The barometer below shows the level of mercury at a given atmosphericpressure. Fill all the other barometers with mercuryfor that same atmospheric pressure. Explain your answer.
Primate Adaptive Trends Primates are Mammals ● Ancestral Homologies: Features primates share with other placental mammals ○ Mammary Glands produce milk to nourish young ○ Homeothermy, fur for insulation, sweat glands ○ Heterodonty (incisors, canines, premolars, molars) ○ Expansion of the neocortex (outer most region of the brain) of the brain ■ spacial reasoning, memory, planning, and (in humans) language ○ Placenta, nourishes fetus during gestation, allows for a more efficient exchange of nutrients to the fetus during gestation, at the end of this mammals give birth to offspring that are at a more advanced stage in development compared to other vertebrates, long gestations followed by live birth ○ Maternal Care of their young What Defines the Order Primates/How do we deal with the variation of Primates ● Within the order of primates we have two major subdivisions, the Strepsirhini and the Haplorhini (More detail on these to follow in next week’s lecture) ● The difficulty in defining primates lies in the difference in characteristic expression between the two suborders ● One characteristic that is universally present in all primates is petrosal bulla ○ Part of the bony underside of the skull, encloses, houses, and protects the middle ear ● A lot of the traits of primates come from their original argorial environment—trees and forests ● The Order Primates ○ Derived Homologies ■ Petrosal bulla ■ High degree of grasping ability in the hands and feet ■ Primates as a group have an opposable thumb ■ Opposable big toe as well, with the one exception being ourselves as our big toe is brought back into line with the rest of our foot ■ Most primates have nails instead of claws ■ Sensitive tactile pads with skin ridges on the tips of the digits ■ folds increase surface area, more surface area to place nerve endings and also adds for more friction when grasping ■ Decreased reliance on olfaction (smell) particularly in haplorhines ■ Olfactory regions of the brain are reduced ■ Haplorhine primates have a significantly higher percentage of pseudogenes among the olfactory receptor gene family than do other mammals; this trend is especially pronounced in humans ■ Nasal structures of the skull are reduced ■ Haplorhines lack a moist naked skin (rhinarium) surrounding the nostrils ■ soft tissue around the nose that is always covered with a film of secretion and it essentially functions as a wind protector that can detect the evaporation of the secretion and detects that as wind and movement to ultimately sense a predator around and the smell of a predator ■ Stereoscopic vision and enhanced depth perception ■ Haplorhines have evolved trichromatic color vision ■ rods perceive differences in light intensity, cones distinguish differences in the wavelengths of the light which we perceive as differences in color ■ Why this is important ■ Being able to tell the difference between what foods are edible and what aren’t, specifically fruits which are a large part of primates diets ■ Being able to distinguish between young leaves and old leaves, young leaves being much more nutrient packed than old leaves and important in the diet ■ Facial coloration for recognition of species, facial expression communication ■ Binocular vision ■ Frontal visual fields ■ Primate brains are wired differently, such that the information from the right side gets processed in the left side of the brain and vice versa, wired to compute paralax ■ paralax the displacement in the position of an object viewed by the right and left eye ■ Need this wiring in order to perceive depth in the way we do ■ Forward facing eyes with an enclosed bony orbit (postorbital bar) ■ Large brain relative to body size, expanded neocortex, throughout all stages of development ■ Prolonged life history, single offspring ■ Primates develop slowly and invest heavily in offspring ■ Give birth to single offspring, with some exceptions and invest heavily in them ■ Longer gestation ■ Longer infancy and juvenile periods, and delayed reproductive maturation ■ Long Lifespan ■ Relatively slow lives compared to many other mammals ■ period of time separating births between chimps in 35 years, whereas other species are reproductively mature earlier and have more kids ■ Primates are social ■ Learn from group mates: one reason for that long childhood ■ Maintain close social bonds ■ Social hierarchy that is constructed and learning how to navigate it ■ suggested that we need a long period of time to learn the social skills in order to be successful as adults ○ Ancestral Homologies ■ Generalized body plan ■ Retention of the collar bone (clavicle) ■ Two separate bones in lower arm (ulna and radius) ■ Five digestive the hands and feet ■ Generalized dentition ■ Heterodonty ● Dental adaptation: ○ Carnivores: high pointed cusps for tearing meat ○ Elephants: broad flat surfaces on cheek teeth for chewing tough grasses and plant materials ○ Primates: low, rounded cusps; generalized dentition that allows them to process most types of food ● Generalized features of the primate dentition (features shared with other mammals) ○ teeth in the upper dn lower jaw ○ bilaterally symmetric ○ heterodont dentition (incisors, canines, premolars and molars) ■ incisors cut good ■ canines tear food, also behavioral functions for aggressive behavior in fights ■ posterior teeth: chewing ■ premolars and molars are for crushing and grinding ■ anterior teeth are for ingestion ○ Dental adaptation for different diets ■ insectivory (insect eating) ■ sharp create for puncturing the outer skeleton of insects ■ folivory (leaf eating) ■ well developed shearing crests for cutting tough leafy material into small pieces ■ frugivory (fruit eating) ■ low cusps for crushing soft fruit Primate Diversity Primates Strepsirrhine Haplorrhine Lemuroidea Lorisoidea Tarsier Platyrrhine Catarhine Cerropithucoidea Hominoidea Primate Behavior ● Socioecological Model ○ Rooted in the fact that there is asymmetry in the reproductive investment of males and females in their offspring, they differ in how much they invest and how ■ more variability into who and what males invest in their offspring ○ Females are influenced mostly by the distribution of food because they have to support not only themselves but their offspring ■ Where and how the food is distributed determines what kind of social groups females can form depending on what kind of competition they will be dealing with ● Primate Diets ○ Must provide the energy required to regulate essential bodily functions, and to sustain growth, development and reproduction ■ Must provide specific types of nutrients ■ Amino acids and proteins ■ Fats and oils ■ Carbohydrates ■ Vitamins, minerals, and elements ■ Must minimize exposure to toxins ■ toxins are often concentrated in mature leaves ands seeds ■ young leaves, fruits and flowers tend to have lower concentrations of toxins ■ Primates obtain nutrients from many different sources ■ Carbohydrates from fruit and gums ■ Fats and oils from animal prey such as insects, also nuts and seeds ■ Protein from insect and animal prey, and young leaves ■ Leaves are also high in fiber, which can be difficult to digest ■ Most colobines eat leaves and have enlarged intestines ○ Most primates rely more heavily on some types of foods than others ■ Frugivore, folivore, insectivore, gummivore ■ Insectivores tend to be smaller in body size ■ Smaller animals have relatively higher energy requirements and eat small amounts of high quality foods ■ Folivores tend to be larger in body size ■ Can afford to eat large quantities of lower quality foods ○ Diets influence ranging patterns ■ Leaves are more abundant in supply and predictable in space and time ■ Fruits tend to be less predictable in supply and patchily distributed in space and time ■ Folivores tend to have smaller home ranges than Frugivores ■ Costsand benefits of territoriality ■ Benefit: prevents outsiders from exploiting the limited resources within a territory ■ Cost: energetically costly ● Why Do Primates Live in Groups ■ Costs of sociality ■ greater competition for resources ■ vulnerability to infectious disease ■ Two main benefits of sociality ■ Enhanced access to resources ■ Reduced vulnerability to predation ■ Two main models of Sociality ■ 1. Resource Defense Model ■ Primates live in groups because groups are more successful in defending access to resources than lone individuals ■ Join defense of food resources if profitable when: ■ (1) Food items are relatively valuable ■ (2) Food sources are clumped in space and time ■ (3) There is enough food within defended patches to meet the needs of several individuals ■ Fruit often meets these three requirements ■ Larger groups generally are more successful in fights over resources than small groups ■ Problems: ■ Benefits gained in between group competition are offset by costs incurred from increased within group competition for food resources ■ Does not explain the social organization of certain species that do not concentrate on fruit ■ 2. Predator Defense Model ■ Group living evolved as a defense against predators ■ A wide array of predators hunt primates, and predation is thought to be a significant source of mortality among wild primates ■ Grouping may reduce vulnerability to predation ■ Terrestrial species tend to form larger groups than arboreal species ■ Solitary haplorhines (e.g. orangutans, spider monkeys) are large