Sex at Dawn полностью

Although Darwin might have been “perplexed” by it, sperm competition preserves the central purpose of male competition in his theory of sexual selection, with the reward to the victor being fertilization of the ovum. But the struggle occurs on the cellular level, among the sperm cells, with the female’s reproductive tract the field of battle. Male apes living in multimale social groups (such as chimps, bonobos, and humans) have larger testes, housed in an external scrotum, mature later than females, and produce larger volumes of ejaculate containing greater concentrations of sperm cells than primates in which females normally mate with only one male per cycle (such as gorillas, gibbons, and orangutans).

And, who knows? Perhaps Darwin would have recognized this process, if he’d been a bit less indoctrinated by Victorian notions of female sexuality. Sarah Hrdy contends that “it was Darwin’s presumption that females hold themselves in reserve for the best available male that left him so puzzled by sexual swellings.” Hrdy doesn’t buy Darwin’s “coy female” schtick for a minute: “Although appropriate for many animals, the appellation ‘coy’—which was to remain unchallenged dogma for the succeeding hundred years—did not then, and does not today, apply to the observed behavior of monkey and ape females at mid-cycle.”⁹

It’s possible Darwin was being a bit coy himself in his writings on the sexuality of human females. The poor guy had already insulted God, as most people—including his loving, pious wife—understood the concept. Even if he suspected something like sperm competition had played a role in human evolution, Darwin could hardly be expected to drag the angelic Victorian woman down from her pedestal. Bad enough that Darwinian theory depicts women evolving to prostitute themselves for meat, access to male wealth, and the rest of it. To have argued that ancestral females were shameless trollops motivated by erotic pleasure would have been too much.

Still, with characteristic awareness of just how much he

didn’t—and couldn’t—know, Darwin acknowledged, “As

these parts are more brightly coloured in one sex [female]

than in the other, and as they become more brilliant during the

season of love, I concluded that the colours had been gained

as a sexual attraction. I was well aware that I thus laid myself

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open to ridicule..”

Perhaps Darwin did understand that the bright sexual swellings of some female primates served to stoke male libido, which shouldn’t be necessary according his sexual selection theory. There is even evidence that Darwin may have had reason to ponder sperm competition in humans. In a letter from Bhutan, where he was gathering plants, Darwin’s old friend Joseph Hooker discussed the polyandrous humans he was encountering, where “a wife may have 10 husbands by law.”

Moderate body-size dimorphism isn’t the only anatomical suggestion of promiscuity in our species. The ratio of testicular volume to overall body mass can be used to read the degree of sperm competition in any given species. Jared

Diamond considers the theory of testis size to be “one of the

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triumphs of modern physical anthropology.” Like most great ideas, the theory of testis size is simple: species that copulate more often need larger testes, and species in which several males routinely copulate with one ovulating female need even bigger testes.

If a species has cojones grandes, you can bet that males have frequent ejaculations with females who sleep around. Where the females save it for Mr. Right, the males have smaller testes, relative to their overall body mass. The correlation of slutty females with big balled males appears to apply not only to humans and other primates, but to many mammals, as well as to birds, butterflies, reptiles, and fish.

In gorillas’ winner-take-all approach to mating, males compete to see who gets all the booty, as it were. So, although an adult silverback gorilla weighs in at around four hundred pounds, his penis is just over an inch long, at full mast, and his testicles are the size of kidney beans, though you’d have trouble finding them, as they’re safely tucked up inside his body. A one-hundred-pound bonobo has a penis three times as long as the gorilla’s and testicles the size of chicken eggs. The extra-large, AAA type (see chart on page 224). In bonobos, since everybody gets some sugar, the competition takes place on the level of the sperm cell, not at the level of the individual male. Still, although almost all bonobos are having sex, given the realities of biological reproduction, each baby bonobo still has only one biological father.