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Week 5 of Notes, Bio Anth

by: Jaimee Kidd

Week 5 of Notes, Bio Anth Anth 1001

Jaimee Kidd
GPA 3.6

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Forces of Evolution and Formation of Species
Biological Anthropology
Shannon C. McFarlin
Class Notes
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This 7 page Class Notes was uploaded by Jaimee Kidd on Wednesday February 17, 2016. The Class Notes belongs to Anth 1001 at George Washington University taught by Shannon C. McFarlin in Spring 2016. Since its upload, it has received 21 views. For similar materials see Biological Anthropology in anthropology, evolution, sphr at George Washington University.

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Date Created: 02/17/16
Forces of Evolution Population • = A group of organisms potentially capable of successful reproduction ◦ Individuals of a population tend to choose mates from within the group ◦ The largest reproductive population is the species Genes in Populations • The population is the unit of evolution • Evolutionary change over time are not changes that occur during the lifetime of a  population, but within the phenotypic structure of these organisms and species overtime ◦ Result is the change of an appearance of the trait or genetic substructure of the  trait • Gene Pool= The sum of all alleles carried by the members of a population • Evolution= A change in allele frequencies from one generation to the next  • Genetic Equilibrium= no changes in the allele frequencies, i.e. no evolution is occurring in the population Hardy­Weinberg: Model of Genetic Equilibrium • Used to determine whether or not evolutionary forces areoperating on the population, for  a given genetic locus • Measure observed genotype frequencies for specific traits, and compare them against  predicted genotype frequencies assuming no evolution is occurring ◦ In other words, Hardy Weinberg provides a genetic model (or null hypothesis)  against which we can compare observed genotype frequencies in a population to  determine whether evolution is occurring at a given genetic locus • Two alleles: Dominant (A), Recessive (a) • Frequency of alleles: Dominant (p), Recessive (q) • p + q = 1 • To calculate expected proportions in a specific population we calculate the probability of  each possible genotype combination ◦ (Chances of A combining with A to form Genotype AA) p x p = p^2  ◦ (Chances of A combining with a or a combining with A to form Aa or aA) p x q + p x q = 2pq ◦ (Chances of a combining with a to form aa) q x q = q^2 ▪ p^2 + 2pq + q^2 = 1 • Assumptions made in this model ◦ Mating is random ◦ No new alleles are being introduced Forces of Evolution • Factors occurring in natural populations that cause changes in gene frequencies over  multiple generations ◦ (1) Mutation ◦ (2) Natural Selection ◦ (3) Genetic Drift ◦ (4) Gene Flow ◦ (5) nonrandom mating ▪ Hardy Weinberg assumes that these are not occurring • (1) Mutation ◦ An alteration in the genetic material ◦ Mutations are chance events ◦ rare events ◦ give rise to new alleles ◦ add variation to the gene pool ▪ most important thing because they are the only force that adds variation to  the gene pool • (2) Natural Selection ◦ Alleles that confer an increased likelihood of survival to reproduction will be  passed on to the next generation with greater frequency ◦ Different types of selection: ▪ Stabilizing: maintains a certain phenotype by selecting against deviations  from it (normal looking graph, up then down) ▪ Directional: selection fro greater or lesser frequency of a given trait (shift  in graph) ▪ Disruptive: maintains extreme values in the population (dip in the graph,  two humps) • (3) Genetic Drift ◦ = Change in gene frequency in a population over time, caused entirely by random  factors ◦ Assumes that we are taking information on a population that is infinitely large ◦ Sampling error effects: more likely to change the frequency of alleles in a  small population ▪ Population bottlenecks: severely reduces population is and genetic  diversity ▪ limits genetic variation ▪ losing variation ▪ Founder Effect: involves an element of geographic isolation such that the  new population becomes a variation of the parent generation  ▪ in humans this is seen with migration, groups  of people that migrate to a new area tend to be closely related so  that their genes are close to the same  • (4) Gene Flow ◦ = movement of individuals and their genes between populations ◦ Makes populations more similar to one another ◦ Counteracts the evolutionary forces that cause populations to diversity  • (5) Nonrandom Mating ◦ Inbreeding ▪ raises the frequency of homozygous genotypes at all loci ▪ decreases the frequency of heterozygous genotypes at all loci  ▪ also increases the likelihood that negative recessive alleles will build up ▪ ex. build up of hemophilia in royal families of England ◦ Assortative Mating ▪ Negative AM: increases frequency of heterozygous genotypes for  particular loci ▪ Positive AM: increases frequency of homozygous genotypes for particular loci  Formation of Species Microevolution vs Macroevolution • Microevolution: Small changes occurring within a species, such as changes in allele  frequencies. • Macroevolution: Large changes produced after many generations, such as the appearance  of new species. ◦ Micro and macro are part of the same continuum of evolutionary processes Definition of Species • Biological Species Concept ◦ Groups of inter­breeding natural populations, which are reproductively isolated  from other such groups. Ability to produce fertile offspring. 1 Reproductive isolation 1 Physical Barriers: ex. geographic 2 Intrinsic Barriers: ex. physiology, behavior 2 Reproductive Isolating Mechanisms 1 Pre­mating Mechanisms 1 Habitat Isolation 2 Temporal Isolation 3 Behavioral Isolation 4 Mechanical Incompatibility  2 Post­mating Mechanisms 1 Sperm­Egg Incompatibility 2 Inviability of Zygote­Fetus or Offspring 3 Offspring Sterility • Recognition Species Concept ◦ Emphasized unique traits or behaviors that allow individual members of the same  species to recognize each other for the purposes of mating  1 According to this, individuals from separate species should not recognize one  another as viable mating partners 2 Natural selection should favor those traits that are active in species recognition for mating • Ecological Species Concept ◦ A group of organisms exploiting a single ecological adaptation  1 Assumes that there is an adaptive gap separating ecological zones that allow  intermediate type of species from being successful 2 If the intermediates or hybrids are always going to be