in body size and apparently face little danger from predators ■ Juveniles suffer from higher mortality in smaller groups than in larger groups ■ Primates seem to adjust their behavior in response to the risk of predation (e.g. alarm calling) ■ Weaknesses of model: ■ Predation is very difficult to observe and it is therefore difficult to establish whether it is clearly linked to group size ● Reproductive Asymmetry ○ Primate mothers are almost always the primary (if not exclusive) caretakers of offspring ○ The behavior of fathers is much more variable ■ father will never exclusively be the caretaker of the offspring because of the time of lactation ○ Reproductive Potential= the maximum number of offspring an individual can produce ■ Female reproductive potential is more limited ■ Females born with limited # of ova (eggs) ■ Female can only breed when ova mature and are released ■ Male reproductive potential is very high ■ Sperm ar smaller and more numerous ■ Constantly replenished ■ Males can fertilize whenever sperm are replenished; more often ○ Female strategies ■ Other limits on reproductive potential ■ Energetic costs of pregnancy and lactation requires mammalian females to make a significant initial investment in each offspring ■ Each infant represents a significant portion of a female’s lifetime fitness ■ Females have limited capacity to increase reproductive success by increasing # of offspring ■ Females are best able to increase reproductive success by increasing chances of survival ■ Females can improve likelihood of their and their offspring’s survival in 2 ways: ■ (1) Invest more care and energy into offspring ■ Depends largely on her ability to obtain important resources (food, nest sites, helpers) to support herself and her offspring ■ (2) Be choosy about males fathering offspring ■ only mate with quality males ■ Female reproductive success is limited primarily by access to important resources necessary for survival ■ Female strategies are primarily influenced by the distribution of food ■ Female relationships are influenced by competitive regimes, which are consequence of food patch size and distribution ■ (1) Scramble Competition ■ Occurs when resources cannot be easily monopolized or defended and therefore access occurs on a firstcome firstserve basis ■ resources of low value are highly dispersed ■ ex. leaves ■ (2) Contest Competition ■ Occurs when access to a resource can be monopolized by one of more individuals; some individuals systematically exclude others, and obtain more of the resources ■ Resource patches are clumped, of immediate size and high value ■ ex. fruits ■ Fission Fusion Societies ■ Group size and composition vary over time ■ Benefits of grouping ■ Mitigate costs of within group competition ■ Dominance ■ Often measured in terms of the direction of approachretreat interactions, or the direction of submissive and aggressive behaviors in interactions ■ When there is competition, dominance rank may determine priority of access to preferred resources ■ Dominance rank has significant fitness consequences ■ Offspring of highranking females are large for age (faster growth rates) and have earlier ages at maturity ■ Begin reproducing earlier —> may have an additional offspring compared to lowerranking females ■ Offspring of highranking females are more likely to survive, have earlier ages at maturity, and shorter inter birth intervals ○ Male Strategies ■ What limits reproductive potential ■ For most mammals, the main limiting factor for male reproductive success is the number of females he can mate with ■ High variance in reproductive success among males (reproductive skew) ■ There is high variance in reproductive success among males ■ Leads to competition among males ■ Males can increase reproductive success by increasing the number of mates ■ They do this through competition with other males to gain access to mates ■ Because females are a limited resource, being “choosy” isn’t the best option for males to increase RS in most species ■ male reproductive success is limited primarily by the availability of mating opportunities ■ Male strategies are primarily influenced by the distribution of fertile females ■ Contrast among males is more violent than those of females because their is more at stake ○ Sexual Selection ■ A form of natural selection that occurs when individuals differ in their ability to compete with others for mates or to attract members of the opposite sex ■ Favors the evolution of traits that allow the limited sex (males in most species) to compete more effectively for access to the limiting sex (females) ■ Darwin: Differences in reproductive success caused by competition over mates —> sexual selection ■ “Sexual selection…depends, not on a struggle for existence, but on a struggle