Anthro 5 All Lecture Notes.docx

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Anthro 5 – Intro to Physical Anthropology 9/22/2011 10:50:00 AM I. Class Logistics a. Class website: i. Syllabus, lectures, announcements, assignments, links b. remember to register i-clicker online (gauchospace) c. homework i. ideally read chapters ahead ii. problem sets graded fairly easily II. The Central Problem of Biology a. Adaptation: why are organisms so well adjusted to their circumstances? i. Camouflage: animals eat other animals; camouflage is used to protect and blend b. life is: i. organized, complex, adjusted to its circumstances, reproduced ii. why is life all of these things? 1. the process that creates it; evolution by natural selection: Darwin and Wallace published 1858 a. borrowed 1-3 of 6 step argument from Thomas Malthus; founder of demography: study of populations b. step 1: reproduction is exponential (rapidly increases over time) i. not 2, 4, 6, 8, 10 but 2, 4, 8, 16, 32 ii. ex: elephants; begin to reproduce at 30; have 1 offspring per decade until age of 90; therefore each pair has 6 offspring  9,000,000 per pair after 750 years c. step 2: numbers of organisms tend to be relatively stable in nature d. step 3: many individuals must fail to reproduce e. step 4: individuals with advantageous traits are more likely to survive and reproduce (natural selection) f. step 5: offspring resemble their parents i. successful parents pass on advantageous traits; unsuccessful parents don’t pass on traits g. step 6: advantageous traits become more common over the generations i. ex: bill shape in Darwin’s finches; climate affects composition of “seed bank”  different shaped bills better suited to seed bank become passed down traits in Galapagos finches  climate shifts ultimately changed bill shape 2. natural selection is the unremitting engine of biological design: EXPLAINS WHY a. life is organized, complex, adapted to its circumstances, and able to reproduce b. our own species (and all others) has unique configurations of traits it does 3. limits to kinds of advantageous traits selection can spread? a. Yes; traits must be transmitted from parent to offspring, or genetically b. Trait must justify its cause vs. cost  cause for the trait in an organism must be of greater worth than the cost 4. natural selection builds a. adaptations b. selects the most effective genetics variants in each generation Anthro 5 – Intro to Physical Anthropology 9/22/2011 10:50:00 AM I. evolution by natural selection a. reproduction has the potential to be exponential b. almost never is exponential in the real world c. only way it could fall short of exponential is if individuals fail to achieve reproductive potential d. reproductive success is nonrandom with respect to traits e. offspring resemble their parents f. traits that foster reproductive success will accumulate in the population g. NATURAL SELECTION: differential reproduction of heritable traits because of a better fit with the environment II. what determines whether a trait is advantageous? a. The environment; nature b. Natural selections sorts available alternatives in population and holds whatever traits work c. Advantageous trait: any trait that promotes reproduction i. “survival of the fittest”; survival is a means to an end, not an end in itself 1. ex: A wants to live as long as possible, but B wants to live to but will compromise life to promote offspring  evolution occurs and A will all be dead while there will be descendants of B  III. designing organisms a. natural selection designs organisms  therefore designs them for goal of reproduction b. adaptations: traits that have been preserved by selection because they aided reproduction i. why past tense? 1. These traits obviously aided organisms in the past, but we’re still waiting to find out if they meet challenges (aid organisms) of the present and future ii. many kinds of creatures due to different environments a. traits that work in one environment may fail in other environments b. ex: whale (water animal) versus caribou (land animal) iii. selection IS NOT an engineer, but IS a tinkerer a. tinkerer: a person skilled in various modes of mechanical work b. selection can’t create new alternatives; only chooses among available alternatives (mutation) iv. homology: the way evolution recycles old elements to convert them to new elements (ex: forelimb of frogs, birds, cats, and humans are all very similar) a. peel back muscle and skin of whale flipper  find an arm v. *NOTE* natural selection best described as: the selective retention of specific alternatives in a population vi. precision of adaptation a. how can selection (differential reproduction) achieve such perfection? b. My parents reproduced, their parents reproduced, ancestry continues back and back  we’re inevitably the descendants of the “winners” since the beginning of time vii. any limits to kinds of advantageous traits selection can spread? a. Every