1. Parental Investment and Sex Differences in Sexual Behavior
Evolutionary perspective on origins of sex differences.
Parental investment theory.
Sexual strategies theory.
Additional research on sex differences and flexibility.
Additional implications.
Error management; regrets; interactions with kin.

2. Parental Investment and Sex Differences in Sexual Behavior
Evolutionary perspective on origins of sex differences.
Parental investment theory.
Sexual strategies theory.
Additional research on sex differences and flexibility.
Additional implications.
Error management; regrets; interactions with kin.
3 things to be mindful of…

4. [ stereotypes ]

5. [ the naturalistic fallacy ]

6. Responses to intimate invitations.
Dinner
Apartment
Bed
Man asks;
Woman responds
Woman asks;
Man responds
(Clark & Hatfield, 1989)

7. Minimum standards for dating and mating.
(Kenrick et al., 1990)

8. Sex differences in sexual behavior…
In general: Compared to women, men are more “eager.”
Compared to men, women are more cautious and choosy.
Why?
Evolutionary perspective on origins of sex differences…

9. Parental investment.
“…any investment by the parent in an individual offspring that increases the offspring’s chance of surviving (and hence reproductive success) at the cost of the parent’s ability to invest in other offspring.”
(Trivers, 1972)
Costs of parental investment include reduced opportunities to make more offspring (“mating / parenting trade-off”).
This has implications for understanding the evolution of sex differences in mating behavior.

10. Parental investment theory
Background: In sexually-reproducing species…
Sex differences in reproductive anatomy.
Sex differences in obligatory parental investment.
Sex differences in number of offspring that can possibly be produced.
Specific implications:
Sex with greater obligatory investment is more cautious and more choosy in the context of sexual decision-making.
Sex with less obligatory investment is more competitive for access to choosy mates.

11. Sexual strategies theory.
Evolution of both long-term and short-term mating strategies.
Long-term: cautious, choosy, monogamous, etc.
Short-term: eager, not-so-choosy, promiscuous, etc.
Biological basis for each strategy.
Different costs and benefits associated with each strategy.
Costs & benefits differ, depending on context.
Implies variability and flexibility.
Individual differences.
Flexibility depending on immediate situation.
Variability across life-span.
Sex differences.
Dawkins:
“An average gene will spend approximately half its time sitting in male bodies and the other half sitting in female bodies.”
“In whichever of the two sorts of body it finds itself, we can expect a gene to make the best use of the opportunities offered by that sort of body. These opportunities may well differ according to whether the body is male or female.”

12. in 52 countries around the world…
Additional research on sex differences and flexibility.
Data from 16,288 people
in 52 countries around the world…
(Schmitt et al., 2003)

13. Number of sexual partners desired “in the next 30 years”:
(Schmitt et al., 2003)

14. Percent who desire more than one sexual partner “in the next 30 years”:
(Schmitt et al., 2003)

15. Current relationship status
Percent who desire more than one sexual partner “in the next month”:
Current relationship status
% of men
% of women
Married
12.8
3.5
Cohabitating
18.2
2.4
Dating one person exclusively
19.0
2.7
Not currently involved
28.6
6.2
Sexual orientation
% of men
% of women
Heterosexual
25.4
4.4
Homosexual
29.1
5.5
Bisexual
30.1
15.6
(Schmitt et al., 2003)

16. Adaptive flexibility:
One example: Impact of sex ratio within local population:
(Stone et al., 2007)
When ratio of men:women is higher (men outnumber women)…
- Men become even less choosy.
- Women become even more cautious and more choosy.

17. Some additional implications:
Error management
Regrets
Interactions with kin.

18. Error management theory
Natural selection favored the evolution of cognitive biases that minimize the likelihood of making especially costly errors.
(Even if those biases produce more frequent errors of other kinds.)
(Haselton & Buss, 2000)
Implications for mens’ misperceptions of womens’ romantic interest…
Men over-estimate women’s romantic interest.
(This happens only when the women are perceived to be plausible mates.)
Implications for womens’ misperceptions of mens’ relationship commitment…
Women under-estimate mens’ commitment to a long-term relationship.

19. Romantically interested “Romantically interested”
Reality
Judgment
Romantically interested
Not interested
“Romantically interested”
Correct
Error
“Not interested”
Small fitness costs
Bigger fitness costs
Cognitive bias
(men perceiving women)

20. Committed for the long-term
Reality
Judgment
Committed for the long-term
Not committed
“Committed for
The long-term”
Correct
Error
“Not committed”
Big fitness costs
Smaller fitness costs
Cognitive bias
(women perceiving men)

21. Regret: Regrets in the domain of sexual behavior…
(Galperin et al., 2013)
Women especially regret specific sexual actions.
Men especially regret specific sexual inactions.

22. (Lieberman, Pillsworth, & Haselton, 2011)
Interactions with kin:
Lots of mammals: Fertile females avoid male kin.
Humans: Fertile females avoid fathers.
(Lieberman, Pillsworth, & Haselton, 2011)