If we’re “above” nature, it’s only in the sense that a shaky-legged surfer is “above” the ocean. Even if we never slip, our inner nature can pull us under at any moment.


He looks for signs of youth, fertility, health, absence of previous sexual experience, and likelihood of future sexual fidelity. In other words, his assessment is skewed toward finding a fertile, healthy young mate with many childbearing years ahead and no current children to drain his resources.

She looks for signs of wealth (or at least prospects of future wealth), social status, physical health, and likelihood that he will stick around to protect and provide for their children. Her guy must be willing and able to provide materially for her and their children.


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).


In a nutshell, here’s the story we tell in the following pages: A few million years ago, our ancient ancestors shifted from a gorilla-like mating system where an alpha male fought to win and maintain a harem of females to one in which most males had sexual access to females.


Anthropologists have demonstrated time and again that immediate-return hunter-gatherer societies are nearly universal in their fierce egalitarianism. Sharing is not just encouraged; it’s mandatory. Hoarding or hiding food, for example, is considered deeply shameful, almost unforgivable behavior in these societies.

Foragers divide and distribute meat equitably, breastfeed one another’s babies, have little or no privacy from one another, and depend upon each other for survival.


The human male has testicles far larger than any monogamous primate would ever need, hanging vulnerably outside the body where cooler temperatures help preserve stand-by sperms for multiple ejaculations.


For nomadic foragers, personal property — anything needing to be carried — is kept to a minimum, for obvious reasons. There is little thought given to who owns the land, or the fish in the river, or the clouds in the sky.


Because of private property, for the first time in the history of our species, paternity became a crucial concern.


Where paternity is unimportant, men tend to be relatively unconcerned about women’s sexual fidelity.


If lamb chops are fine, what makes lamb brains horrible? A pig’s shoulder, haunch, and belly are damn fine eatin’, but the ears, snout, and feet are gross? How is lobster so different from grasshopper? Grind up those leftover pig parts, stuff them in an intestine, and you’ve got yourself respectable sausages or hot dogs.


Insects are richer in minerals and healthy fats than beef or pork.


Yet, the Europeans were convinced the Aborigines were starving to death. Why? Because they saw the native people resorting to last resorts — eating insects, grubs, and rats, critters that surely nobody would eat who wasn’t starving.


Our point? That something feels natural or unnatural doesn’t mean it is. Every one of the examples above is savored somewhere — by folks who would be disgusted by much of what you eat regularly.


We are not here concerned with hopes or fears, only with truth as far as our reason permits us to discover it.


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


Schopenhauer observed that “there are 80K prostitutes in London alone; and what are they if not sacrifices on the altar of monogamy?”


Flintstonization has 2 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 3 intellectual grandfathers: Hobbes, Rousseau, and Malthus.


It’s a waltz, with one assumption spinning into the next, circling round and round in “a spiral of comforting justification, proving how we came to be as we are.”


It’s important to understand that evolution is not a process of improvement. Natural selection simply asserts that species change as they adapt to ever-changing environment. One of the chronic mistakes made by would-be social Darwinists is to assume that evolution is a process by which human beings or societies become better. It is not.

Those organisms best able to survive in a challenging, shifting environment live to reproduce. As survivors, their genetic code likely contains information advantageous to their offspring in that particular environment. But the environment can change at any moment, thus neutralizing the advantage.


Today, self-proclaimed EP “realists” argue that it’s ancient human nature that lead us to wage war on our neighbors, deceive our spouse, and abuse our stepchildren. They argue that rape is an unfortunate, but largely successful reproductive strategy and that marriage amounts to a no-win struggle of mutually assured disappointment. Romantic love is reduced to a chemical reaction luring us into reproductive entanglements parental love keeps us from escaping. Theirs is an all-encompassing narrative claiming to explain it all by reducing every human interaction to the reptilian pursuit of self-interest.


Females, we’re told again and again, are the choosy, reserved sex. Men spend their energies trying to impress women — flaunting expensive watches, packaging themselves in shiny new sports cars, clawing their way to positions of fame, status, and power — all to convince coy females to part with their closely guarded sexual favors. For women, the narrative holds that sex is about the security — emotional and material — of the relationship, not the physical pleasure.


