58 my old Ardipithecus ramidus lived about 45 43 Mya in what is now Ethiopia Australopithecus anamensis is about 42 7 39 my old Kenyanthropus platyops is about 35 my old AUSTRALOPITHECINES GRACILE GROUP Australopithecus anamensis 42 to 35mya Australopithecus afarensis 35 mya Australopithecus africanus 23 mya ROBUST GROUP Paranthropus Australopithecus aethiopicus 33 to 26 mya Paranthropus Australopithecus boisei 26 mya to 12 mya Paranthropus Australopithecus robustus 26 mya to 18 mya HOMO rudolfensis 25 mya to 18mya 2 habilis 16 mya to 2 mya ergaster 2 mya erectus 800000 to 400000 ya antecessor 10 mya 2 to 800 tya 16 heidelbergensis 600000 to 250000 ya neanderthalensis 230000 to 29000 ya sapiens Early Modems 200000 ya to 50000 2 sapiens Cro Magnon 50000 ya to present httgenwikigediaorgwikiTimeline of human evolution Chapter 11 NATURAL SELECTION AND ADAPTATION An adaptation is a characteristic that enhances the survival or reproduction of organisms that have it The members of the population become better suited to some feature of their environment through change in a characteristic that affects their survival or reproduction ADAPTATIONS IN ACTION SOME EXAMPLES Philodendron and other aroids produce two kinds of leaves adapted to different environments small leaves for the dark forest oor and growth toward the dark looking for a tree trunk to climb and large leaves with long petioles to catch sunlight in the upper regions of the forest canopy Equot Pseudocopulatory pollination in orchids Several species of orchids have modi ed ower parts to look somewhat like a female insect and the ower emits a scent that mimics the attractive seX pheromone of a female bee y or thynnine wasp depending on the orchid species The ower is pollinated in the process of copulation the insect does not derive any bene t from this activity W The skull bones of most terrestrial vertebrates are rigidly attached to one another but in snakes they are loosely joined They swallow their prey by drawing it into a gullet with recurved teeth mounted on a number of freely moving bones that act as levers and fulcrums operated by compleX muscles 5 Australian arboreal weaver ants construct nests of living leaves by the intricately coordinated action of numerous workers groups of which draw together the edges of leaves by grasping one leaf in their mandible while clinging to one anther THE NATURE OF NATURAL SELECTION Most adaptations are compleX and appear to be constructed to perform a certain function eg growth feeding pollination etc The process of natural selection is random and mindless 0 Those with variations that enhance survival and reproduction replace those less suited who reproduce to a lesser eXtent Adaptive biological processes appear to have goals but there is no conscious anticipation of the future in cells The future cannot cause material events in the present This apparent purpose is caused by the operation of a program coded or prearranged information residing in DNA sequences that controls a process DEFINITIONS OF NATURAL SELECTION Survival is a prerequisite for reproduction Fitness is often de ned as reproductive success The components of tness are 1 Probability of survival to reproductive age 2 Average number of offspring produced via female function 3 Average number of offspring produced via male function Sexual selection is based on competition for mates It can be considered a form of natural selection The probability of survival and the average number of offspring enter into the de nition of tness and these concepts apply only to groups of events Natural selection eXists if there is an average difference in reproductive success Differences in survival and reproduction eXist among individual organisms among genes and among populations and species Different kinds of biological entities may vary in tness resulting in different levels of selection 0 The difference among traits that affect tness Natural selection may occur among genes individual organisms and groups such as populations or species Selection has an evolutionary effect only if there is inheritance Natural selection is a name for statistical differences in reproductive success among genes organisms or populations NATURAL SELECTION AND CHANCE Neutral alleles are not affected by natural selection because they do not affect reproductive success quotff biases quotff in 39 39 quot39 of 39 39 success 1 r Fitness differences are average Natural selection is a consistent difference in tness among phenotypically different biological entities and is the antithesis of chance It is not possible to tell if difference in reproductive success between two individuals is due to tness or to chance SELECTION OF AND SELECTION FOR Natural selection may select for a certain body size mating behavior or other feature There may incidental selection of other features that are correlated with those features In speaking of a function of a feature it is implied that there has been natural selection of organisms with that feature and of genes that program it but for the feature itself A feature may have other effects or consequences that were not its function and for which there was not selection EXPERIMENTAL STUDIES OF NATURAL SELECTION Look over these examples on pages 252 to 257 Bacterial populations Inversion polymorphism in Drosophila Male reproductive success Population size in flour beetles Sel sh genetic elements LEVELS OF SELECTION SELECTION OF ORGANISMS AND GROUPS Sociobiology is the biological basis of social behavior in animals 0 Eg ocking parental care territoriality courtship dominance cooperation etc Altruism is doing good for others 0 Eg sharing food warning of danger adopting orphans etc There is always cost to altruistic behavior It raises the genetic tness of another individual while lowering its own How can altruistic traits be maintained in a population when the altruistic gene is selected against Altruistic trait cannot evolve by individual selection An altruistic genotype amid other genotypes that were not altruistic would necessarily decline in frequency simply because it would leave fewer offspring per capita than the others If a population were to consist of altruistic genotypes a sel sh mutant 7 a cheater 7 would increase to xation Statements about organisms acting against their own good for quotthe good of the speciesquot are probably wrong Kin selection has been proposed as a mechanism for the evolution of altruistic behavior 0 Proposed by William Hamilton in 1964 Kin selection is selection at the level of the gene Either the individual or its immediate relatives leave behind many offspring The altruist s relatives are more likely to carry copies of the altruistic allele than are members of the population at random When the altruist s enhances the tness of its relative even at some cost to its own tness it can