between males for possession of females; the result is not death of unsuccessful competition, but few offspring." ■ Intersexual Selection ■ Where individuals exert choice among individuals of the opposite sex for mating partners ■ favors traits that make males (usually) more attractive to females ■ Favors traits that: ■ (1) Provide direct benefits to their mates ■ (2) Indicate good genes and thus increase the fitness of the offspring ■ (3) Make males more conspicuous to females (although they can be maladaptive) ■ Potentially problematic as these traits make males more conspicuous when it comes to their predators ■ Intrasexual Selection ■ Competition among same sex individuals for access to members of the opposite sex ■ Favors large body size, large canine teeth, and other traits that enhance competitive ability ■ Contest Competition for mats —> traits that improve fighting success ■ Selection for large male size —> body size sexual dimorphism ■ Selection for large male canine size —> canine dimorphism ■ Sexual dimorphism ■ when males and females differ consistently in size or appearance ■ greatest in onemale multi female (polygynous) social groups ■ Least in monogamous social groups ■ Sperm Competition ■ In social systems where multiple males have access and malemale competition is high, sexual selection favors sperm competition ■ Increased sperm production (testes size) ■ Infanticide ■ Act of killing a dependent infant ■ One male, multi female structure are most common to have this ■ Outsider males overthrow resident dominant male, and a new leader male is established ■ This may be followed by killing got unweaned infants by the new leader male ■ Sexual Selection Hypothesis: Infanticide is a male reproductive tactic which is sexuallyelected (i.e., evolved as a consequence of malemale competition) ■ Predictions: ■ Infant killing will be directed at unrelated offspring, thereby reducing the RS of competition males by killing their infants ■ Death of the dependent infant will lead to a termination of lactation; mother becomes fertile sooner ■ The killer increases his chances of mating with the mother and siring the next infant ■ DNA analysis supports the adaptive hypothesis in langurs ■ In all cases with complete DNA samples ,the attacker male could be excluded as the father of the victim ■ IN all cases, of subsequent births, the presumed killer was the likely father of the subsequent infant. ■ Primates choose mates based on MHC diversity ■ Rhesus Macaques ■ Males that were heterozygous at a MHC locus sired significantly more offspring than homozygous males —> increased fitness ■ PigTailed Macaques ■ Similarity in MHC antigens between mother and father predicts pregnancy loss ■ Females also exert choice based on dominance ■ Capuchin Monkeys ■ Females exert choice for dominant males —> direct more grooming, sexual solicitations, maintain proximity towards highranking males ■ Baboons: MaleFemale “friendships" ■ Close associations between females and adult males; preferential mating when the female is fertile ■ Suggested to provide protection of the female, and protection of the infant from infanticide ■ Human Mate Choice ■ Symmetry: Honest indicator of the quality of someone’s genes ■ Honest signal: information increases offspring fitness ■ Humans select mates on the basis of odor cues, which indicate genetic diversity at important immune function loci Fossils ● Fossils The surviving bones and teeth of a once living animal; fundamental source of date, primary source of date, tells a lot about behavior, environment, etc. ○ Preserved remains of onceliving organisms ○ How they are formed: ■ Hominid dies, often times footprints are left in the mud ■ With time, only bones remain ■ Skeleton is broken by trampling ■ Skeleton and footprints are buried by water and sediment ■ Over time, more sediments accumulate and bones fossilize ■ Erosion exposes the layer of strata containing the bones and footprints ● Paleontology The study of extinct organisms based on their fossilized remains ○ Where was it found, what kind of environment was it found, what other species were around at the time and how might they have been related ● What is a fossil ○ Fossilization is a rare event ○ Several conditions must be met before remains can be preserved: ■ Remains must be suitable for fossilization ■ Remains must be buried ■ The material in which the remains are buried must be suitable for fossilization ● What can we learn from fossils ○ Look at cranial size and shape and predict cognition and behavior ○ Look at the teeth and make predictions of diet, behavior, and social structure ○ Measure body proportions to learn something about possible environment and ecology ○ Look at the pelvis to predict obstetrics and locomotion ○ Morphology of the