And yet, despite repeated assurances that women aren’t particularly sexual creatures, in cultures around the world men have gone to extraordinary lengths to control female libido: female genital mutilation, head-to-to-toe chadors, medieval witch burnings, Chasity belts, suffocating corsets, muttered insults about “insatiable” whores, pathologizing, paternalistic medical diagnoses of nymphomania or hysteria, the debilitating scorn heaped on any female who chooses to be generous with her sexuality… all parts of a worldwide campaign to keep the supposedly low-key female libido under control. Why the electrified high-security razor-wire fence to contain a kitty-cat?


In the common usage, promiscuity suggests immoral or amoral behavior, uncaring and unfeeling. But most of the people we’ll be describing are acting well within the bounds of what their society considers acceptable behavior. They’re not rebels, transgressors, or utopian idealists. Given that groups of foragers rarely number much over 100-150 people, each is likely to know every one of his or her partners deeply and intimately — probably to a much greater degree than a modern man or woman knows his or her casual lovers.


One can choose what to do, but not what to want.


What does the winning male suitor supposedly get for all his preening and showing off? Sex. Well, not just sex, but exclusive access to a particular woman. The standard model posits that sexual exclusivity is crucial because in evolutionary times this was a man’s only way of ensuring his paternity. According to EP, this is the grudging agreement at the heart of the human family. Men offer goods and services in exchange for exclusive, relatively consistent sexual access. Fisher called it The Sex Contract.

The sex contract is often explained in terms of economic game theory in which she or he who has the most offspring surviving to reproduce wins — because her or his ROI is highest. So, if a woman becomes pregnant by a guy who has no intention of helping her through pregnancy or guiding the child through the high-risk early years, she likely is squandering the time, energy, and risks of pregnancy.


Women are also predicted to compete in the marriage market, though they should compete over the males most likely to invest.

Conversely, if a guy invests all his time, energy, and resources in a woman who’s doing the nasty behind his back, he’s at risk of raising another man’s kids — a total loss if his sole purpose in life is getting his own genes into the future. And make no mistake: according to the cold logic of standard evolutionary theory, leaving a genetic legacy is our sole purpose in life.


The genius of Pretty Woman lies in making explicit what’s been implicit in hundreds of films and books. According to this theory, women have evolved to unthinkingly and unashamedly exchange erotic pleasure for access to a man’s wealth, protection, status, and other treasures likely to benefit her and her children.

Darwin says your mother’s a whore. Simple as that.


A man’s sexual attractiveness to women will be a function of traits that were correlated with high mate value in the natural environment… The crucial question is, What traits would have been correlated with high mate value? Three possible answers:

  • The willingness and ability to provide for a woman and her children.
  • The willingness and ability to protect.
  • The willingness and ability to engage in direct parenting activities.

We are built to be effective animals, not happy ones. (Of course, we’re designed to pursue happiness; and the attainment of Darwinian goals — sex, status, and so on — often bring happiness, at least for a while.) Still, the frequent absence of happiness is what keeps us pursuing it, and thus makes us productive.


Obviously, women don’t consciously think that sperm are cheap and eggs are expensive, but women in the past who failed to exercise acumen before consenting to sex were left in the evolutionary dust; our ancestral mothers used emotional wisdom to screen out losers.


Not only have males evolved to compete for scarce female eggs; females have evolved to compete for scarce male investment.


It’s not accident that the man who famously observed that power is the greatest aphrodisiac was not, by a long short, good-looking. Often, the men with the greatest access to resources and status lack the genetic wealth signified by physical attractiveness. What’s a girl to do?

Conventional theory suggests she’ll marry a nice, rich, predictable, sincerely guy likely to pay the mortgage, change the diapers, and take out the trash — but then cheat on him with wild, sexy, dangerous dudes, especially around the time she’s ovulating, so she’s more likely to have lover-boy’s baby.