outcompeted over the  normal species, than the hybrid species frequency will not prevail  largely,especially since they are unable to exploit their resources and environment to best serve mating purposes • Evolutionary Species Concept ◦ Defines species as evolutionary lineages (ancestral descendant sequences of  populations) with their own unique identity  ◦ Has been criticized for its vagueness ◦ Oen criterion on which these species are rectified is based on phenotypical  identity, how similar they look, etc. ◦ Also important to keep in mind the time on a historical framework that the beings  exist to concur whether or not they are defined a species, as well as the space they take up, geographically speaking  1 Ultimately it is based on, do they live in a similar time span, in a  similar geographical location, do they look alike? • Morphological Species Concept ◦ Defines species based on anatomical similarities 1 Not very reliable because some species can be polymorphic and different species  can be very similar 2 But sometimes is the only one that can be used (paleontology) 3 Similar to Evolutionary Concept, except there is no concept of time and space Major Modes of Speciation • Two Modes of Speciation ◦ Anagenesis ▪ One species evolves into another over time, basically a line of species ▪ When one species becomes another, the previous species no longer exists 1 Difficulty: picking out the boundaries between different species ▪ Chronospecies­ each species within an anagenetic line  ◦ Cladogenesis ▪ One species splitting off into multiple species ▪ The first species can die out, but also can continue to live on ▪ More of a splitting kind of evolution • Processes of Speciation ◦ Allopatric Speciation ▪ Speciation occurring via complete geographic isolation ▪ Some kind of physical barrier appears, such as a river, this serves to  separate one or more segments of a population off from the parent  population 1 Thus, these segments experience a slightly different environment and  speciation occurs ▪ No more gene flow between the isolate and parent population allowing for isolate populations to continue to diverge further  ◦ Parapatric Speciation ▪ Speciation involving only partial geographic isolation  ▪ Divergence­ 1 Natural Selection, combines with partial geographic overlap to create a new  species, so there is still some gene flow although it still allows for variations  from natural selection 1 differential natural selection on the outer most isolated areas, which  further pulls apart species  2 Prevents complete speciation of individuals, however, the two different  remote ends of the populations look very different but where their  geographic range overlaps the species look more similar than not (this area is the hybrid zone, capable of interbreeding) 1 ex. Baboons  ◦ Sympatric Speciation ▪ Speciation occurring in the absence of geographic isolation ▪ Very strong section favoring different phenotypes can create speciation  affects ▪ Requires one population diverging from another population in the same  environment ▪ Can also occur in an area with limited resources, where different aspects  to use resources help select the survival of certain species  ▪ Could happen through chromosomal mutations  Patterns of Adaptive Change • A niche is how a species “makes a living,” which includes how it interacts with its  environment, with other species in its community, and how it utilizes resources in its  habitat ◦ each species has a unique role in their environment  • Species that live together in the same habitat must have different niches in order to avoid  being in direct competition with other species—no two species can occupy the  same niche, or one would outcompete the other inevitably  • Adaptive Radiation ◦ When a single kind of organism diversifies to fill many available niches. Tends to follow the origin of an evolutionary novelty.  ▪ Each species has some sort of variation of that novelty and can exploit the  environment in a new way  ▪ Allows them to diversify  Tempo of Speciation • Gradualism ◦ Evolutionary change proceeds gradually through accumulated small­ scale changes • Punctuated Equilibrium ◦ Evolutionary change proceeds through long periods of stasis and rapid periods of  change  ▪ long periods of stasis punctuated by rapid change during speciation  Principles of Classification • Systematics = the study of the diversity of life and the relationships at all levels in the  hierarchy ◦ Kingdom­ animals ▪ Phylum­ possess a nerve cord (major body plans) ▪ Class­ warm­blooded with mammary glands ▪ Order ▪ , Family, Genus, Species • Taxon = a group of organisms assigned to a particular level in the classification  • Species: basic unit of biological classification ◦ Binomen: Homo sapiens ▪ Genus name is Homo ▪ Species name is sapiens  • What Criteria Do We Use? ◦ Similarities are a good starting point. ▪ Similarities must reflect descendant from a common  evolutionary ancestor  ▪ Some similarities arise for other reasons, so not all similarities are equally  informative  ◦ Analogy ▪ Structures that are similar among organisms in properties (e.g. superficial  appearance and function) but evolved independently and are inherited  from different precursors ▪ These are similarities in function, not in common ancestry ▪ Separate adaptations that have evolved independently ▪ Homoplasy ▪ ex. wings, bats and birds are not related although they both  evolved wings ◦ Homology ▪ Similarities that are shared between organisms because they were  inherited from the same structures in a common ancestor ▪ We avoid analogous traits, and use homology to reconstruct evolutionary  relationships  ▪ Derived vs. Ancestral Homology ▪ Not all homologies are equally informative for reconstructing  evolutionary relationships ▪ Ancestral Homology: symplesiomorphy, shared with the  other descendants of common ancestry, such as all primates having mammary glands, or presence of hair, these traits do not distinguish them as primates, but is shared with their  common ancestors of mammals ▪ Derived Homology: synapomorphy, used to define clades  (groups with a common ancestor), distinguished group  from other common ancestors, uniquely evolved, traits that  are not present in other common ancestors and are telling of their species, newly evolved features that provide their  evolutionary distinctiveness ▪ Reconstructing Phylogeny ▪ phylogenic trees are built using large sets of traits (for extant and  recent fossil species, DNA sequences can be used)  ▪ shows degrees of relationships between related groups of taxa ▪ Cladogram: if we add geological time, we get a phylogeny 


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