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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
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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
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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
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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
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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
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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
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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