According to the standard model, the worst-case scenario for a prehistoric woman in this evolutionary game would be to lose access to her man’s resources and support. If he limits himself to a meaningless sexual dalliance with another woman (in modern terms, preferably a woman of a lower social class or a prostitute — whom he would be unlikely to marry), this would be far less threatening to her standard of living and that of her children. However, if he were to fall in love with another woman and leave, the woman’s prospects (and those of her children) would plummet.

From the man’s perspective, the worst-case scenario would be to spend his time and resources raising another man’s children (and propelling someone else’s genes into the future at the expense of his own). If his partner were to have an emotional connection with another man, but no sex, this genetic catastrophe couldn’t happen.

The male’s mixed strategy would be to have a long-term mate, whose sexual behavior he could control. Meanwhile he should continue having casual (low-investment) sex with as many other women as possible, to increase his chances of fathering more children. This is how standard evolutionary theory posits that men evolved to be dirty, lying bastards. The evolved behavioral strategy for a man is to cheat on his pregnant wife while being insanely — even violently — jealous of her.


Conventional evolutionary theory assures us that all you scheming, gold-digging women reading this are evolved to trick a trusting yet boring guy into marrying you, only to then spray a bunch of perfume and run down to the local singles club to try to get pregnant by some unshaven Neanderthal as soon as hubby falls asleep on the couch. The male readers evolved to woo and marry some innocent young beauty with empty promises of undying love, fake Rolex prominent on your wrist, get her pregnant ASAP, then start “working late” with as many secretaries as you can manage.


The vast majority of other female mammals advertise when they are fertile, and are decidedly not interested in sex at other times. Concealed ovulation is said to be a significant human exception.


She suggests that concealed ovulation and extended receptivity in early hominids may have evolved not to reassure males, but to confuse them. Having noted the tendency of newly enthroned alpha male baboons to kill all the babies of the previous patriarch, she hypothesized that this aspect of female sexuality may have developed as a way of confusing paternity among various males.


If Thomas Hobbes had been offered the opportunity to design an animal that embodied his darkest convictions about human nature, he might have come up with something like a chimpanzee. Chimps are reported to be power-mad, jealous, quick to violence, devious, and aggressive. Murder, organized warfare between groups, rape, and infanticide are prominent in accounts of their behavior.


There are, however, some serious problems with turning to chimpanzee behavior to understand prehistoric human societies. While chimps are extremely hierarchical, groups of human foragers are vehemently egalitarian. Meat sharing is precisely the occasion when chimp hierarchy is most evident, yet a successful hunt triggers the leveling mechanisms most important to human foraging societies.


Several factors could have profoundly altered the chimps’ observed behavior. If we change things such as food supplies, population densities, and the possibilities for spontaneous group formation and dissolution… all hell breaks loose — not less for apes than for humans.


The chimpanzee resolves sexual issues with power; the bonobo resolves power issues with sex.


A caller faced with more than enough food will lose nothing by sharing it and may benefit later when another chimpanzee reciprocates.


Among bonobos, female “dominance” doesn’t result in the sort of male submission one might expect if it were simply an inversion of the male power structures found among chimps and baboons. The female bonobos use their power differently than male primates. Despite their submissive social role, male bonobos appear to be much better off than male chimps or baboons. “In view of their frequent sexual activity and low aggression, I find it hard to imagine that males of the species have a particularly stressful time.”


Bonobos engage in sex to ease tension, to stimulate sharing during meals, to reduce stress while traveling, and to reaffirm friendships during anxious reunions.


I sometimes try to imagine what would have happened if we’d known the bonobo first and chimpanzee only later or not at all. The discussion about human evolution might not revolve as much around violence, warfare, and male dominance, but rather around sexuality, empathy, caring, and cooperation.


Food sharing is highly associated with sexual activity in humans and bonobos, only moderately so in chimps.


Books like this one, concerning human nature, are beacons for trouble. On one hand, everybody’s an expert. Being human, we all have opinions about human nature. Such an understanding seems to require little more than a modicum of common sense and some attention to our own incessant cravings and aversion.


Human beings have been under cultivation longer than we’ve been cultivating anything else. Our cultures domesticate us for obscure purposes, nurturing and encouraging certain aspects of our behavior and tendencies while seeking to eliminate those that might be disruptive.