trait has associated costs; trait must produce net positive reproductive effects (benefit > cost), otherwise selection won’t favor it b. A trait must be transmitted reliably form parent to offspring; otherwise selection won’t spread it (e.g. genetically based traits)  IV. science starts with observations b. Mendel’s results: bred pure strains of wrinkled and round together c. F1: Wrinkled x round; offspring were all round; hence, no blending d. F2: takes round offspring  round x round o ¾ round: ¼ wrinkled  d. science checks to see if results are  replicable; Mendel regularly got the same  results 1. Mendel’s model a. Particles, not fluids (genes) b. Adults have a double dose of particles (diploid adults) c. Adults give only half of their double dose to each offspring (haploid gametes) d. Some particles have stronger effects than others (dominance)  F1 hybrid (round) x pure wrinkled (do it yourself) o Ss x ss  50% wrinkled, 50% round  Genotype: the genes themselves (smooth vs. wrinkly)  Phenotype: the outward expression of those genes  Allele: variant of a gene, for example: wrinkled allele and round allele of the seed-shape gene; alternative versions of the same gene  Homozygous: two matching alleles (SS and ss)  Heterozygous: two different alleles  Recessive allele: expressed only when homozygous  Dominant allele: expressed even when heterozygous  Two parents are homozygous for different versions of a trait (AA and aa). Assuming the trait exhibits complete dominance, their offspring:  All display the dominant phenotype  Have a mix of phenotypes 3 dominant for every 1 recessive  Have a mix of genotypes: approximately 3 recessive for every 1 dominant  All homozygous  Will be half homozygotes and half heterozygotes  Chromosome: linear aggregation of genes (mostly in nucleus)  Locus (plural  loci): place on a chromosome where genes for a particular trait occur  genes are alleles of each other if they can occur at the same locus  diploidy: each chromosome is paired, with one from mom and one from dad  loci match, but alleles may not (if heterozygous)  sex cells (gametes) could be formed by simply giving either your paternal or maternal chromosome to each gamete  gamete formation involves recombination (crossing over)  exchange of genetic material between maternal and paternal chromosomes  result = increased genotypic diversity; each chromosome has part maternal matter and part paternal matter; the other chromosome of the diploid is the compliment of the first chromosome (matching)  first chromosome 75% mom 25% dad; second chromosome 75% dad 25% mom Anthro 5 – Molecular Genetics 9/22/2011 10:50:00 AM  Goals  Understand structure of genes  Understand how this structure allows them to make precise copies  Understand how this structure allows them to shape phenotypes  Gene structure has three elements  Phosphates (invariant)  Sugars (invariant)  Bases (variable)  Base pairing rules follow from different types of electron bonds  Always has phosphate, sugar, base *on both sides*  A  T (double bond)  C  G (triple bond)  DNA will always be able to make perfect copies of itself o Zip down the middle; knows what’s missing/what needs to be made based on the A/T/C/G patterns  Therefore, base pairing rules allow perfect DNA replication o When reproduce, body doesn’t give YOUR genes to offspring, but gives REPLICAS of your genes made by base pairing rules  Humans are diploid; this means that:  In the DNA, for every sugar molecule, there is a linked phosphate molecule  For every base in the DNA structure, there is a matching pair (A/T and C/G)  For every trio of bases on the mRNA, there is a complementary trio on the tRNA  In each cell, there is one of each chromosome  For each chromosome, we receive a copy from our mother and a copy from our father  The same kinds of rules allow DNA to serve as a template for phenotypic instructions; called gene expression  gene expression: how genes specify the recipes for proteins  tRNA: transfer RNA  mRNA: messenger RNA o RNA vs. DNA  RNA is single stranded  DNA is double stranded  Both use 4 bases, but 1 base is different; DNA uses T while RNA uses U  Ribosome: searches for three successive bases on RNA strands (if one side has AGG, ribosome looks for UCC to match) o Each triplet of three bases represents an amino acid  Genetic and phenotypic variation: point mutations  DNA sequence variation in a gene can change the protein produced by the genetic code  Tying back to evolution: better, more successful genetic strands get passed on to offspring  Prerequisites for natural selection  1. Heritable 2. Variation that is 3. Associated with differential reproduction  mutations provide supply of new heritable variation  some variants work better than others and get passed to more offspring  QUESTION: Why might a particular point mutation be “invisible” to natural selection?  