Sex at Dawn полностью

So the game’s still the same—getting one’s genes into the future—but the field of play is different. With harem-based polygynous systems like the gorilla’s, individual males fight it out before any sex takes place. In sperm competition, the cells fight in there so males don’t have to fight out here. Instead, males can relax around one another, allowing larger group sizes, enhancing cooperation, and avoiding disruption to the social dynamic. This helps explain why no primate living in multimale social groups is monogamous. It just wouldn’t work.

As always, natural selection targets the relevant organs and systems for adaptation. Through the generations, male gorillas evolved impressive muscles for their reproductive struggle, while their relatively unimportant genitals dwindled down to the bare minimum needed for uncontested fertilization. Conversely, male chimps, bonobos, and humans had less need for oversized muscles for fighting but evolved larger, more powerful testicles and, in the case of humans, a much more interesting penis.

We can almost hear some of our readers thinking, “But my testicles aren’t the size of chicken eggs!” No, they’re not. But we’re guessing they’re not tiny kidney beans tucked up inside your abdomen, either. Humans fall in the middle ground between gorillas and bonobos on the testicular volume/ body-mass scale. Those who argue that our species has been sexually monogamous for millions of years point out that human testicles are smaller than those of chimps and bonobos. Those who challenge the standard narrative (like us, for example) note that human testicular ratios are far beyond those of the polygynous gorilla or the monogamous gibbon.

So, is the human scrotum half-empty or half-full?

Small?

Both chimps and bonobos are far more promiscuous than we are. Our testicles reflect this: they are mere peanuts compared to our ape relatives’ coconuts.

FRANS DE WAAL¹

Medium?

Convincing vestiges of a sexual selective history in which females mated polyandrously can be found in the human male. Perhaps the clearest vestige is testis size. Men’s testes are substantially larger, relative to body size, than those of gorillas.

MARGO WILSON AND MARTIN DALY² Large?

Human beings are definitely at the big-ball end of the primate spectrum, more like chimpanzees than like gorillas ... suggesting that we have long been accustomed to competing via our sperm as well as our bodies.

DAVID BARASH AND JUDITH LIPTON³

As you can see, there is fundamental disagreement over the male package. What are we talking about here? Peanuts or walnuts? Ping-pong or bowling? Modern men’s testicles are smaller than those of chimps and bonobos, yet they put those of polygynous gorillas and monogamous gibbons to shame, tipping the scales at about half an ounce each (that’s about eighty carats, if you’re a jeweler). Thus both sides of this pivotal debate can claim evidence for their view simply by declaring that human testicles are relatively large or relatively small.

But measuring a testicle is not quite like getting a shoe size. The argument that modern men’s testicles would be as big as the chimps’ if we’d evolved in promiscuous groups is founded on a crucial and erroneous assumption: that human testicles haven’t changed in ten thousand years. When Stephen Jay Gould wrote, “There’s been no biological change in humans in 40,000 or 50,000 years,” he was relying on data that have been supplanted since he died in 2002. This still widely shared assumption grows out of the long-standing belief that evolution operates extremely slowly, requiring thousands of generations to make significant changes.

Sometimes it does. But sometimes it doesn’t. In The 10,000 Year Explosion, Gregory Cochran and Henry Harpending show that the human body is capable of very rapid evolutionary change. “Humans have changed significantly in body and mind over recorded history,” they write, citing resistance to malaria, blue eye color, and lactose tolerance as examples of accelerated evolutionary change since the advent of agriculture.