With and without love, a casual sexuality was the norm for our prehistoric ancestors.

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.

A great deal of research from primatology, anthropology, anatomy, and psychology points to the same fundamental conclusion: human beings and our hominid ancestors have spent almost all of the past few million years or so in small, intimate bands in which most adults had several sexual relationships at any given time. This approach to sexuality probably persisted until the rise of agriculture and private property no more than ten thousand years ago.

Clearly, the biggest loser (aside from slaves, perhaps) in the agricultural revolution was the human female, who went from occupying a central, respected role in foraging societies to becoming another possession for a man to earn and defend, along with his house, slaves, and livestock. Because of private property, for the first time in the history of our species, paternity became a crucial concern.

An essential first step in discerning the cultural from the human is what mythologist Joseph Campbell called detribalization. We have to recognize the various tribes we belong to and begin extricating ourselves from the unexamined assumptions each of them mistakes for the truth.

Sigmund Freud got it right when he observed that "civilization" is built largely on erotic energy that has been blocked, concentrated, accumulated, and redirected.

All too often, we inadvertently weave our own experiences into the fabric of prehistory. We call this widespread tendency to project contemporary cultural proclivities into the distant past "Flintstonization." Flintstonization has two parents: a lack of solid data and the psychological need to explain, justify, and celebrate one's own life and times. But for our purposes, Flintstonization has at least three intellectual grandfathers: Hobbes, Rousseau, and Malthus.

Modern man's seemingly instinctive impulse to control women's sexuality is not an intrinsic feature of human nature. It is a response to specific historical socioeconomic conditions--conditions very different from those in which our species evolved. This is key to understanding sexuality in the modern world.

No group-living nonhuman primate is monogamous, and adultery has been documented in every human culture studied--including those in which fornicators are routinely stoned to death. In light of all this bloody retribution, it's hard to see how monogamy comes "naturally" to our species. Why would so many risk their reputations, families, careers--even presidential legacies--for something that runs against human nature? Were monogamy an ancient, evolved trait characteristic of our species, as the standard narrative insists, these ubiquitous transgressions would be infrequent and such horrible enforcement unnecessary. No creature needs to be threatened with death to act in accord with its own nature.

Buss and other evolutionary psychologists who argue that some degree of jealousy is part of human nature may have a point, but they're overplaying their hand when they universalize their findings to everyone, everywhere, always. Human nature is made of highly reflective material. It is a mirror--admittedly marked by unalterable genetic scratches and cracks--but a mirror nonetheless. For most human beings, reality is pretty much what we're told it is. Like practically everything else, jealousy reflects social modification and can clearly be reduced to little more than a minor irritant if consensus deems it so.

According to E. O. Wilson, "all that we can surmise of humankind's genetic history argues for a more liberal sexual morality, in which sexual practices are to be regarded first as bonding devices and only second as a means for procreation." We couldn't have said it better. But if human sexuality developed primarily as a bonding mechanism in interdependent bands where paternity certainty was a nonissue, then the standard narrative of human sexual evolution is toast. The anachronistic presumption that women have always bartered their sexual favors to individual men in return for help with child care, food, protection, and the rest of it collapses upon contact with the many societies where women feel no need to negotiate such deals. Rather than a plausible explanation for how we got to be the way we are, the standard narrative is exposed as contemporary moralistic bias packaged to look like science and then projected upon the distant screen of prehistory, rationalizing the present while obscuring the past.

What if--thanks to the combined effects of very low population density, a highly omnivorous digestive system, our uniquely elevated social intelligence, institutionalized sharing of food, casually promiscuous sexuality leading to generalized child care, and group defense--human prehistory was in fact a time of relative peace and prosperity?

Without falling into dreamy visions of paradise, can we--dare we--consider the possibility that our ancestors lived in a world where for most people, on most days, there was enough for everyone? By now, everyone knows "there's no free lunch." But what would it mean if our species evolved in a world where every lunch was free? How would our appreciation of prehistory (and consequently, of ourselves) change if we saw that our journey began in leisure and plenty, only veering into misery, scarcity, and ruthless competition a hundred centuries ago?

Asking whether our species is naturally peaceful or warlike, generous or possessive, free-loving or jealous, is like asking whether H2O is naturally a solid, liquid, or gas. The only meaningful answer to such a question is: It depends. On a nearly empty planet, with food and shelter distributed widely, avoiding conflict would have been an easy, attractive option. Under the conditions typical of ancestral environments, human beings would have had much more to lose than to gain from warring against one another. The evidence--both physical and circumstantial--points to a human prehistory in which our ancestors made far more love than war.

A dispassionate review of the relevant science clearly demonstrates that the tens of thousands of years before the advent of agriculture, while certainly not a time of uninterrupted utopian bliss, was for the most part characterized by robust health, peace between individuals and groups, low levels of chronic stress and high levels of overall satisfaction for most of our ancestors.

Among mammals generally and particularly among primates, body-size dimorphism is correlated with male competition over mating. In winner-take-all mating systems where males compete with each other over infrequent mating opportunities, the larger, stronger males tend to win…and take all. On the other hand, in species with little struggle over females, there is less biological imperative for the males to evolve larger, stronger bodies, so they generally don't. That's why the sexually monogamous gibbons are virtually identical in size. Looking at our modest body-size dimorphism, it's a good bet that males haven't been fighting much over females in the past few million years. As mentioned above, men's bodies are from 10 to 20 percent bigger and heavier than women's on average, a ratio that appears to have held steady for at least several million years.

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).

"Love is an ideal thing, marriage a real thing," observed German philosopher Johann Wolfgang von Goethe. "A confusion of the real with the ideal never goes unpunished." Indeed. By insisting upon an ideal vision of marriage founded upon a lifetime of sexual fidelity to one person--a vision most of us eventually learn is highly unrealistic, we invite punishment upon ourselves, upon each other, and upon our children.

Despite centuries of religious and scientific propaganda, the basic illusions underpinning the supposed "naturalness" of the conventional nuclear family are clearly exhausted. This collapse has left many of us isolated and unfulfilled. Blind insistence and well-intentioned inquisitions have failed to turn the tide, and show no signs of future success. Rather than endless War Between the Sexes, or rigid adherence to a notion of the human family that was never true to begin with, we need to seek peace with the truths of human sexuality. Maybe this means improvising new familial configurations. Perhaps it will require more community assistance for single mothers and their children. Or maybe it just means we must learn to adjust our expectations concerning sexual fidelity. But this we know: vehement denial, inflexible religious or legislative dictate, and medieval stoning rituals in the desert have all proved powerless against our prehistoric predilections.