Evolutionary Basics

Evolutionary Basics

1. General evolutionary theory

   • = Inclusive fitness theory (William Hamilton, 1964; adaptations are selected for and evolve because they promote inclusive fitness; that is, genes increase their evolutionary success directly through maximizing personal fitness & indirectly by helping related individuals who share the gene)
     • classical/individual fitness (indiv.'s direct reproductive success; no. of surviving offspring)
     • indirect fitness (effects of indiv.'s action on reproductive success of genetic relatives weighted by degree of genetic relatedness)
       • explains altruism, parental care & group formation
       • altruistic behav. can be selected for if rb>c
         • discriminate in favour of relatives
     • unconscious & unintentional
     • Richard Dawkins (1979): 12 misunderstanding
       • 1) kin selection is not a special kind of natural selection to be invoked only when indie. selection fails
       • 2) is not a form of group selection (differential survival of whole groups of organisms); works on individual level; b. makes indie discriminate in favour in related individuals
       • 3) does NOT require cognitive reasoning; rules of thumb; genes >> phenotype (nervous system) >> behav. (unconscious heuristic)
       • 4) Altruism is not too complex for genes to code for it; genes interact
       • 5) All members of species share ~99% of genes but does not lead to universal altruism but siblings share only 50% of genes BY DESCENT (same copy as parent); universal altruism is not a evolu. stable strategy (indiscriminate altruists would be invaded by indiv. altruists)
       • 6) works for all genes (not just rare ones); first rare, then gene will spread to fixation >> everyone will have it
       • 7) Altruism expected bw. clones only if matriarch had gene for altruism
       • 8) Sterile worker insects don't propagate by caring for sterile worker insects that are esp. closely related b. relatives need to be able to reproduce
       • 9) Parent-offspring conflict does apply to monogamous species b. focal indiv. is more valuable than full siblings siblings
       • 10) Instead of inbreeding, could have normal child (r=.5) and a niece/nephew (r=.25) rather than inbred child (r=.75)
       • 11) Individuals help siblings more who seem more closely related - but r is probabilistic (on average 50% but can vary; physical resemblance does not necessarily ~ r)
       • 12) Better to invest 100% in most closely related indiv. than proportional to r
     • inclusive fitness = no. of offspring equivalents an indiv. rears, rescues or otherwise supports regardless of who begets them
       • e.g. Belding's ground squirrel emits alarm call that puts itself in danger but protects its relatives in local group
   • assumed to be correct (reproductively distinct species have been produced experimentally)
   • would be proven false if complex life forms were created in periods too short for evolution, or if adaptations functioned for benefit of another species or for same-sex competitors)

2. mid-level theories

   • Theory of parental investment (Trivers, 1972)
     • = the sex that invests greater resources (human females) will evolve to be choosier in mate selection; the other sex will be less choosy & more competitive w/ members of own sex for access to selective sex
     • parental investment = investment in offspring by parent that increases the offspring's chances of surviving and hence reproductive success at the expense of the parent's ability to invest in other (future) offspring
     • two categories of parental investment
       • mating investment (the sexual act & sex cells invested)
       • rearing investment (time & energy expended to raise offspring after conception)
       • both are bigger for women b. egg cell is bigger than sperm cells and there is a limited supply of ~400; fertilization & gestation occur in the woman & pose a nine-month commitment
       • invest more in mating, women more in parenting
     • different sexual strategies: males benefit from frequent mating & monopolizing access to fertile females; female benefit from choosing the male w/ the best genes & most likely to invest in them & their offspring
     • form of sexual selection
   • Parent-Offspring conflict (Robert Trivers, 1974)
     • = resource allocation that is optimal for offspring (largest possible share of parental resources) is not optimal for parent (equal distribution across offspring b. of diminishing return w/ increases in resource investment in individual offspring
   • Theory of reciprocal altruism among non-kin (Trivers)
   • Optimal Outbreeding Theory (Bateson, 1978)
     • = there is an optimal balance bw. dangers of inbreeding (homozygosity; dangerous for recessive deleterious traits that can lead to inbreeding depression) & costs of excessive outbreeding (mating w/ wrong species; hybrid incompatibility) >> should be sensitive to kinship in mate selection
       • inbreeding avoidance mechanisms; crossbreeding bw. populations enhances fitness