hands to look at manual dexterity ○ Morphology of lower limbs to reconstruct something about locomotion and substrate ● Bias in the fossil record ○ The fossil record is not a complete record of the history of organisms ever to exist on earth; it is only a sample of the plants and animals that once lived ○ Some skeletal parts preserve better than others, *GO BACK* ● Some unusual surprises ○ Footprints (Laetoli, Tanzania) ■ Individual walked across a volcanic ash layer ■ Soft rain cemented the footprints, and they were covered by another ash deposit ■ Information about locomotion ○ Coprolites (fossilized feces) ■ More common when individuals incorporate inorganic components into their diets (e.g. hyenas eat bones) ■ Useful to understand diet and environment ● The Matrix ○ Skeletons become fossils by absorbing minerals from their surroundings ○ The matrix composition is informative for analyzing fossils and its is critical for the dating got fossils ○ Context is critical ■ Want to be able to associate the bones you are excavating with the sediments they were in to look at this to understand environment, humidity, weather, etc. ● Dating Fossils ○ Relative Dating focused on being able to figure out which sediments are older than other sediments, and how they relate ■ Lithostratigraphy use characteristics of the rock layers to link sedimentary sequences and establish relative ages across sites ■ Biostratigraphy using organisms themselves esp. index fossils to establish relative ages across sites ■ mapping their date of first appearance and then disappearance ■ especially helpful when organisms are wide ranging and if they are a short lived organism ■ Tephrostratigraphy Using chemical similarities of volcanic ash layers to determine time equivalence across sites ■ especially important in east Africa which was an area of very active volcanism during an important stretch of our ancestral history ■ different volcanoes produce different chemical signatures, which when compared can allow us to determine time equivalence between different sites ■ Paleomagnetism using changes in the earth’s magnetic polarity to establish age ■ Earth’s magnetic polarity has changed in the past ■ Establishes a broad geological context. Uses principles of stratigraphy (=study of rock layers) to establish the relative ages between localities and between fossils founding these localities ■ Law of Superpositions: basically that higher layers are the newest rocks and the lower layers are the oldest layers, in the absence of other geological or tectonic processes ○ Chronometric (absolute) Dating allow you to put an absolute time frame on ■ techniques that estimate the age of a fossil in absolute terms, through he use of a natural ‘clock’ such as radioactive decay ■ Isotopoic/radiometric ■ Isotopes: variations of the same element, which differ in their molecular weight ■ When an organism dies, unstable isotopes decay into stable isotopes at a predictable rate ■ This rate (or halflife) can be used to determine the time elapsed since the animal died ■ Different methods are useful to date different spans of time ■ The most suitable method in each situation depends on the elements and materials that are found in a site and on their halflife ■ CDating ■ good for younger samples ■ KAr dating ■ Uranium series dating ■ these are both better for older samples ■ Electron Trap methods ■ Thermoluminescence ■ Opticallystimulated luminescence ■ Electron spin resonance ○ Each of these methods have degrees of error so we combine them to try to get the best estimate of year Primate Origins Continental Drift ● Earth’s crust is formed by continental plates that float and move on the plastic mantle ● ● Position of continents has changed throughout time ● (1) Position of the continents influence the movement and distribution of animal species, including primates ● (2) Distribution of continents influence climate Recognizing early fossil primates ● Petrosal Bulla ● Highly Derived Hands and Feet ○ Grasping hands and feet ○ Flat nails instead of claws ● Decreased reliance on smell ○ Reduction of the snout ● Increased reliance on vision ○ Forward facing eyes ○ Protected eyes (postorbital bar) Adaptive Origins of Primates ● Hypothesis: ○ Arboreal ■ Primate characteristics such as grasping hands and feet, nails, and stereoscopic vision evolved as adaptations to the arboreal lifestyle of early primate ancestors ■ BUT: Primate ancestors were already arboreal so arboreality alone is not enough to explain primate adaptations ■ Many other extant arboreal mammals lack primate specializations ■ Arboreality alone can’t fully explain distinctive primate traits ■ opossum, squirrel, raccoon, tree shrew ○ Visual Predation ■ Primate visual specializations and other distinctive primate traits, evolved