Selection rejects all mutations because they are copying errors  Point mutations only affect ribosomes  Some codons code for more than one amino acid  Some amino acids can be specified by several different codons  None of the above  QUESTION: mutations  Are errors in gene copying  Provide the raw material for evolution  Create new alleles  Are sometimes “invisible” to selection  All of the above o Mutations are random with respect to the direction of adaptation o Mutations create competing evolutionary units o Thus, evolution by natural selection is a two-step process  Production (by mutation) of random alternatives (alleles, and the proteins they specify); sickle cell example  The highly non-random sorting of these alternatives by natural selection  What is selection’s criterion? o The ability of the allele to get into the next generation Genotype – Environment Relationships 9/22/2011 10:50:00 AM  Gene action  Useful to recognize two types of gene action o Obligate: resist environmental interference  Difficult to find  Obligate variation can be either o Discrete: just two or a few values  ex: height of Mendel’s peas o Continuous: many values with no obvious gaps in the distribution  Ex: height in humans o Facultative: monitor environmental variation and adjust phenotype accordingly  Touch-stone example: sun tanning o Your genes don’t change when you suntan, but your phenotype does o Changes by rules coded for in the genes o How does sun tanning work?  Rate of melanin synthesis (which is a protein) increased with more UVb exposure  UVb has multiple effects on the body o + necessary for synthesis of vitamin D o - causes skin cancer  too little UVb = vitamin D deficiency  too much = skin cancer o What do we do to get the right about?  Block UVb when there’s too much and let more in when there’s less  Melanin is a narrow-range, specific UVb blocker  Produce more or less melanin depending on which risk is greater = sun tanning  Relative risks vary with latitude, so populations at different latitudes differ in baseline (natal) rates of melanin synthesis o UVb also varies with the season, so relative risks (cancer and vitamin D decifiency) are not constant  Therefore, facultative adjustment is needed o QUESTION: a sun tanning adaptation  Depends on seasonal genetic changes  Involves a link between melanin synthesis and exposure to sunlight  Has been designed by selection because relative risks change over an annual cycle  Involves a phenotypic response to an environmental variable  All of the above are true except A  Facultative adaptations are genetically programmed response patterns built by selection o Like all adaptations they serve reproductive success o Nature wrote the rules for how nurture works  Facultative adaptations versus susceptibilities: o Sun tanning versus sun burning  Spending all winter inside, then going on spring break  very low UVb exposure to very high UVb exposure quickly  Turn the thermostat up 10 degrees in a crowded lecture hall  various responses: sweating, take off sweater, etc.; turn the thermostat up 100 degrees  leads to changes in phenotypes o Programmed response versus a failure to respond o Sweating versus spontaneous combustion o Facultative traits operate over historical range of variation  Another example: mate guarding in soapberry bugs o Males engage in mate guarding: after reproducing with female, they leave reproductive organ inside her  Benefit: other males can’t inseminate “your” female; male aiming to fertilize as many eggs as possible  staying inside = less competition between other males  Cost: there are other females out there, so if the male is attached to one female, he can’t inseminate other female bugs  Facultative adaptations are genetically programmed response patterns built by selection o Track the environment o Some facultative traits are irreversible o Some depend on internal environments o Some depend on sex (male/female)  QUESTION: Pick the true phrase. o Obligate traits are always discrete o High levels of mate guarding would always be adaptive o Sun tanning is not an adaptation o Selection generally favors obligate traits o None of the above  Nature versus Nurture  nature o in the genes o innate o instinctive o fixed and inflexible  nurture o from experience o learned o environmental o flexible  two questions: o What causes sexual orientation?  This issue is development  What combination of genes, fetal environments, nutrition, peer experiences… led to the phenotype we see?  These interactions may be preprogrammed (ex: sun tanning)  Just focused on one individual o What explains individual differences in sexual orientation?  Question about why there is variation in a population  People differ in both the genes they carry and in the environments they have experienced  A group of individuals in population  why aren’t we all the same?  Vp is the phenotypic variation in a trait  “variance” in the statistical measure of variation  we can “partition the variance” o How much of the phenotypic difference between individuals:  is associated with the fact that they have different genes?  