3. Evolutionary Psychology

   • focuses on 4 key questions
     • 1) Why is the mind shaped the way it is (causal processes that shaped it)?
     • 2) How is the human mind designed (organization, components & mechanisms)?
     • 3) What are the functions (what is it designed to do)?
     • 4) How does input from current env. interact w/ design to produce observable behav.?
   • focuses on adaptive problems & their solutions >> psychol. adaptations & their by-products
   • evolved psychological mechanisms
     • Human mind as collection of functionally specialized evolved mechanisms activated by certain contexts that generate certain behav.; evolved in response to selective pressures & adaptive prohlems
     • solved specific problem & thus increased chances of survival & reproduction
     • designed to take in a narrow, part. slice of information (cues that recurred dur. EEA)
     • = decision rules that transform input (cues) into output (physiol. activity, behav. or info to other psychol. mechanisms) that led on average to successful solution when they evolved
     • domain-general mechanisms (e.g. general intelligence, class cond., WM or analogical reasoning) developed to create novel solutions to adaptive problems that did not recur often enough in evolu. history >> handle novelty, unpredictability & variability
     • specific rather than general solution b. diff. adaptive problems have diff. solution, & general solutions are less successful & make more mistakes
     • allow flexibility
     • design features = attributes of the mechanism/adaptation

4. Theory of Natural Selection

   • Darwin observed Galapagos finches who had diverged from common ancestors b. of local ecological cond. over time into distinct species
   • there are more individuals than can survive & reproduce; three premises: variation, adaptation & inheritance
     • adaptive heritable traits have better reproductive success b. increase chances of survival & reproduction >> are passed on & become more frequent in gene pool of next generation
       • two modes
         • Natural selection
           • = adaptations that have arisen as consequence of successful survival (survival of the fittest)
             • favours traits that help organisms increase their genetic representation in future generations
               • traits increasing reproduction more imp. than survival b. survival only useful when it allows for reproduction
         • Sexual selection
           • = a mode of natural selection that operates through 2 primary means:
             • members of one biological sex choose mates of the other sex to mate with (INTERSEXUAL SELECTION); preferential mate choice >> qualities desired by mates increase in frequency
               • good genes theory: females chose males w/ best genes (inferred from phenotypic traits)
             • ...and compete with member of the same sex for access to member of the opposite sex for better mating success (INTRASEXUAL SELECTION), e.g. through direct access to mate or through controlling resources desired by mate; qualities that lead to cussess in same sex context are passed on & become more frequent
           • some individuals have better reproductive success than others because they are more attractive or prefer more attractive mates
           • explains why some evolved features are deleterious to individual survival
             • males put extreme effort into demonstrating their fitness >> be chosen by female
               • sexual dimorphism in secondary sexual characteristics (e.g. lions' manes, deers' antler or peacocks' tale)
           • = adaptations that have arisen as a consequence of successful mating
         • two classes of adaptations
           • survival advantage
           • mating advantage
           • both stem from differential reproductive success by virtue of heritable differences in design
     • there is VARIATION in physical & behav. traits (phenotype; some are more adaptive)
     • some variations are INHERITED (genotype); only those are relevant to NS
     • some indiv. leave more offspring (SELECTION) b. heritable traits help them survive & reproduce leading to differential reproductive success (ADAPTATION)
   • Natural selection is primary cause of evolutionary change (through differential survival & reproduction of indiv. due to diff. phenotype based on genotype) & only known cause of adaptations
     • Other causes of evolu. change:
       • mutations (random changes in DNA)
       • founder effect (unrepresentative portion of popu. establishes colony)
       • bottle neck (popu. shrinks b. of random catastrophe)
     • Evolution by natural selection is
       • unintentional & unplanned
       • gradual
       • requires partial adaptations that are advantageous
       • applies to (social) behav. b. all behav. require an underlying physical structure
       • Acts on individual > group
   • Misunderstandings
     • genetic determinism (behav. controlled by genes cannot be influenced by env.)
       • but human behav. occurs b. of evolved adaptations that require env. input to develop & be situationally activated
       • can change evolutionarily evolved behav. by educating about mechanism & change env. input that triggers deal & activation of behav.
       • adaptations are polygenic & interact
     • Current mechanisms are optimally designed
       • evolutionary time lag (are designed for selection pressures of previous env.)
       • selection favours mechanisms when benefits > costs relative to alternatives; if adaptations solved problem 100% of time, costs would be too high >> work reasonably well on average
       • novel env. stimuli that approximate cues that adaptations evolved to detect can hijack evolved psychol. mechanisms; e.g. porn
       • mismatch bw. modern & ancestral env. >> lower adaptive utility; e.g. modern diet; stress response; fear of snakes > guns
     • Just-so stories
       • DeBruine (2009): Philosopher Jerry Fodor (2007) criticised evolu. explanations of behav. as inherently post-hoc
         • other disciplines do that too
         • evolu. psych. can generate novel, testable hyp. about human behav. that would otherwise not be investigated & can sometimes predict behav. better than other theories
           • Prediction: NVP or food taboos adaptive
         • considering costs & benefits of behav. on genetic fitness
       • = untestable hypotheses >> challenging status pf evolu. psych. as empirical science
         • e.g. first tools likely made from plant materials which decay too quickly to leave evidence >> can only make educated guesses
         • afterlife/God exists OR God instinct
         • female orgasm as adaptation or side-effect of male orgasm
       • Confer et al. (2010): generate testable predictions from hyp.; example of falsified hype.: kin altruism theory of homosexuality (indiv. w/ low heterosexual mating prospect don't shift from direct mating effort to investing in kin, e.g. through greater generosity, financial & emotional investment & willingness to give gifts to kin)
         • example: NVP as byproduct of prenatal hormones predict diff. pattern of food aversions than maternal & embryo protection hyp.; these predictions can be empirically tested w/ different methods
       • = adaptive explanations for the evolution of a given traits that do not rest on evidence beyond their own internal logic
       • Machery: there is uneven quality of research as in every field but little reason to endorse a principled criticism toward evolutionary psych
       • Jonathan Gottschalk: All evolutionists shape hypotheses in the form of historical narratives but they test for weaknesses in their favourite stories; make predictions that can be tested; Big Bang Theory was criticized as just-so story b. of its likeness to biblical genesis & grandeur of religious myth
     • Massive modularity//Why not domain general rationality mechanisms > specialised adaptations?
       • paternity uncertainty hyp.: men's jealousy triggered by cues of sexual infidelity even if partner is on contraceptive pill)
       • failure to predict
       • combinatorial explosion (predictability & rapidity of response hint at dedicated psychol. adaptation b. more efficient & faster than deliberate evaluation of all alternatives)
       • poverty of stimulus problem (indiv. cannot learn statistical regularity ontogenetically b. would take a lot of cases of female infidelity & waiting for pregnancy)
       • what is rational differs across adaptive problems
     • Practical value: not treating NVP? Relying on food taboos
     • some practices reduce reproductive fitness (suicide, homosexuality)
     • lack of knowledge of many selection pressures & ancestral env.
     • political & ethical implications
     • evolutionary psych as anthropogenic
     • role of learning, culture & socialisation
   • Environment of evolutionary adaptedness
     • = all the selection pressures (adaptive problems) present during the adaptation's period of evolution responsible for producing this adaptation
     • each adaptation has its own EEA
     • period of evolution = time span dir. which adaptation was constructed until it became universal design of species
   • reproductive success = passing of genes onto the next generation in a way that they too can pass on those genes
   • Evolution = change of heritable traits of a popu. over time
   • Evolu. success = leaving behind the maximum number of copies of genes in popu.