as adaptations for stalking and grasping insect prey in the terminal branches of trees ■ Reduction of olfaction would be a secondary result of the orbits coming together ■ Attempts to link the visual specializations in viewing prey with depth perception in being accurate in targeting prey in an arboreal environment, in the terminal branches of trees ○ Angiosperm Exploitation ■ Primates coevolved in concert with the adaptive radiation of flowering plants to exploit their products (fruits, flowers, nectar) and the insects that feed on them in a small branch setting ■ This links the evolution of primates in the beginning of the cenozoic area with the appearance of angiosperms or flower breeding plants ■ Environment that was much warmer than is it today, thought to have been a period of recovery from the comet impact killing off much of the plant life before it, before that period the prominent plant were gymnosperms that are exposed seeds such as pine trees with their pine cones ■ around this time that flowering plants appeared (angiosperms) ■ with these, insects that act as pollinators also appeared ■ In other words, all of a sudden on the landscape you have new resources to be exploited —> the flowers, the fruits, the insects ■ This hypothesis thus proposes that primates would have co evolved to exploit these newly found resources ■ Visual adaptation according the this was based on the necessary ability to distinguish between colorful fruits and flowers as well as the insects within the canopy ● Consensus view incorporates ideas from the visual predation model and the angiosperm exploitation model ● Consistent with fossil evidence showing that earliest primates were nocturnal and had adaptations for being insectivorous and fruiteating Evolution of Primates: Family Tree ● Paleocene (6555 million years ago/mya) ○ Earliest record of primates in fossil record from the paleocene comes from Plesiadapiforms ■ Primitive, they retain a number of ancestral mammalian traits ■ Some plesiadapiforms possessed some, but not all, derived primate traits ■ Not clear if they fall within or just outside of the primate evolutionary tree ● Eocene (5534 mya) ○ First Primates of “Modern Aspect" ○ Adapoids ■ Elongated snout ■ Many were diurnal (small orbits) ■ Lack derived features of strepsirhines of haplorhines ■ Probably ancestral to strepsirrhines ○ Omomyoids ■ Short snout ■ Large orbits suggest nocturnality ■ Small, primarily insectivorous ■ Possible relationship with haplorhines ● Oligocene (2435 mya) ○ First evidence of anthropoid primates ○ Marked cooling and drying grand at the end of the Eocene ○ Extinction of certain species and evolution of new ones ○ Geographic distribution of early fossil anthropoids ○ Found in the Fayum (in Egypt) very rich fossil depository ■ at least fourteen different species of anthropoids were found here ○ Genus Apidium ■ Small bodied arboreal quadrupedal ■ Small brain ■ Diurnal ■ 22.214.171.124 dental formula —> indicative of its evolutionary position before NW monkeys divergence ○ The arrival of the New World Monkeys in South America ■ (1) Ancestors of NW monkeys originated in Africa and rafted across the Atlantic Ocean ■ (2) Ancestors of NW monkeys can be North American primates (but no fossils support this hypothesis) ○ Genus Aegyptopithecus ■ Medium sized, arboreal ■ Diurnal ■ Frugivorous ■ Small Brain ■ Derived Catarrhine dental formula ■ Loss of the 2nd premolar, for a dental formula of 126.96.36.199 ■ Postdates divergence of New World monkeys and shares affinities with Old World monkeys ● Miocene (255 mya) ○ Earliest encounter with apes ○ Extant Apes ■ Locomotion underneath branches (large size) —> corresponding post cranial adaptations ■ Apes swing below branches ■ No tail, long flexible arms, more vertical posture, larger brains ○ Ape Localities today apes show a more limited geographic distribution ■ All diversity we saw in the miocene has been limited to 4 main species today because of limited geographic locations ○ Ape Diversity ■ Approximately 100 ape species during the Miocene ■ In Europe, Asia, and Africa ■ Examples of some of these species: ■ Early African Morotopithecus and Proconsul ■ 20 Million years ago, Uganda, Kenya, Namibia ■ Good evidence that this group originated in Africa because the earliest Miocene forms were found in Africa ■ Derived Hominoid Features: ■ Larger relative brain size ■ Shorter snout compared to Aegyptopithecus ■ Y5 Molars ■ A lot of scientists like to call Miocenes Dentist apes because a lot of what links them together is their dental makeup ■ lacked a tail ■ The post cranial skeleton indicates Proconsul was quadrupedal and lacked derived features for suspensory locomotion ■ Good candidates to represent the last common ancestor of apes and humans ■ Asian