Week 4 ANTH 1001
Popular in Introduction To Biological Anthropology
Laura Castro Lindarte
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Popular in Biology/Anthropology
This 7 page Class Notes was uploaded by Laura Castro Lindarte on Saturday September 24, 2016. The Class Notes belongs to ANTH 1001 at George Washington University taught by W. Andrew Barr in Fall 2016. Since its upload, it has received 9 views. For similar materials see Introduction To Biological Anthropology in Biology/Anthropology at George Washington University.
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Date Created: 09/24/16
September 12, 2016 The Forces of Evolution ● Population: group of organisms potentiall apable of successfully reproducing ○ Individuals tend to choose mates from within group ○ Evolution occurs to a population, not individuals ○ The largest reproductive population is species, population can range from small group to whole species ● POPULATION IS UNIT OF EVOLUTION ○ Individuals can change but not all changes will get passed down so not evolution ● Gene pool: sum of all alleles arried by members of population ○ Can look at allele frequency (how many of each alleles seen) and genotype frequency (how many have specific combination of alleles) ○ Number of both frequencies can be different ● Evolution: change in ALLELE FREQUENCY in population from one generation to the next ○ When allele frequency change then evolution has occurred, i f frequency if NOT changing then it is in GENETIC EQUILIBRIUM (no evolution is occurring) ● HardyWeinberg: model of genetic equilibrium ○ Null model: looking to see i volution is occurring to a specific allele ets up frequencies when no evolution is occurring to compare observed frequencies to see if evolution is seen ○ Ex: dominant = A, recessive = a; frequency of dominant = p, frequency of recessive = q so p + q = 1 ■ Only 2 alleles ■ Number of alleles always double of number of individuals because all have two ○ Chances of AA → p x p = p2 ○ Chances of Aa or aA → p x q p x q ○ Chances of aa → q x q = q2 so… 2 2 p + 2pq + q = 1 (HardyWeinberg equation) ○ Assumes that mating is random, population are infinitely large → i f frequencies don’t go with equation then evolution occurs ○ Ex: p = heads (H) so 50%, q = tails (T) so 50% so… HH p x p = p 0.5 x 0.5 = 0.25 HT p x q 0.5 x 0.5 = 0.25 TH p x q 0.5 x 0.5 = 0.25 2 TT q x q = q 0.5 x 0.5 = 0.25 0.25 + 0.5 + 0.25 = 1 ○ Ex: population: 100 cats; traits : fur pigmentation; phenotype: black, orange, calico; genotype: BB, OO, BO (codominance) 1. Calculate observed genotype f requency 2. Calculate observed allele f requency 3. Use the HW formula to calculate xpected genotype frequencies under conditions of NO EVOLUTION: p + 2pq + q = 1 2 2 BB → p = 0.45 = 0.2025 BO → 2pq = 2(0.45)(0.45) = 0 .4950 2 2 OO → q = 0.55 = 0.3025 4. Compare calculated frequencies to actual frequencies: a. Since not same number and statistically significant difference then evolution is occurring and not favoring calico b. Then would be interested in what is causing evolution ● Forces of evolution: f actors occurring in natural population that c ause changes in gene frequency over multiple generation 1. Mutation 2. Natural selection 3. Genetic shift 4. Gene flow 5. Nonrandom mating ● Mutation: ○ Alternation of genetic material (RANDOM) ○ Rare and give rise to new alleles: dd new alleles that didn’t exist before ○ INCREASES VARIATION ● Natural Selection: ○ Alleles that allow organism to reach reproduction age will be passed down NOT RANDOM, based on survival) ○ This is where environmental changes come into play ○ Acts on phenotype and reflected in genotype 1. Stabilizing: aintains by a certain phenotype by electing against deviations from it (acts on extremes) a. Ex: birth weight in human infants, underweight and overweight infants are more likely to die so middle weight infants are favored 2. Directional: election for greater or lesser frequency of given tr ne of the extremes is more popular a. Seen in Darwin’s finches changing beaks due to droughts 3. Disruptive: both extreme favorable but middle not (less common) ○ DECREASES VARIATION ● Genetic drift: change in gene frequency over tim ue by random factors ○ No natural selection or mutation, just luck ○ Sampling error effects: more likely to change mall population ○ Population bottleneck vents that make only a few survive so only their alleles survive ■ Event is dramatic and not give time to have non random natural selection ■ Ex: Cheetahs are very similar genetically because bottleneck only allowed few to survive ■ Humans are much more related too ○ Founder effect: individual leave and only their traits seen in population in new area ● Gene flow: movement of individuals and genes etween population ○ Make populations ore similar to one another ○ Counteracts the evolutionary forces that causes