Psychology 403: Topics in Evolutionary Psychology Dr. M.R. Snyder

Evolutionary Psychology The approach Old application, new formalization

Evolutionary Theories Why/how do new organisms develop? What drives change?

Evolutionary Psychology Multidisciplinary approach About 20 years old as a formalized field Theoretical approach Cosimides & Toobey (1992) –“Evolutionary Psychology Manifesto”

Evolutionary Theories Not New Greeks –Heraclitus (6th C. BC) State of flux –Aristotle (4th C. BC) Development in prescribed direction Medieval Europe –St. Thomas Aquinas (13th C) Human/lower animal differences

Eighteenth Century George Leclerc, Comte de Buffon –Adaptations to fit environment pressures Erasmus Darwin –Role of sexual reproduction Jean de Lamarck –Inheritance of acquired characteristics Georges Cuvier –Catastrophism

Charles Darwin Provided causal mechanism Voyage of the Beagle ( ) On the Origin of Species (1859) Variation, inheritance, selection Artificial, natural, sexual Differential reproductive success

Social Darwinism Late 19th century to present Directed, purposeful Teleological Political, social agenda

Sociobiology E.O. Wilson Systematic study of the biological basis of social behaviour

Evolutionary Psychology Issues Are humans unique animals? Gradual or sudden development? Modularity of mind, or general information processor? Environment of Evolutionary Adaptiveness (EEA)

Approaches Evolutionary Psychology –Will the real EP please step forward? Dual Inheritance Theory (DIT) Human Behavioural Ecology (HBE)

Terms and Concepts

Genetics Mendellian genetics –Gene, alleles –Particulate inheritance –Dominant or recessive –Homozygous or heterozygous –Genotype and phenotype Polygenetic effects Interaction between genes and environment

Darwinian Selection Adaptive, maladaptive, neutral Success –Not number of offspring, but number of reproducing offspring Gene, individual, or group as level of selection?

Natural Selection Survival value Predator/prey, environment, parasitism, etc. “Survival of the fittest”

Sexual Selection Intrasexual selection –Within a sex Intersexual selection –Between sexes

Genetic Diversity Heterozygosity Variability of offspring in the population Disease vector Sexual vs. asexual reproduction

r Values Genetic relatedness Probability of having the same gene due to common ancestor r = 1.0 –Self, identical twins r = 0.5 –Parent and child, siblings r =0.25 –Grandparent and grandchild

Inclusive Fitness William Hamilton Classical (direct) and “indirect” fitness Role of r values –rB>C –Phenotype and genotype

How to be Successful Increase classical fitness Increase inclusive fitness Quantity vs. quality tradeoff

Male vs. Female Reproduction Energy investment Commonalities Differences

Adaptationist Approach

Traits An aspect of an organism’s phenotype Physiological, behavioural

Adaptations Process by which evolution modifies and generates traits that effect the spread of some genes over others The end product of the process; i.e., the traits selected by the evolutionary process

Spandrels Byproducts Not all traits are directly selected for These traits are linked to other traits that were adaptations

Energy Finite Cost/benefit Energy budgets require trade-offs Expectation is that evolution selected for adaptations to energy budget that allows for maximization of fitness

Identifying Adaptations Traits show “special design” if they perform a specific function well, and It is difficult to postulate an alternative evolutionary process that led to the trait except for selection for this function Inferential

Attractiveness as an Adaptation Particular traits perceived as attractive by opposite sex Benefits individuals’ reproductive fitness Symons (1995): “Beauty is in the adaptations of the beholder.”

Selection Benefits for Attractiveness Genetic and resource benefits Selection favoured those who possessed traits that predisposed them to mate with others who possessed traits that provided the benefits Sexually selected traits

Cross Cultural Value Buss (1989) surveyed from 37 cultures world wide Value of physical attractiveness rated highly Industrial, first world Traditional (e.g., Ache of Paraguay, Shiwiar of Equador, etc.) Also, cross-cultural agreement on who is attractive

Sexual Selection A feedback system One sex develops preference for trait If it increases differential reproductive success, preference for trait spreads to offspring Members of opposite sex that have the desired trait will also, therefore, spread the trait to their offspring

Intrasexual Selection Competition between members of the same sex Usually, perceived as male-male –Polygynous mating systems However, in humans both male and female intrasexual selection

Intersexual Selection Choice between the sexes Sometimes called, “female choice” Reproductive costs generally more expensive for females (limiting reproductive resource)

Mutual Mate Choice Seen in species where both sexes invest heavily in offspring Both sexes are selected to display desired traits Seen in humans across time and cultures

Signaling Quality Traits Traits that indicate something about an individual’s fitness Honest signals are costly (Zahavi 1975) “Handicap principle” If you can afford the handicap, you must be of superior quality

Sensory Bias May be a bias towards some trait in sensory system May have nothing to do with mate choice However, may inadvertently influence mate selection Genes for some trait may be “piggybacked” into gene pool due to genes for sensory bias