forms, Sivapithecus ■ Late Miocene: 1218 million years ago ■ Many features of the skull suggest a close evolutionary relationship with orangutans ■ Post cranium suggests quadrupedal locomotion ■ Hominoid Diversity: Gigantopithecus ■ 9 mya 100,000 years ago Nepal, China, India, Vietnam ■ Largest primate that has ever existed: 10 ft ■ Coexisted with H. erectus for some time ○ Evolutionary History of the Apes ■ Many different species, with unclear evolutionary relationships ■ Sivapithecus or similar forms likely ancestors of orangutans ■ Some European and Asian species might be ancestral to African apes ○ Decline of Miocene Hominoids ■ Climate changes in the late Miocene (cooler and dryer climate) ■ Too slow generation time and developmental period to deal with these climatic changes ■ With significant climate changes between the birth of apes, because of the slow developmental time it is much more difficult to deal with these climatic influences ■ The same climatic conditions favored the evolution of the earliest ancestors of the human lineage Becoming Human What Makes a Hominin ● Major evolutionary novelties of humans ○ Habitual upright walking (bipedalism) ○ Characteristics of the dentition ○ Elaboration of material culture ○ Significant increase in brain size ○ Long developmental period and long lifespan ● Mosaic Evolution different traits evolve at different points in time Dentition ● 188.8.131.52 dental formula (same as in all Catarrhines) ● Y5 lower molar pattern ● Canine reduction ○ Canine size and shape is associated with behavioral differences in apes ○ Reduction of sexual dimorphism—>less malemale competition—>different social interactions ○ Canine3rd Premolar (CP3) honing complex of apes ■ Upper jaw has a gap by canine for lower canine called the diastema ■ The rubbing of the rubber and lower canine actually sharpens the upper canine ● Apes have Ushaped dental arcade while humans have a parabolic dental arcade ○ front part of ape dental arcade is wider, while course is more curved ○ this also characterizes the lower jaw ● Apes also have large canines, and broad incisors while humans have smaller teeth ● Chimpanzees have more facial prognathism ○ Humans have less facial prognathism and a smaller, shorter mandible Muscles of Mastication ● Temporalis action of closing the jaw ● Masseter originates on the cheekbones and inserts on the lower jaw, when this contracts they are responsible for the bite forces that can cut through foods ● Areas where these muscles attach are more robust and flaring on apes than they are on humans Anatomy of Bipedalism ● Not the only animals to do this but of the few animals to do this habitually ● Defining characteristic of humans ● Suspensory Locomotion and Vertical Climbing ○ Increased mobility of extremities ○ Shoulder blade located on back ○ Forelimbs elongated compared to hind limbs ○ Long and curved fingers for grasping branches ● Knuckle Walking ○ Wrist joints are stabilized ● African apes have long upper limbs 9inherited from an ancestor with suspensory locomotion) ● Dorsal positions of the shoulder blade ● Humans have inherited these adaptions as well ● Bipedal Locomotion What anatomical modifications are needed to become a habitual biped ○ Center of Gravity ■ Fixed point, through which body weight is transmitted or balanced ■ When humans stand, the COG is situated directly in the midline ■ Only minimal muscle activity is needed to maintain standing posture ○ Foramen magnum position ■ Foramen magnum is positioned directly underneath the skull in humans—pull through which your spinal cord passes ○ Body proportions ■ Intermembral Index = (forelimb / hindlimb) X 100% ■ Chimpanzee ~ 110% ■ Humans ~ 70% ○ Vertebral Column ■ Cervical (neck) and lumbar (lower back) curvatures to maintain center of gravity over the pelvis ■ Larger size of the lumbar vertebrae to support body weight ○ Pelvis Shape ■ Humans have a wider, basinshaped pelvis with short, broad, curved iliac blades ■ Apes is much longer and not as wide, less curved iliac blades, laterally flared ■ Iliac Blades repositions the gluteal muscles on humans creating improved lateral stability during swing phase of bipedal walking ■ abduction bringing your leg out to the side ■ repositioning of gluteal muscles allows for abduction in humans which is important because they allow for us to counteract instability of falling over when we are on one leg ■ method to lateral stabilize the pelvis so that we don’t fall over when we are on one leg when we are taking steps ○ Knee ■ Valgus angle of the knee ■ When humans walk, the foot falls directly below the center of gravity ■ Femur is oriented at an angle ○ Foot ■ Big toe is not opposed to the other four digits, and is enlarged in size ■ Enlarged heel (calcaneus) ■ Development of arches