Lecture 5: evolution
Chapter 8 (in class)
Natural selection
● Naturally occurring variation leads to differences in the ability to survive and
reproduce (reproductive success)
○ The next generation contains more of the successful variant
● Thus, successful variants are selected and unsuccessful variants are weeded out
● Over time, successful variants come to characterize entire species
Adaptations: inherited solutions to survival and reproductive problems posed by hostile
forces of nature
The primary products of selection defined as reliably developing structure in the
organism which, because it meshes with the recurrent structure of the world, causes the
solution to an adaptive problem
Adaptive problem: anything that impedes survival or reproduction
Byproducts of adaptations and noise
● Byproducts of adaptations: incidental byproducts
○ Consequences of adaptations
● Noise or random variation
○ Introduced through the gene pool through mutations, do not impede the
function of adaptations
Sexual selection
● Many mechanisms seems to threaten survival
○ Peacock’s elaborate plumage
● Evolution by sexual selection as solution
○ These traits evolved because they contributed to an individual’s mating
success
■ IntrAsexual competition: members of the same sex compete with each
other for sexual access to members of the other sex
■ IntErsexual competition: members of one sex choose a mate based
on their preferences for particular qualities in that mate
● Genes and inclusive fitness
○ Discovery of the gene as a unit of inheritance led to key discovery, that
natural selection and sexual selection are different forms of the same process
■ Differential gene reproduction: reproductive success relative to others
○ Inclusive fitness theory (Hamilton, 1964)
■ Personal reproductive success (number of offspring you produce) plus
effects you have on the reproduction of your genetic relatives,
weighted by genetic relatedness
Human nature
● Need to belong
● Helping and altruism
● Universal emotions
● Depression
, Sex differences
● Males and females will be the same or similar in all domains where sexes have faced
the same or similar problems
● Males and females will be different in those domains where sexes recurrently faced
different adaptive problems
● Jealousy
○ Men over evolutionary history have risked investing in children who were not
their own
○ Men should be more jealous in response to cues in sexual infidelity
○ Women should become more distressed over a partner’s emotional infidelity
Featured study
● Students (264) completed surveys faced with several forced-choice dilemmas:
ìE.g., what would upset you more?
ìSexual infidelity
ìEmotional infidelity
ìResults:
ìMen, relative to women, find it more difficult to forgive a sexual infidelity than
emotional infidelity
ìMen, relative to women, are more likely to terminate a current relationship following
a partner’s sexual infidelity than emotional infidelity
Desire for sexual variety
Featured study
● Clark and Hatfield (1989)
ìMembers of the sex that invests less in offspring, are predicted to be less
discriminating in their selection of mates & more inclined to seek out multiple mates
Evolutionary theory predicts that men are more inclined to seek multiple mates to
increase their reproductive success
The big 5 and evolutionary-relevant adaptive problems
● The big 5 personality traits as clusters of key features of adaptive landscape of other
people
● Humans have evolved difference-detecting mechanisms designed to notice and
remember individual differences that have most relevance for solving adaptive
problems
Limitations of evolutionary psychology
● Evolution has a large time span
● Can’t go back in time/testability
● Precise selective forces
● Modern conditions do not equal ancestral conditions
Chapter 8 (in class)
Natural selection
● Naturally occurring variation leads to differences in the ability to survive and
reproduce (reproductive success)
○ The next generation contains more of the successful variant
● Thus, successful variants are selected and unsuccessful variants are weeded out
● Over time, successful variants come to characterize entire species
Adaptations: inherited solutions to survival and reproductive problems posed by hostile
forces of nature
The primary products of selection defined as reliably developing structure in the
organism which, because it meshes with the recurrent structure of the world, causes the
solution to an adaptive problem
Adaptive problem: anything that impedes survival or reproduction
Byproducts of adaptations and noise
● Byproducts of adaptations: incidental byproducts
○ Consequences of adaptations
● Noise or random variation
○ Introduced through the gene pool through mutations, do not impede the
function of adaptations
Sexual selection
● Many mechanisms seems to threaten survival
○ Peacock’s elaborate plumage
● Evolution by sexual selection as solution
○ These traits evolved because they contributed to an individual’s mating
success
■ IntrAsexual competition: members of the same sex compete with each
other for sexual access to members of the other sex
■ IntErsexual competition: members of one sex choose a mate based
on their preferences for particular qualities in that mate
● Genes and inclusive fitness
○ Discovery of the gene as a unit of inheritance led to key discovery, that
natural selection and sexual selection are different forms of the same process
■ Differential gene reproduction: reproductive success relative to others
○ Inclusive fitness theory (Hamilton, 1964)
■ Personal reproductive success (number of offspring you produce) plus
effects you have on the reproduction of your genetic relatives,
weighted by genetic relatedness
Human nature
● Need to belong
● Helping and altruism
● Universal emotions
● Depression
, Sex differences
● Males and females will be the same or similar in all domains where sexes have faced
the same or similar problems
● Males and females will be different in those domains where sexes recurrently faced
different adaptive problems
● Jealousy
○ Men over evolutionary history have risked investing in children who were not
their own
○ Men should be more jealous in response to cues in sexual infidelity
○ Women should become more distressed over a partner’s emotional infidelity
Featured study
● Students (264) completed surveys faced with several forced-choice dilemmas:
ìE.g., what would upset you more?
ìSexual infidelity
ìEmotional infidelity
ìResults:
ìMen, relative to women, find it more difficult to forgive a sexual infidelity than
emotional infidelity
ìMen, relative to women, are more likely to terminate a current relationship following
a partner’s sexual infidelity than emotional infidelity
Desire for sexual variety
Featured study
● Clark and Hatfield (1989)
ìMembers of the sex that invests less in offspring, are predicted to be less
discriminating in their selection of mates & more inclined to seek out multiple mates
Evolutionary theory predicts that men are more inclined to seek multiple mates to
increase their reproductive success
The big 5 and evolutionary-relevant adaptive problems
● The big 5 personality traits as clusters of key features of adaptive landscape of other
people
● Humans have evolved difference-detecting mechanisms designed to notice and
remember individual differences that have most relevance for solving adaptive
problems
Limitations of evolutionary psychology
● Evolution has a large time span
● Can’t go back in time/testability
● Precise selective forces
● Modern conditions do not equal ancestral conditions