And how much is associated with the fact they have different experiences?  Phenotypic variance (Vp) has two components: Vg and Ve o Vg is the fraction of phenotypic variance that is associated with individuals having different genes affecting the trait o Ve is the fraction of phenotypic variance that is associated with individuals having different experiences affecting the traits o Vp = Vg + Ve  Phenotypic variation is the sum of: o Underlying genetic variation o + o the effects of different environments on the expression of those genes  Heritability: (h^2) the proportion of total phenotypic variance that is due to the fact that individuals have different genes o h^2 = Vg/Vp o therefore: o h^2 = Vg/(Vg+Ve) o h^2 varies from 0 to 1 o what kinds of traits have low (or high) heritability?  Low  what if Vg were zero? o No genetic variation; very common because selection gets rid of the unfavorable alleles  ay trait where we’re all homozygous for the same gene  Ex: we all have two eyes; in humans there seems to be no genetic variation associated with the number of eyes (eye number has heritability of 0)  Low  what if Ve were large? o Ex: what language you speak o All phenotypic variance seems to be environmental o No genes for mandarin vs. Spanish  Speak a language based on how you’re raised at home  High  what is vg were large (compared to Ve)? o Ex: blood type o No Ve; all Vp is the consequence of Vg o Hence h^2 = 1 o Selection is more effective when heritability is significantly greater than 0  Selection evaluates phenotypes: some reproduce at higher rates than others  passing on the genes that built those better phenotypes  as long as there are genetic differences between better and worse phenotypes  As long as heritability > 0 o Selection is more effective when heritability is significant  What happens as selection operates?  it reduces genetic variance  therefore reduces heritability  “selection uses up heritability” (new mutations can reprovision it)  Summary  Mutation can be obligate (discrete or continuous) or facultative  An individual’s phenotype is the result of thousands of gene- environment interactions  But the phenotypic variation in any population of individuals can be divided into a fraction that is associated with due to genetic differences and a fraction that is associated with environment differences  QUESTION: Which of these is correct?  All genes are made out of RNA  All genes have fixed and invariant effects on the phenotype  Genes tend to mutate in the direction of higher fitness  Eye color has high heritability  None of the above is true Homosexuality and Heritability 9/22/2011 10:50:00 AM  Why hasn’t selection eliminated male homosexuality? (What explains the variation in sexual orientation?)  Incidence (frequency)? o At least 2% of men and 1% of women o Too frequent to be due to mutation o Selection must have increased the frequency of the relevant genes  Purely environmental, not caused by genes? o No, significantly heritable ~ 0.5  The h^2 of male sexual orientation is approximately 0.5  What does that mean? o Nothing about development o Nothing about what causes an individual’s sexual orientation o Half the variability in sexual orientation in the population is due to the fact that individuals have different genes  How do we know the heritability is about 0.5? o Twin studies: o How likely is that the twin of a homosexual is also homosexual? o Does that differ depending on whether the twins are monozygotic (genetically identical) or dizygotic?  Purely environmental, not caused by genes? NO  significantly heritable ~0.5  Does not reduce fitness? Yes, it does. (gay men have 1/10 the reproduction abilities of straight men)  Favored by kin selection? No, gay men do not systematically aid kin (more than straight men)  Sexually antagonistic genes? Research suggests that a gene on the X-chromosome is associated with homosexuality o What is a sexually antagonistic gene?  A gene with opposite fitness effects in the two sexes  Autosomal, or sex linked? Lower barrier to x-linked sexually antagonistic genes  Dean Hamer’s research  Pedigree studies: how is gayness distributed in families? o Can look at pedigree studies to see significant heritability of homosexuality through carrier women, etc.  Concordant brother studies: what genes do gay brothers share?  Suggests a gene on the X-chromosome that predisposes male homosexuality  Camperio-ciani et. Al.  Is there any evidence for a sexually antagonistic X-chromosome gene?  How would you look for it? What patterns would you expect to see? o In male relatives?  More gay men among matrilateral relatives o In female relatives?  Higher fitness among female matrilateral relatives (fitness = reproductive success) o Straight men won’t show either of these patterns ^  Why is it interesting that the relevant gene is on the X- chromosome? o Mutations could cause any phenotypic effect… but will selection favor them?  