increase the frequency of the allele 0 Genes reach the next generation via relatives As far as evolution is concerned it makes no difference what animals passed the quotgoodquot genes to the next generation the actor or its siblings Kin selection also explains eusociality Division of labor The sterile castes give up tness entirely and devout their efforts to the good of the colony Cooperative caring of the young Overlap of at least two generations of life stages able to contribute to the colony s wellbeing The colony is in fact a family made mostly of the queen and her offspring It is found in bees wasps and termites and one mammal the naked mole rat of Africa SPECIES SELECTION Species selection is the process responsible for the proliferation of species that have lower extinction and higher speciation rates It refers to a differential rate of extinction and speciation due to some characteristic of the species such as geographic isolation or allele frequency Differential speciation Some lineages have higher speciation rate than other related lineages o For example orchids family Orchidaceae with about 19500species have highly modi ed owers to attract specialized pollinators and have produced more species over time than its close relative the iris family Iridaceae which consists of about 1750 species There has a differential speciation in this case caused by the ower type and the attraction of pollinators Differential extinction also occurs asexual forms have a higher rate of extinction than sexual forms Many groups of plants and animals have give rise to asexually reproducing lineages but also all such lineages are very young as indicated by their very close genetic similarity to sexual forms Asexual forms that arose long time ago have not persisted THE NATURE OF ADAPTATIONS DEFINITIONS OF ADAPTATION Adaptations can be de ned from the point of view of its present effect in increasing the tness of an individual A characteristic body part shape or behavior that helps a plant or animal survive in its environment www reefededuauglossagahtml Adaptation can also be de ned from the historical perspective of it phylogenetic origin A biological adaptation is an anatomical structure physiological process or behavioral trait of an organism that has evolved over a period of time by the process of natural selection such that it increases the expected longterm reproductive success of the organism enwikipediaorgwikiAdaptation biology The presence of a particular feature versus another may be due to adaptation or phylogenetic history Preadaptation is a feature that by chance serves another function the swim bladder of rhipidistian sh became the lung of early amphibians An exaptation is an adaptation that performs a new function different from the original function performed when the adaptation arose through natural selection 0 Wings of penguins and alcids are used for swimming rather than ying RECOGNIZING ADAPTATION S Not all traits are adaptations A trait 1 May be the consequence of physics or chemistry e g the red color of the blood 2 May have arisen through genetic drift rather natural selection 3 May have evolved not because of particular advantage but because it is correlated to another feature that was advantageous e g pleiotropy Several methods may be used to infer if a feature is an adaptation 1 Complexity cannot evolve except by natural selection 2 Design of a feature corresponds to its function 0 Functional morphology and ecological physiology study how the design of features allows organism to survive and function in an ecological setting 0 The relation of morphological variation and functional morphology to environmental change Ecological physiologists identify the physiological adaptations of organisms and organ systems investigate the molecular cellular and physiological mechanisms underlying these adaptations and determine how these adaptations affect growth reproduction movement survival and other basic biological characteristics of organisms and their ecological role in communities UC Santa Barbara Santa Barbara CA 93106 httn39 vawlife ci 110 h 39 39 I phvsiologvhtml 3 Experiments may show that a feature enhances survival or reproduction in a way the increases tness relative to individuals in which the feature is modi ed or absent 4 The comparative method consists of comparing sets of species to pose or test hypotheses on adaptation and other evolutionary phenomena o Convergent evolution A feature that evolves independently in many lineages because of a similar selection pressure E g the similar beak of birds that feed on nectar appeared in six different lineages o Phylogenetic information may be necessary in some cases for the proper use of the comparative met 0 WHAT NO TO EXPECT OF NATURAL SELECTION AND ADAPTATION Natural selection does not necessarily produce anything that ca be called evolutionary progress Necessity of adaptation Not all environmental changes reduce population size Ar1 environmental change that does not threaten extinction may set up selection for change in some characteristics New adaptations may evolve in and unchanging environment if new mutations arise that are superior to the previously existing one Perfection Selection may x only those genetic variants with a higher tness than other genetic variants in that population at that time Selection cannot x the best of all conceivable variants if they do not arise the best possible variants may fall short of perfection because of various kinds of constraints Progress Evolution does not have goals Measurement of improvement or efficiency must be relevant to each species special niche or task Harmony and the balance ofnature Selection at the level of genes and individual organisms is inherently sel sh the gene or genotype with the highest rate of increase increases at the expense of other individuals Cooperative behavior can be explained by kin selection Kin selection does not work across species boundaries natural selection cannot produce any modi cation in a species exclusively for the good of another species Mutualistic relationships between species consist of mutual exploitation The equilibrium observed in ecological communities does not re ect any striving for harmony Morality and ethics Natural selection is the name for differences among organisms or genes in reproductive success Natural selection cannot be described as moral or immoral just or unjust kind or cruel Hence it cannot be used as a justi cation or model for human morality or ethics Neither the evolutionary theory nor any other eld of science can speak of or nd eVidence of morality or immorality Science describes what it is not what ought to be The naturalistic fallacy the supposition that what is natural is necessarily good has not legitimate philosophical foundation
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