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 (1831-1836)

• 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