For a sexually antagonistic gene, the benefits in sex 1 must outweigh the costs in sex 2  But an X-chromosome gene must raise female fitness only half as much as it lowers male fitness in order to produce a net benefit  Environmental effects? Heritability = 0.5, so environmentality = 0.5  “older brother effect”  men with more older brothers are more likely to be gay; not older sisters; not older step-brothers, not older half-brothers related only through the father  only older male siblings who shared the same uterus (not a socialization effect) 33% increase  how might such a “uterine effect” operate? o Y-chromosome o They produce proteins (from genes coded on his Y) that are foreign to his mother’s body o She will produce antibodies (immune system defenses) against these y-derived proteins o More sons = more anti-y antibodies o These maternally produced anti-y antibodies might interfere with the y-derived proteins of her subsequent sons during their fetal development o This maternal interference could disrupt the male-typical traits that the fetus’ y-derived proteins are trying to produce  SUMMARY: At least two factors (one genetic and one environmental) contribute to phenotypic variation in male sexual orientation  A gene on the X-chromosome (Xq28) 14%  A uterine influence of older brothers 8%  These two factors only explain about 22% of the variance  78% of variance still unexplained  QUESTION: What is true about male homosexuality?  It has significant heritability  It can be explained by mutation alone  Homosexuals have normal levels of reproductive success  There are no known genes associated with it  None of the above  QUESTION: there is evidence that male homosexuality:  is purely environmental  is associated with a gene or genes on the x-chromosome  may produce fitness benefits in females  b and c are both correct  none of the above is correct  facultative effect: susceptibility Microevolution and Macroevolution 9/22/2011 10:50:00 AM  QUESTION: selection   Causes changes in allele frequency  Produces favorable new mutations  Always favors what is good for the species  Will be efficient when heritability is low  None of the above  Microevolution: generation by generation changes in gene frequency; happens in ecological time (time we live by)  Macroevolution: large scale changes in species over geological time (hundreds and hundreds of years)  NOTE: macroevolution is caused by generations and generations of microevolution  Uniformitarianism: the processes that shape the world are always the same (ex: gravity) o Scientific theories are uniformitarian o Hence, microevolution causes macroevolution o NOT the idea that the world is always the same  Gradualism: the idea that the changes that are incorporated over evolutionary time are small changes o Mutations of small effect are more likely to be helpful than mutations of large effect o Why?  microscope analogy o NOT the idea that evolution is always slow o Two implications of gradualism:  The formation of complex adaptations o Ex: the eye o Selection has no foresight o No allele will spread unless it confers an advantage in the present o So, complex adaptations must be built of small changes, each of which is beneficial  The formation of new species  How quickly can new adaptations arise? o That depends on the generation time, the amount of variation and the strength of selection o Lizard “seeding” experiment (in textbook?)  Take lizards from one island, and experimentally move them to another island (introduce lizard to new environment/habitat)  in new environment lizards forced to shift diet  Microevolution = change in allele frequency  Macroevolution? What happens overs millions of years?  New species arise (and others go extinct)  Can microevolution explain macroevolution?  Speciation: where do new species come from?  What is a species?  Defined by reproductive isolation  Members of different species don’t share enough genes (gene map); they can’t interbreed  All organisms are connected in an unbroken ancestor-descendant chain, back to the first gene-based life forms  How is that the various descendants become reproductively isolated?  All living chimps and all living humans share an ancestor  why can’t we breed with chimps?  