The influence of natural selection
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The Influence of Natural Selection. Major Point. many gender differences in sexual behavior may be the result of natural selection. How Evolution Works. Living things produce more offspring than the environment can sustain These offspring differ in genetic make-up

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The Influence of Natural Selection

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The influence of natural selection

The Influence of Natural Selection


Major point

Major Point

  • many gender differences in sexual behavior may be the result of natural selection


How evolution works

How Evolution Works

  • Living things produce more offspring than the environment can sustain

  • These offspring differ in genetic make-up

  • Characteristics that confer an advantage in term of survival and reproduction will be passed on to the next generation


Natural selection

Natural Selection

  • any genetically influenced characteristic that increases an individual’s chances of survival and reproduction will become more numerous in subsequent generations

  • example

    • if dark brown skin makes salamander less visible to predator, that salamander will be more likely to live long enough to reproduce

    • salamander will pass on genes that code for dark brown skin to its offspring


The concept of fitness

The Concept of Fitness

  • Fitness:

    • refers to how many copies of the individual’s genes are passed on to future generations

    • the more surviving offspring you produce, the more fit you are


Inclusive fitness

Inclusive Fitness

  • idea that fitness includes not only one’s own offspring, but also the offspring of those who share one’s genes

  • example:

    • if you take a personal risk to defend or protect your sister, this may help her survive and reproduce

    • your sister shares 50% of your genes

  • explains tendency to help one’s family, tribe, or clan


Evolutionary psychology

Evolutionary Psychology

  • is concerned with how various psychological mechanisms promoted fitness in the ancestral environment

    • environment that existed during time that our species was evolving

  • attempts to understand

    • why behavioral tendencies exist

    • understand function of behavior in enhancing survival and reproduction


Human sexuality

Human Sexuality

  • certain gender differences in sexual behavior may be the result of natural selection

    • what increases fitness for men is not necessarily what increases fitness for women


Minimum parental investment

Minimum Parental Investment

  • men and women differ in minimum parental investment

    • for men, minimum parental investment is low

    • for women, minimum parental investment is high


The influence of natural selection

  • differences in minimum parental investment lead to different mating strategies

  • males prefer

    • multiple mates

    • young, healthy mates

  • females prefer

    • mates with capacity and willingness to expend resources on them and their offspring


Desire for casual sex

Desire for Casual Sex

  • Oliver & Hyde (1993)

    • conducted meta-analysis of studies on attitudes toward sexual behavior

    • found large sex difference in attitudes toward casual sex

    • men have more favorable attitude

  • Erlichman & Eichenstein (1992):

    • conducted study of “private wishes”

    • 25% of men and 5% of women ranked “having sex with anyone I chose” as #1 private wish


Desired number of partners

Desired Number of Partners

  • Buss & Schmitt (1993)

    • asked unmarried college students how many sexual partners they would like to have in the next month, year, lifetime, etc.

    • found that, at every time interval, men desired more partners

    • example

      • within next month: women = 1, men = 2

      • within lifetime: women = 4 or 5, men = 18


Preference for physically attractive partner

Preference for Physically Attractive Partner

  • Note: many components of physical attractiveness are cues to youth and health (fertility)

  • Many studies have found that youthful complexion, firm muscle tone, lustrous hair, and full lips are desired by men

  • Pattern not limited to our society

  • Physical appearance of desired mates is far more important to men than to women


Preference for partners with resources

Preference for Partners with Resources

  • Note: dominance and status are cues to resources

  • Research suggests that women prefer men with status in a dominance hierarchy

  • Buss (1989):

    • in all of 37 cultures studied, women valued wealth and status in men more than men valued it in women


The influence of natural selection

  • Kenrick et al. (1994)

    • showed subjects photographs and personality profiles, then asked subjects to indicate current level of commitment to romantic partner.

    • For men, viewing photo of physically attractive woman reduced level of commitment.

    • For women, viewing profile of socially dominant man reduced commitment.


Sexual jealousy

Sexual Jealousy

  • Evolutionary psychology views jealousy as a mechanism that is designed to prevent one’s mate from engaging in behaviors that threaten reproductive fitness.

  • For a male, threat comes from his mate getting pregnant by another male

  • For a female, threat is that mate will shift his resources from her and her offspring to another female, or even abandon her altogether


Research on jealousy

Research on Jealousy

  • Buss et al. (1992)

    • asked subjects which would upset them more (1) partner forming deep emotional attachment to another person or (2) partner enjoying passionate sex with that person.

  • Found

    • 60% of males more upset by sexual infidelity, 40% more upset by emotional infidelity.

    • 17% of females more upset by sexual infidelity, 83% more upset by emotional infidelity.


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