Sex at Dawn

• She will be sensitive to indications that he is considering leaving (vigilant toward signs of infidelity involving intimacy with other women that would threaten her access to his resources and protection)—while keeping an eye out (around ovulation, especially) for a quick fling with a man genetically superior to her husband.

• He will be sensitive to signs of her sexual infidelities (which would reduce his all-important paternity certainty)—while taking advantage of short-term sexual opportunities with other women (as his sperm are easily produced and plentiful).

Researchers claim to have confirmed these basic patterns in studies conducted around the world over several decades. Their results seem to support the standard narrative of human sexual evolution, which appears to make a lot of sense. But they don’t, and it doesn’t.

While we don’t dispute that these patterns play out in many parts of the modern world, we don’t see them as elements of human nature so much as adaptations to social conditions—many of which were introduced with the advent of agriculture no more than ten thousand years ago. These behaviors and predilections are not biologically programmed traits of our species; they are evidence of the human brain’s flexibility and the creative potential of community.

To take just one example, we argue that women’s seemingly consistent preference for men with access to wealth is not a result of innate evolutionary programming, as the standard model asserts, but simply a behavioral adaptation to a world in which men control a disproportionate share of the world’s resources. As we’ll explore in detail, before the advent of agriculture a hundred centuries ago, women typically had as much access to food, protection, and social support as did men. We’ll see that upheavals in human societies resulting from the shift to settled living in agricultural communities brought radical changes to women’s ability to survive. Suddenly, women lived in a world where they had to barter their reproductive capacity for access to the resources and protection they needed to survive. But these conditions are very different from those in which our species had been evolving previously.

It’s important to keep in mind that when viewed against the full scale of our species’ existence, ten thousand years is but a brief moment. Even if we ignore the roughly two million years since the emergence of our Homo lineage, in which our direct ancestors lived in small foraging social groups, anatomically modern humans are estimated to have existed as long as 200,000 years. With the earliest evidence of agriculture dating to about 8000 BCE, the amount of time our species has spent living in settled agricultural societies represents just 5 percent of our collective experience, at most. As recently as a few hundred years ago, most of the planet was still occupied by foragers.

So in order to trace the deepest roots of human sexuality, it’s vital to look beneath the thin crust of recent human history. Until agriculture, human beings evolved in societies organized around an insistence on sharing just about everything. But all this sharing doesn’t make anyone a noble savage. These pre-agricultural societies were no nobler than you are when you pay your taxes or insurance premiums. Universal, culturally imposed sharing was simply the most effective way for our highly social species to minimize risk. Sharing and self-interest, as we shall see, are not mutually exclusive. Indeed, what many anthropologists call fierce egalitarianism was the predominant pattern of social organization around the world for many millennia before the advent of agriculture.

But human societies changed in radical ways once they started farming and raising domesticated animals. They organized themselves around hierarchical political structures, private property, densely populated settlements, a radical shift in the status of women, and other social configurations that together represent an enigmatic disaster for our species: human population growth mushroomed as quality of life plummeted. The shift to agriculture, wrote author Jared Diamond, is a “catastrophe from which we have never recovered.”⁶

Several types of evidence suggest our pre-agricultural (prehistoric) ancestors lived in groups where most mature individuals would have had several ongoing sexual relationships at any given time. Though often casual, these relationships were not random or meaningless. Quite the opposite: they reinforced crucial social ties holding these highly interdependent communities together.⁷