This is the same as the question: where do new species come from? o A question about the origins of reproductive isolation o The simplest explanation is called the allopatric model o Oval with plots within it; range divided by a physical barrier  Individuals from west can’t breed with individuals from east  If environment changes and barrier disappears  two types might have evolved to be too different to interbreed (reproductive isolation) o Any factor that discourages gene flow can serve in place of the physical barrier  Ex: ecological separation within the same geographic range o QUESTION: pick the true statement  Gradualism implies that macroevolution is always slow  The allopatric model is a uniformitarian model of speciation  New adaptations (like the eye) generally arise from one big mutation  None of the above  Two lines of evidence suggest that the accumulation of small change can add up to a species-level difference  Domestic breeds (dogs  derives from wolves)  Ring species o Are ring species a problem for our gradualist theory of evolution by natural selection? o If lineages diverge gradually should it be the case that, at every moment in evolutionary time, some populations are “right on the cusp” of speciation? YES  If we couldn’t find such situations it would be an embarrassment for our theory  SUMMARY  Mutations (copying errors) create new alleles  These alleles compete with each other  Most mutations are harmful but those with the smallest phenotypic effects have the best change of being beneficial  Over evolutionary time selection spreads the most beneficial alleles  This process results in both: o Complex adaptations such as the eye o New species  TRUE OR FALSE?  There is evidence that many small-scale (microevolutionary) changes can add up to a species-level difference  True  False Classification and Phylogeny 9/22/2011 10:50:00 AM  Principle: classification should reflect phylogeny  Classification: clustering organisms in natural groups o Ex: sharks, oaks, birds, penguins o Not only do we have these categories, but we have a hierarchical arrangement  Vertebrates: mammals  primates (lemurs, monkeys, apes), bats, cetaceans; birds  swifts, ducks, penguins  Phylogeny: deducing ancestor-descendant relationships  This is what makes the groups “natural” o But what are the natural groupings?  They could be inferred from overall similarity? o Problems with that? o What causes similarity between organisms?  Shared ancestry  Convergence  makes distantly related forms similar (ex: sharks, whales, salmon) o Is a whale a fish?  No, but what makes you so sure? o Fin structure built differently o Nurse their young  Why are those traits important in deciding? o What are the natural groupings?  The ones created by evolution, of course  Those that share a common ancestor o But all life shares a common ancestor… o QUESTION: the fact that all organisms use DNA (or RNA) as their hereditary material is evidence that they are all related:  True  False  Explanation: in principle, every kind of creature could use a different molecule to transmit hereditary information  Cladistic classification is based on order speciation  Naturally produces hierarchical groups  Primitive versus derived similarities  Primitive: trait present in the common ancestor of the group  Derived: trait evolved since divergence from the common ancestor  QUESTION: Having two eyes is primitive for mammals:  True  False  Primitive versus derived similarities  Pentadactyly (having 5 digits) is primitive for mammals  It should not be used to find natural groups of mammals o But having one toe is derived for mammals o So those that have one toe may represent a natural group  How to decide what is primitive and what is derived?  Three methods: o Fossil record o Out-group comparison o Order of appearance in development  Cladistics principle: trait present in the outgroup is primitive  QUESTION: Which is the outgroup?  Humans  Nwm  Owm  Howler monkeys  Lemur  Process can be repeated for other traits (whether phenotypic or genetic)  Not all traits give same answer, but each trait counts as vote for one grouping arrangement or another  Arrangement that gets the most votes wins: maximum parsimony  QUESTION: what kinds of traits would be least affected by convergence?  Anatomy  Physiology  Behavior  DNA sequences  All equally affected Studying Adaptations 9/22/2011 10:50:00 AM  Natural selection builds:  Traits that meet the challenges of the environment (adaptation)  By selecting the most effective genetic variants in each generation  QUESTION: adaptations:  Are built from mistakes  Cause an organism to be well adapted to its current environment  Always benefit the survival of the species  Can be convergent in distantly related species  A and d are correct  Studying adaptations  what does this adaptation do? o Two methods:  Reverse engineering o Look at something that already exists, wonder how constructed o What features would the trait have to have, and how would they have to be connected?  Ex: bat sonar  High frequency, sampling rate, “send- receive” technology, exploit Doppler effect, anti jamming features o Look at the features, how does it operate?  Planned comparisons o “the comparative method” o what organisms are most likely to share traits?  