5. Products of evolution

   • ADAPTATIONS (inherited & reliably developing characteristics caused by NS b. solved adaptive problems & thereby contribute dir. or indir. to successful survival & reproduction; e.g. umbilical cord)
     • which attributes are adaptations?
       • reliability (regularly develop in all members of species or one sex across "normal" env & perform in contexts in which it is designed to function)
         • can develop after birth but non-transient, temporary or easily disturbed
       • efficiency (solves adaptive problem well)
       • economy (benefits > costs)
       • precision (solve a specific adaptive problem)
   • BY-PRODUCTS of adaptations (do not solve adaptive problems but coupled w/ adaptations; e.g. belly button)
   • RANDOM EFFECTS (chance mutations or chance events; not species-typical & not linked to adaptations)
   • Adaptive problems: survival, reproduction & sociality

6. Specific Evolutionary Hypotheses

   • = propose existence of a specific psychol. mechanism that is designed to solve a specific human adaptive problem (function)
   • predictions that follow can be empirically tested
   • more precise hyp. better
   • if prediction wrong, hyp. can still be correct; if hyp. is wrong, theory could still be correct

7. Learning & Socialization

   • mind is not a blank slate; learning requires evolved psychol. adaptations
     • learning adaptations
       • learned incest avoidance (coresidence as reliable cues of close genetic relatedness)
       • learned food aversion
       • learned prestige criteria for selective learning from model
       • = require specific set of cues as env. input, have diff. functional output & solve diff. adaptive problems
   • evolu. selection pressures shape phylogenetically evolved mechanisms; env. input influences ontogenetic dev. & activates adaptations at proximate level

8. Levels of explanation (Tinbergen's Four Whys)

   • Proximate
     • Ultimate
   • Dynamic view
     • Ontogeny (dev.; hormones, genes or social learning)
       • Phylogeny (evolu.; evolved out of other mammals)
   • Static view
     • Mechanism (causation; e.g. nervous system)
       • Function (adaptation): nursing promotes survival