Strictly reproductive, once-in-a-blue-moon sex is more “animal” than human. In other words, an excessively horny monkey is acting “human,” while a man or woman uninterested in sex more than once or twice a year would be, strictly speak, “acting like an animal.”


For those of us born and raised in societies organized around the interlocking principles of individuality, personal space, and private property, it’s difficult to project our imaginations into those tightly woven societies where almost all space and property is communal, and identity is more collective than individual. A forager’s life is one of intense, constant interaction, interrelation, and interdependence.


Pregnancy is viewed as a matter of degree, not clearly distinguished from gestation. All sexually active women are a little pregnant. Over time, semen accumulates in the womb, a fetus is formed, further acts of intercourse follow, and additional semen causes the fetus to grow more.


Like mothers everywhere, a woman from these societies is eager to give her child every possible advantage in life. To this end, she’ll typically seek out sex with an assortment of men. She’ll solicit “contributions” from the best hunters, the best storytellers, the funniest, the kindest, the best-looking, the strongest, and so on — in the hopes her child will literally absorb the essence of each.


I told him that it was not honorable for a woman to love anyone else except her husband, and that this evil being among them, he himself was not sure that his son was his son. He replied, “You have no sense. You French people love only your own children; but we all love all the children of our tribe.”


Love is an ideal thing, marriage a real thing; a confusion of the real with the ideal never goes unpunished.


Sexual selection’s primary literature describes of extra-pair parentage as “cheating” on the pair bond; the male is said to be “cuckolded” offspring; offspring of extra-pair parentage are said to be “illegitimate” and females who do not participate in extra-pair copulations are said to be “faithful.” This judgmental terminology amounts to applying a contemporary definition of Western marriage to animals.


The sciences of human nature tend to validate the practices and preferences of whatever regime happens to be sponsoring them. In totalitarian regimes, dissidence is treated as a mental illness. In apartheid regimes, interracial contact is treated as unnatural. In free-market regimes, self-interest is treated as hardwired.


For many societies, virginity is so unimportant there isn’t even a word for the concept in their language.


Hostility toward this free expression of female sexual autonomy is not limited to narrow-minded anthropologists and 13th-century Italian explorers. Although the Mosuo have no history of trying to export their system or convincing anyone else of the superiority of their approach to love and sex, they have long suffered outside pressure to abandon their traditional beliefs, which outsiders seem to find threatening.


But rather than feel threatened, we’d recommend that our male readers ponder this: Societies in which women have lots of autonomy and authority tend to be decidedly male-friendly, relaxed, tolerant, and plenty sexy.


We who once compared ourselves to angels now see ourselves reflected in this lowly rodent.


Once marriage becomes common, jealousy will lead to the inculcation of female virtue; and this, being honored, will tend to spread to the unmarried females. How slowly it spreads to the male sex, we see at the present day.


It bears repeating that we are not attributing any particular nobility or, for that matter, ignobility to foragers. Some behaviors that seem normal to contemporary people (and which are therefore readily assumed to be universal) would quickly destroy many small-scale foraging societies, rendering them dysfunctional. Unrestrained self-interest, in particular, whether expressed as food-hoarding or excessive sexual possessiveness, is a direct threat to group cohesion and is therefore considered shameful and ridiculous.


But if it’s a question of genes, a man should be far less concerned about his wife having sex with his brothers — who share half of his genes — than with unrelated males.


“Evolution is a zero-sum game, with the victors winning at the expense of the losers.”

Far too often, the debate over the nature of human sexuality seems like a proxy war between antagonistic politico-economic philosophies. Defenders of the standard narrative see Cain’s gain as Abel’s loss, period. “That’s just how life is, kid,” they’ll tell you. “It’s human nature. Self-interest makes the world go round, pull yourself up by your bootstraps, it’s a dog-eat-dog world and always has been.”

This free-market vision of human mating hinges on the assumption that sexual monogamy is intrinsic to human nature. Absent monogamy (individual male “ownership” of female reproductive capacity), the I-win-you-lose dynamic collapses.