Close relatives  True for individuals, and true for species  You and your parent vs. you and me  Chimps and humans vs. squid and humans o When closely related forms are similar, this is NOT news  Doesn’t show much evolution  Not much adaptive change shown o What if closely related forms DID differ; this IS news (divergence) o And if distantly related forms are similar is also news (convergence) o Both situations indicate adaptive evolutionary change o Example: eyes  Divergence: among closely related species of fish, some species lack eyes o Selection pressure absent when there is no light o prediction: cave dwelling species lack eyes  Convergence: among distantly related species of fish, shrimp, crayfish, salamanders, beetles, crabs, etc. a few species have evolved eyelessness o Prediction: distantly related cave dwelling species have converged on eyelessness  QUESTION: Eyelessness:  Is cheaper than having eyes  Could be adaptive in some environments  Has evolved multiple times  Occurs in species whole close phylogenetic relatives have eyes  All of the above are true  You can use  The idea that all adaptations have costs  And  The method of planned comparisons to understand the “olfactory” paper  What is the convergence described in that paper?  QUESTION: in an adaptation evolved in 30 or 40 generations, how would that bear on the plausibility of gradualism in evolution?  It would show that gradualism is wrong  It would not show that gradualism is wrong; such outcomes are not incompatible with gradualism  Gradualism has nothing to do with the emergence of adaptations  Gradualism is not an evolutionary idea, it is a general principle of all the sciences  Primitive similarities are intentionally neglected in phylogenetic (cladistic) classification  Primitive traits are present in the ancestors of the group you are studying  They are simply the older versions of the trait, hence they occur: o Earlier in the fossil record o Earlier in development o In the out-group  Rates of evolutionary change depend on:  Amount of genetic variance (Vg)  Intensity of selection  Generation time  Mutations create new alleles  Over evolutionary time selection spreads the most beneficial alleles… o Based on their mean effects on fitness, averaged over all the contexts in which they occur  Why do social groups exist?  Why do individuals associate and interact with other members of their species?  Evolutionarily speaking, is it good for them too? o Or are they doing it to benefit the group or species as a whole?  Dynamics of social evolution  In particular, what is the entity that social adaptations are designed to benefit? o Gene? Individual? Group? PROB NOT Species? PROB NOT Eco- system? PROB NOT  Selfishness suggests that selection is not working for the good of the group as a whole, o But if it isn’t, how could altruism evolve?  Imagine a mutant gene that causes an altruistic (-+) trait  o What will happen to this gene? o It gets costs, and gives benefits to competitors o It will be selected against even though it’s good for the group/species  QUESTION: simple Darwinian natural selection is expected to favor what kinds of traits?  Cooperative only  Selfish only  Altruistic and cooperative only  Certain traits in all four quadrants (altruistic -+, cooperative ++, spiteful --, selfish +-  Selfish and cooperative only  Traits that begin with + are beneficial, while traits that begin with – are detrimental  How do altruistic traits evolve?  Kin selection o A gene gets into the next generation because it has effects on phenotypes that cause it (the gene) to get passed to offspring  Effects aren’t limited to the body the gene is sitting in  Example: A gene in Sally can get passed on by producing phenotypic effects that increase Sally’s fitness OR it could get passed on by producing phenotypic effects that decrease Sally’s fitness and increase the fitness of other individuals who carry the same gene (“fitness swap”) o What kind of “fitness swap” would yield a net payoff?  c = fitness cost  b = benefit  r = chance that the gene is shared by common descent  if rb>c, the gene gets a net benefit (Hamilton’s Rule) o example: Say Sally has a full sister; then r=1/2 o say Sally can give her sister 3 fitness unites (b=3) at a cost to herself of 1 fitness unit (c=1) o is rb>c? is ½(3)>1? YES o this is the kind of altruism that is favored by kin selection o kin selection is a model of how evolution works, not a model of how animal minds work  why aren’t b and c always equal?  What sally gives, her sister gets o But there are natural asymmetries in: exposure to danger, need, resources, ability to convert resources into offspring, age  that make b and c unequal  Many studies support this theory o There are many questions about proximate mechanisms  Example: kin recognition, evaluation of b and c o But there is very little doubt that the theory is essentially correct o Phenotypic altruism vs. genetic selfishness  Any evolutionary viable model for altruism will HAVE TO take the altruism out of it  One phenotype is nice to another but the underlying genes get a net benefit  Reciprocity Kin Selection and Recipocrity 9/22/2011 10:50:00 AM  Why do social groups exist?  Why do individuals associate and interact with other members of their species?
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