PSY 380: Introduction to Social Psychology

March 30, 2000

Evolutionary Psychology (Redux) and Human Mating

Guest lecturer: Matt Keller

Part I. What is Evolutionary Psychology?

Study of how evolutionary processes shaped human nature

Often studies cross-cultural universal behaviors

"Stone Age Minds in the Modern World"

Part II. Evidence for Evolution

Fossil record

Structural similarities

Observations of micro-evolution

Genetic mapping

No other theory has been able to explain biological phenomena

Tree of Life

Phylogenetic Tree obtained from genetic mapping

Part III. Evolutionary Theory & Animal Behavior

The major force is Natural Selection:

Differences in traits affect ability to compete for limited resources

Animals with "adaptive" traits reproduce more

Thus these traits increase in frequency over many generations

Inclusive Fitness

Inclusive Fitness: the effect on one's own RS and the RS of relatives (weighted by relation)

Animals behave in ways that (on average) have maximized their inclusive fitness in the past

Example

Belding Ground Squirrels - females tend to emit risky predator alarm calls when they are near close relatives, but not when near unrelated squirrels

Parental Investment Theory

The sex that invests more in offspring (usually females) will be choosier about who they mate with

The sex that invests less in offspring (usually males) will compete for access to the sex investing more

Evidence for the Theory

Most male animals invest less in offspring than females, and thus compete for mates more and are less discriminating

This trend increases the less that males invest in offspring

e.g., elephant seals

Animals with opposite sex roles underscore the general rule

seahorse, some birds, some insects

Parental Investment Theory - Women

Females pay much larger obligatory cost in reproduction than males (pregnancy, nursing)

So we should predict females have evolved a psychology that is more discriminating with mates and more cautious with regard to casual sex

Parental Investment Theory - Men

Males pay very little obligatory cost for reproduction

Male inclusive fitness could have been aided by casual sex, so we predict males have an evolved psychology that is less choosy

Evidence

1) Prostitution and pornography - across cultures is always dominated by male desires

2) Fantasies - across cultures, men have twice as many sexual fantasies

men fantasize about number and novelty

women more often about current partners

Will you go out on a date with me?

males

females

Will you come over to my apartment?

males

females

Will you have sex with me?

males

females

A further consequence of Parental Investment

Unlike females, males cannot know whether it is their genetic material that is passed on to the offspring. Thus, males will be "concerned" about paternity

Scoops and post-copulatory plugs in insects

Many male animals often will guard their mates after insemination

Evidence in Humans

Human males are high in parental investment, so they are very "concerned" with paternity:

1) cross cultural double standards in adultery law and social conventions

2) claustration of women (and not men) in many cultures, and most strenuous during peak reproductive potential

3) Experiment. Buunk, et al (1996). Cross cultural jealousy differences in sexes: What type of infidelity, emotional or sexual, is more disturbing?

Summary of Sex Roles in Humans

Sex differences are predicted from evolutionary theory, are found where expected in the animal kingdom, including humans

But much more is similar between the sexes than is different (need for friendship, cognitive ability, etc.)

Part IV. Common Misunderstandings of Evolutionary Psychology

1) Evolutionary Psychology is all about sex differences.

2) Because it is "natural" or "evolutionary", that makes it OK to do it

3) Evolutionary explanations imply that the behaviors cannot be changed ( "Innate" ,"Inflexible")

4) Evolutionary Psychology says all people are like the way described

5) People are consciously trying to maximize reproductive success

Take home message

Evolution has shaped animal (& human) behavioral tendencies for millions of years

These behavioral tendencies (in the form of motivations) are still with us today

Please pick up additional information handout on your way out.