These researchers claim to have confirmed 2 important assumptions underlying the standard narrative: that men are universally worried about paternity certainty (hence, his mate’s sexual fidelity is his main concern), while women are universally concerned with access to men’s resources (so a woman will feel more threatened by any emotional intimacy that might inspire him to leave her for another woman).


Nothing is more prominent than love and sex in Western media.


Fear is certainly natural, and like any other kind of insecurity, jealousy is an expression of fear. But whether or not someone else’s sex life provokes fear depends on how sex is defined in a given society, relationship, and individual’s personality.

First-born children often feel jealous when a younger sibling is born. Wise parents make a special point of reassuring the child that she’ll always be special, that the baby doesn’t represent any kind of threat to her status, and that there’s plenty of love for everyone. Why is it so easy to believe that a mother’s love isn’t a zero-sum proposition, but that sexual love is a finite resource?


It is so very obvious that you can’t love more than one person? We seem to manage it with parental love, love of books, of food, of wine… why is erotic love the one exception that everybody instantly acknowledges without even thinking about it?


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.


The point is, ladies and gentlemen, that greed, for lack of a better word, is good. Greed is right, greed works. Greed clarifies, cuts through, and captures the essence of the evolutionary spirit. Greed, in all of its forms has marked the upward surge of mankind.


From this crystalline reasoning follows Malthus’s brutal conclusion: chronic overpopulation, desperation, and widespread starvation are intrinsic to human existence. Not a thing to be done about it. Helping the poor is like feeding London’s pigeons; they’ll just reproduce back to the brink of starvation anyway, so what’s the point? “The poverty and misery which prevail among the lower classes of society are absolutely irremediable.”


Wallace, who came up with the mechanism underlying natural selection independently of Darwin, experienced his own flash of insight while reading the same essay. Bernard Shaw smelled the Malthusian morbidity underlying natural selection, lamenting, “When its whole significance dawns on you, your heart sinks into a heap of sand within you.” Shaw lamented natural selection’s “hideous fatalism,” and complained of its “damnable reduction of beauty and intelligence, of strength and purpose, of honor and aspiration.”


Malthus assumed the suffering he saw around him reflected the eternal, inescapable condition of human and animal life.


Most foragers don’t start ovulating until their late teens, resulting in a shorter reproductive life.


Poverty is the invention of civilization.


In SV, millionaires don’t feel rich. You’re nobody here at $10M.


The world’s most primitive people have few possessions, but they are not poor. Poverty is not a certain small amount of goods, nor is it just a relation between means and ends; above all it is a relation between people. Poverty is a social status. As such it is the invention of civilization. Socrates made the same point 2K years ago: “He is richest who is content with least, for contentment is the wealth of nature.”


Those who proclaim that greed is simply part of human nature too often leave context unmentioned. Yes, greed is part of human nature. But so is shame. And so is generosity. When economists base their models on their fantasies of an “economic man” motivated only by self-interest, they forget community — the all-important web of meaning we spin around each other — the inescapable context within which anything truly human has taken place.


Hardin’s argument was a hit because (1) it features an A+B=C simplicity that appears to be inarguably correct; and (2) it is useful in justifying seemingly heartless decisions by entrenched powers.


These tragedies become inevitable only when the group size exceeds our species’ capacity for keeping track of one another, a point that’s come to be known as Dunbar’s number.


The same argument can be made concerning the tragic misunderstanding of human nature that underlies communism: community ownership doesn’t work in large-scale societies where people operate in anonymity. The bigger the society is, the less functional shame becomes. When the Berlin Wall came down, jubilant capitalists announced that the essential flaw of communism had been its failure to account for human nature. Well, yes and no. Marx’s fatal error was his failure to appreciate the importance of context. Human nature functions one way in the context of intimate, interdependent societies, but set loose in anonymity, we become a different creature. Neither beast is more nor less human.


Were we really born in the best possible time and place? Or is ours a random moment in infinity — just another among uncountable moments, each with its compensating pleasures and disappointments? We all have a psychological tendency to view our own experience as standard, to see our community as The People, to believe — perhaps subconsciously — that we are the chosen ones, God is on our side, and our team deserves to win.