populations to diversify ● Nonrandom mating: ○ Inbreeding: increases frequency of homozygous of particular loci, decreases heterozygous of particular loci ○ Assortative mating: ■ Negative: increases frequency of heterozygous genotypes of particular loci, looking for similar individuals to you to mate ■ Positive: increases frequency of homozygous genotypes of particular loci, looking for different individuals to you to mate September 21, 2016 Formation of Species ● Microevolution: mall changes occurring ithin a specie uch as changes in allele frequencies ● Macroevolution: larger changes produced fter many generations uch as appearance of new species ○ Microevolution can lead to macroevolution if given enough time (accumulation) ○ Same processes but different scale ○ Darwin focused on micro ● Big question in human origins i ow many species are there? ● Species concept debate: not one agreement on how to define what a species is and what is best mechanism for knowing if two populations are same/different species ○ Most commonly known is b iological species concept (BSC roups of interbreeding natural population which a eproductively isolat rom other groups ■ Can and will they reproduce in the wild. ○ Reproductive isolation: ■ Not only how they look but how they act ■ Physical barrier geographic) ■ Intrinsic barri physiology, behaviour) a. Ex: appearance or courtship rituals ○ Reproductive isolating mechanisms: ■ Premating mechanisms: p rior to process a. Habitat isolation: l ive in different habitat in same ecosystem so don’t come into physical contact b. Temporal isolation: aving different mating season c. Behavioral isolation: eproductive behaviour is different d. Mechanical incompatibility: i ncompatibility of mating structures ■ Postmating mechanisms: after physically mating a. Spermegg incompatibility: emale body might attack sperm from other species or sperm can’t penetrate egg b. Inviability of Zygotefetus: i nstantaneous abortion of fetus c. Offspring sterility: offspring not able to reproduce (ex: mule) ○ All in natural world, in captivity some might mate (ex: liger) ■ Female liger is fertile while male is not ■ Also zeedonk, wholphin ○ BSC can be hard to apply to some things like hybrids, two species not being together over (location or fossil) so can’t be tested ● Differences between species ccumulate through time ○ At first there are small differences so hard to tell species apart when recently split ● Recognition species concept: UNIQUE TRAITS that allow members to recognize each other (do they recognize others as member of species?) ● Ecological species concept: group of organism xploiting a SINGLE ECOLOGICAL ADAPTATIONS (hybrids won’t be as fit) ○ Adaptive gap between species that make unfit ○ Species are in optimal fit zone for their environment, natural selection important ● Evolutionary species concepts: defines volutionary lineages with their own unique identity (is ancestraldescendant sequence unique to species?) ○ Hard to apply because might have gaps in fossil record ● Morphological species concept: looks NATOMICAL SIMILARITIES, p roblem because species can be olymorphic (have different traits) ○ Sometimes it is the ONLY one you can use because only have anatomical data ■ Paleontology ● Major modes of speciation: how came to be? ○ Anagenesis: evolutionary change occurring i ne evolutionary lin ifference occurring within one species (NO SPLITTING) ■ Chronospecies: specific species within an anagenetic line ○ Cladogenesis: one species PLIT to create different daughter species ○ Can both happen to one ancestor tree ○ Different processes of cladogenesis: ■ Allopatric: because of OMPLETE geographic isolation a. Ex: fruit flies separated in lab b. Most common c. Divergence will occur often when population separated due to mutation, genetic drift and natural selection ■ Parapatric: because of ARTIAL geographic isolation a. Ex: hamadryas baboon and anubis baboon being different species but having big hybrid zone because still live close to each other b. Divergence will occur often when population separated due to mutation, genetic drift, nonrandom mating and decreased gene flow ■ Sympatric: because of ABSENCE g eographic isolation a. No isolation b. Divergence will occur often when population separated due to mutation, natural selection, mate recognition and selective breeding ● Niche: how species makes its living ○ Species that live together need to have NICHE DIFFERENTIATION to avoid direct competition (ex: primates different due to the different levels of the rainforest that they live in) ● Adaptive radiation: single kind of organism d iversifies to fill many different niches ○ Tends to follow the origin of an evolutionary novelty ● Tempo of speciation can be: ○ Gradualism: accumulated small changes ○ Punctuated equilibrium: s taple for a LONG time then smart period of a lot of change