Understanding Male Sex Drive and Sperm Wars: An Evolutionary Perspective

1. Chapter 7 Male Sex Drive

2. Sperm Wars (Baker, 1996) • Male sexuality evolved to prevent/fight sperm warfare • Maximize chance of fertilizing egg, passing genes on, & avoiding cuckoldry • Penis anatomy, thrusting & rapid orgasm • Routine sex & topping off • Masturbation • Infidelity & jealousy

3. Penis Anatomy & Thrusting • Shape/thrusting cleans out other sperm • Suction • Larger the greater the suction • Rapid orgasm • Maximized insemination • Animals: Rapid insemination after infidelity • Why males find pornography so arousing

4. Penis Anatomy & Thrusting • Reproductive disadvantage to male for female to have orgasm before sex • Increases strength of cervical filter • Males biologically destined to ‘rush’ w/o foreplay, climax rapidly

5. Nature of Sperm • Average ejaculate contains 500 million sperm • 3 primary types: • Killers (fast, youngest, poison head) • Seek out and kill other men’s sperm • Blockers (slow, old) • Block other men’s sperm • Egg-getters • > 99% of sperm in ejaculate are killers or blockers • < 1% of sperm are egg-getters

6. Nature of Sperm • Sperm live 5 days in female • 2 days to peak fertility • Egg dies w/in 1 day of release • Male must inseminate 3-4 days < ovulation • Best chance of conception if 2-3 days before • Sufficient killers & blockers to win sperm war

7. Routine Sex & Topping Off • Hidden ovulation: Males consistently inseminate partner • Higher sex drive • Males adjust #, type sperm to keep healthy, fresh sperm in cervix (top off) • Delay since last sex (chance of foreign sperm?) • 5 days: 400 million • 3 days: 200 million • 3 hours: 30 million

8. Routine Sex & Topping Off • Critical to winning sperm wars • Keep killer, blocker sperm population high • For 3 days post-intercourse • Aging of sperm in testes matches loss of blockers in cervix • Inject exactly the right amount of blockers to top off population

9. Routine Sex & Topping Off • Columns of sperm in epitidymis • Closest to testicles youngest • Farthest away oldest (blockers, killers) • Adjust sperm via muscular contractions, number of spurts

11. Masturbation • 98% males masturbate (3/wk, Class M = 4.89) • Many mammals also • Shedding sperm • Testes produce 300 million sperm/day • Shed 5 million/hour since last ejaculate • First to be ejaculated oldest

12. Masturbation • Male body times urge to maximize chance of winning sperm wars • Purpose is to tailor ejaculate for next intercourse • Adjusting type, number of sperm • Shedding old, slower sperm • Best 2 days < insemination • Many young killers & blockers • Can be further adjusted depending on infidelity risk

13. Infidelity & Jealousy • Sexually jealous/possessive of partners • Most jealous/in control less chance of cuckoldry • More HIS genes passed on • Male sexuality evolved w/ desire for numerous, fertile partners (even strangers)

14. Item Long Shortp IQ 3.28 7.07 < .05 Emotional Stability 4.10 6.34 < .05 Honesty 3.17 6.07 < .05 Wealth 8.90 8.14 ns Health 6.48 4.10 < .05 Kind 3.93 6.10 < .05 Weight 5.52 2.69 < .05 Religion 7.48 4.19 < .05 Race 7.38 6.24 < .05 Attractive 3.00 1.24 < .05 Height 8.28 4.93 < .05 Family 9.83 10.17 ns

15. Male Sex Drive • Men want lots of sex w/ lots of partners • Relationships are better but still... • Men want 50% more sex than they are having • Women sex desire = actual amount

16. Sexual Starvation • Chronic sexual frustration inevitable for most men • High status males may be able to achieve satisfaction (Brad Pitt, Bill Gates) • Temporary

17. Adaptation • Habituate to any S intensity • Taste, touch • Incrementally decrease R • Incrementally increase desired S • Money, Sports, Drugs • Lottery winners initial euphoria fades • Jordan & multiple championships • Pot gateway drug

18. Adaptation

19. Sexual Starvation • Sex • Virgins just want 1 • Then after 1 you just want 2-3 and so on • Made worse by social comparison (Festinger) • Compare w/ others to evaluate ourselves • Men may lie or be inaccurate • Volunteers different than non-volunteers • Media distorts sexual experiences of males

20. Sexual Starvation • Males will never be sexually satisfied because no matter how much sex they have they will eventually adapt & want more • Doomed to be perpetually frustrated • Sexual boredom (males > females) • More masturbation & risky sex (prostitutes, unprotected sex, cheating) • Desire for big pay-off increases risk taking

21. Reaction Paper III: Sexual Starvation • What is your reaction to the idea that men are fatally doomed to experience chronic sexual frustration, not getting enough sex even when married? • How do you think this will impact the way you deal w/ relationships in the future?

22. Conclusion • Male sex drive complicated & may have evolved to prevent/fight sperm warfare • One consequence is high sex drive and perpetual sexual starvation via habituation