It is a common mistake to assume that evolution is a process of improvement, that evolving organisms are progressing toward some final, perfected state. But they, and we, are not. An evolving society or organism simply adapts over the generations to changing conditions. While these modifications may be immediately beneficial, they are not really improvements because external conditions never stop shifting.


Just as Westerners’ behavior is understandable in relation to their assumption of shortage, so hunter-gatherers’ behavior is understandable in relation to their assumption of affluence.


Because food is found in the surrounding environment, no one can control another’s access to life’s necessities in hunter-gatherer society. In this context, egalitarianism is firmly rooted in the openness of resources, the simplicity of the tools of production, the lack of non-transportable property, and the liable structure of the band.


In a zero-sum context (like that of modern capitalist societies where we live among strangers), it makes sense, on some levels, for individuals to look out for themselves. But in other contexts human behavior is characterized by an equal instinct toward generosity and justice.


How would our appreciation of prehistory change if we saw that our journey began in leisure and plenty, only veering into misery, scarcity, and ruthless competition a hundred centuries ago?


Goodall’s impression of relative harmony was to change precisely when she and her students began giving the chimps hundreds of bananas every day, to entice them to hang around the camp so they could be observed more easily.


But once they learned that there would be a limited amount of easy food available in the same place each day, more and more chimps started arriving in aggressive, “noisy hordes” and “hanging around.” Soon after, Goodall and her students began witnessing the now-famous “warfare” between chimp groups.

Perhaps for the first time ever, the chimps had something worth fighting over: a concentrated, reliable, yet limited source of food. Suddenly, they lived in a zero-sum world.


Early agriculture’s stores of harvested grain and herds of placid livestock were like boxes of bananas in the jungle. There was now something worth fighting over: more. More land to cultivate. More women to increase population to work the land, raise armies to defend it, and help with the harvest. More slaves for the hard labor of planting, harvesting, and fighting. Failed crops in one area would lead desperate farmers to raid neighbors, who would retaliate, and so on, over and over.

Freedom (from war) is just another word for nothing to lose — or gain.


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: It depends.


When this factor is eliminated, we see that prehistoric humans who survived beyond childhood typically lived from 66-91 years, with higher levels of overall health and mobility than we find in most Western societies today.


The shift to agriculture was accelerated by the seemingly irrefutable belief that it’s better to take strangers’ land (killing them if necessary) than to allow one’s own children to die of starvation.


The less an individual slept, the more likely he or she was to come down with a cold. Those who slept less than 7 hours per night were 3 times as likely to get sick.

If you want to live long, sleep more and eat less.


Cortisol, the hormone your body releases when under stress, is the strongest immunosuppressant known. In other words, nothing weakens our defenses against disease quite like stress.


That would be encouraging news, indeed, which is what most audiences want to hear, after all. We all want to believe things are getting better, that our species is learning, growing, and prospering. Who refuses congratulations for having the good sense to be alive here and now?


Our species has an innate capacity for love and generosity at least equal to our taste for destruction, for peaceful cooperation as much as coordinated attack, for an open, relaxed sexuality as much as for jealous, passion-smothering possessiveness.


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. The biggest, baddest gorillas will pass genes for bigness and badness into the next generation, thus leading to ever bigger, badder male gorillas — until the increased size eventually runs into another factor limiting this growth.


It’s also an obstacle course, with the female’s body providing various types of hoops to jump through and moats to swim across to reach the egg — thus eliminating unworthy sperm. Some researchers argue that the competition is more like rugby, with various sperm forming “teams” with specialized blockers, runners, and so on. Sperm competition takes many forms.


As always, natural selection targets the relevant organs and systems for adaptation. Through the generations, male gorillas evolved impressive muscles for their reproductive structure, while their relatively unimportant genitals dwindled down to the bare minimum needed for uncontested fertilization.


Human being 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.


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 (though few think of it in quite these terms). Images and videos showing one woman with multiple males are far more popular on the Internet than those depicting one male with multiple females.


