Sperm competition

Another insight from Sex at Dawn:

"Why do so many heterosexual men get off on pornography featuring groups of guys having sex with just one woman?  Researchers have confirmed what porn producers already know: men tend to get turned on by images depicting an environment in which sperm competition is clearly at play.  Images and videos showing one woman with multiple males are far more popular on the internet and in commercial pornography than those depicting one male with multiple females.  Why would the males in a species that's been wearing the shackles of monogamy for 1.9 million years be sexually excited by scenes of groups of men ejaculating with one or two women?" (Page 229)

The traditional theory of male competition is that men compete, not their sperm.  The winner of the personal struggle gets to impregnate the most females.  This is of course the gorilla model, where the male is twice the size of the female, and is polygynous (has a harem).  But suppose men cooperate, and instead their sperm competes?

They point also to:

1. Men climax much quicker than women
2. Women can have multiple orgasms; men need a bit of a break before they're ready to fuck again
3. The shape of the coronal ridge and the glans is unique to man; this shape is effective in pulling back previously deposited sperm, with extended repeated thrusting
4. Man has the longest and fattest cock of all the great apes
5. A human ejaculation consists of 3 to 9 spurts; the early spurts contain protective chemicals; the later ones a spermicidal substance--logical only if multiple male partners are the biological norm
6. Daily ejaculation dramatically reduces DNA damage to men's sperm cells, thereby increasing male fertility
7. Rapid-reaction DNA controlling development of testicular tissue, this DNA being absent in monogamous or polygynous primates
8. Human (and bonobo) sexual activity goes far beyond what's needed for conception,  with more than 1000 copulations per birth
9. Female Copulatory Vocalisation. i.e., the noise women make during orgasm makes no sense if we are monogamous, never mind the danger such a racket would make in a jungle full of large predators
10. Why do women have orgasms at all?
11. Human hypersexuality.
12. Testicular volume and libido far beyond what's needed for monogmaous or polygynous mating
13. There is evidence that the woman's body chooses which man's sperm to accept by releasing chemicals
14. The precarious location of the testicles in a vulnerable external scrotum, associated with promiscuous mating  

Such an interesting book.  The squeals of outrage which greeted its publication rather suggest it's essentially right.

[See also Sex at Dawn]