The Influence of Natural Selection

1
The Influence of Natural Selection
2
Major Point

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

3
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

4
Natural Selection

• any genetically influenced characteristic that
  increases an individuals 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

5
The Concept of Fitness

• Fitness
• refers to how many copies of the individuals
  genes are passed on to future generations
• the more surviving offspring you produce, the
  more fit you are

6
Inclusive Fitness

• idea that fitness includes not only ones own
  offspring, but also the offspring of those who
  share ones 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 ones family, tribe, or
  clan

7
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

8
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

9
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

10

• 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

11
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

12
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

13
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

14
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

15

• 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.

16
Sexual Jealousy

• Evolutionary psychology views jealousy as a
  mechanism that is designed to prevent ones 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

17
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.