The act of swearing on one’s balls lives on in the word testify.


It bears repeating that the human penis is the longest and thickest of any primate’s — in both absolute and relative terms. And despite all the bad press they get, men last far longer in the saddle than bonobos (15s), chimps (7s), or gorillas (60s), clocking 4-7m, on average.


A scrotum is like a spare refrigerator in the garage just for beer. If you’ve got a spare beer fridge, you’re probably the type who expects a party to break out at any moment. You want to be prepared.


When it comes to sex, men may be trash-talking sprinters, but it’s the women who win all the marathons. After an orgasm, a woman may be anticipating a dozen more. A female body in motion tends to stay in motion. But men come and go. For them, the curtain falls quickly and the mind turns to unrelated matters.


There’s a good reason the sound of a woman enjoying sexual encounter entices a heterosexual man. Her “copulation call” is a potential invitation to come hither, thus provoking sperm competition.


Theories range from the belief that breasts serve as signaling devices announcing fertility and fat deposits sufficient to withstand the rigors of pregnancy and breastfeeding to “genital echo theory.”


Some women have orgasms sometimes because all men do every time.


Approximately 35% of the sperm are ejected within half an hour of intercourse and those that remain are anything but home free. The female’s body perceives sperm as antigens (foreign bodies) that are promptly attacked by anti-sperm leucocytes, which outnumber sperm 100:1. Only 1 in 14M ejaculated human sperm even reach the oviduct.


Sperm competition is best understood not as a sprint to the egg, but a race over hurdles. Aside from the anti-sperm leucocytes mentioned previously, anatomical and physiological obstacles are in the vagina, cervix, and on the surface of the ovum itself. The complexity of the human cervix suggests it evolved to filter the sperm of various males.


The war between the sexes is said to be built into our evolved sexuality: men want lots of no-strings lovers, while women want just a few partners, with as many strings as possible. If a man agree to be roped into a relationship, he’ll be hell-bent on making sure his mate isn’t risking his genetic investment by accepting deposits from other men.


One can, in effect, treat the sexes as if they were different species, the opposite sex being a resource relevant to producing maximum surviving offspring.


Faced with the mysteries of woman, Sigmund Freud, who seemed to have an answer for everything else, came up empty. “Despite my 30 years of research into the feminine soul, I have not yet been able to answer the great question that has never been answered: What does a woman want?”


Without testosterone, he said, “Everything I identified as being me was lost. My ambition, my interest in things, my sense of humor, the inflection of my voice. The introduction of testosterone returned everything.” Asked whether there had been an upside to being testosterone-free, he said, “There were things that I find offensive about my own personality that were disconnected then. And it was nice to be without them. I approached people with a humility that I had never displayed before.” But overall, he was glad to have it back, because, “When you have no testosterone, you have no desire.”


Before the hormone treatments, an attractive woman in the street would provoke an internal narrative: “She’s attractive. I’d like to meet her.” But after the injections, no more narrative. Any attractive quality in a woman was enough to “flood my mind with aggressive pornographic images, just one after another. Everything I looked at, everything I touched turned to sex. I felt like a monster a lot of the time. It made me understand men. It made me understand adolescent boys a lot.”


If we accept that our species is and always has been optimized for a highly sexual life and that adolescent boys are especially primed for action, why should we be surprised by the explosion of destructive frustration that result from the thwarting of this primal drive?


“At first, the sex was fantastic. I hadn’t felt so alive in years. I thought I was in love with Monica [the other woman]. When I was with her, it was like everything was stronger, you know? Food tasted better, colors were richer, I had so much more energy. I felt high all the time.”

When we asked if the sex he had with Monica was better than it had been with Helen, Phil paused for a moment. “Actually, now that I think about it, sex with Helen was much better — the best I’ve ever had, really — at the beginning, you know, those first few years. I mean, with Helen it was never just sex. We both knew we wanted to spend our lives together, so there was a depth and, well, a love and spiritual connection I’ve never had with anyone else.”


So what happened? “Over the years… you know how it is… the passion faded and our relationship changed. We became fiends… best friends, but still… siblings, almost.” His eyes tearing up, “It felt like a life-or-death situation. I wanted to feel alive again.”


What makes heterosexual men seek a constant stream of different women doing the same old thing is the Coolidge effect. Variety and change are the necessary spice of the sex life of the human male. But an intellectual understanding of this aspect of most men’s inner reality doesn’t make accepting it any easier for many women.


To avoid the genetic stagnation that would have dragged our ancestors into extinction long ago, males evolve a strong appetite for sexual novelty and a robust aversion to the overtly familiar.


Most of the men having affairs have told researcher they were actually quite happy in their marriages, while only one-third of women having affairs felt that way.


Even casual contact with novel, attractive women can have a tonic effect on men’s hormonal health. Even a brief chat with an attractive woman raised men’s testosterone levels by an average or 14%.


This loss of interest can frequently be reversed if the man has a younger lover — even if the lover is not as attractive or sexually skilled as the man’s wife. There seems to be no question but that the human male would be promiscuous in his choice of sexual partners throughout the whole of his life if there were not social restrictions.


We know that many female readers aren’t going to be happy reading this, and some will be enraged by it, but for most men, sexual monogamy leads inexorably to monotomy. It’s important to understand this process has nothing to do with the attractiveness of the man’s long-term partner or the depth and sincerity of his love for her. A man’s sexual desire for a woman to whom he is not married is largely the result of her not being his wife. Novelty itself is the attraction. The long-term partners of the sexiest Hollywood starlets are subject to the same psychosexual process.


Human males seem to be so constituted that they resist learning not to desire variety.


Need we supplement Symon’s thoughts with a list of specific examples of men (presidents, governors, senators, athletes, musicians) who have squandered family and fortune, power and prestige — all for an encounter with a woman whose principal attraction was her novelty? Need we remind female readers of the men in their past who seemed so smitten at first, but mysteriously stopped calling once the thrill of novelty had faded?


Phil thought he was in love. Of course he did. One of the few things that reliably revives a male’s sagging testosterone levels is a novel lover. So he felt all the things we associate with love: renewed vitality, a new depth and intensification — a giddy thrill at being alive.


How many families have been ripped apart because middle-aged men misinterpreted the surge of vitality and energy resulting from a novel sexual partner as love for a soul mate? And how many of these men then found themselves isolated, shamed, and devastated when the curse of Coolidge returned after a few months or years to reveal that the now-familiar partner was not, in fact, the true source of those feelings after all?


Once the transitory thrill passes, these men are left once again with the realities of what makes a relationship work over the long run: respect, admiration, convergent interests, good conversation, sense of humor, and so on. A marriage built upon sexual passion alone has as much chance of enduring as a house built on winter ice. Only by arriving at a more nuanced understanding of the human sexuality will we learn to make smarter decisions about our long-term commitments. But this understanding requires us to face some uncomfortable facts.


And if you’re a woman whose husband is “cheating,” your options are no better: pretend you don’t notice what’s going on, go out and have your own revenge affair (even if you don’t feel like it), or destroy your own family and marriage by calling in the lawyers. These are all losing scenarios.

Even the term we use to describe this betrayal of self and family, “cheating,” echoes the standard narrative of human sexuality in its implication that marriage is a game that one player can win at the expense of the other.


There is a cost for the society that insists on conformity to a particular range of heterosexual practices. We believe that cultures can be rationally designed. We can teach and reward and coerce. But in doing so we must also consider the price of each culture, measured in the time and energy required for training and enforcement and in the less tangible currency of human happiness that must be spent to circumvent our innate predispositions.


Yes, sex is essential, but it’s not something that must always be taken so seriously. Think of food, water, oxygen, shelter, and all the other elements of life crucial to survival and happiness but that don’t figure in our day-to-day thinking unless they become unavailable. A reasonable relaxation of moralistic social codes making sexual satisfaction more easily available would also make it less problematic.


Longevity, drug abuse, school performance and dropout rates, teen pregnancy, criminal behavior and incarceration… in all cases, the kids living with both parents drastically outperform the others.


Love is an ideal thing, marriage is a real thing. A confusion of the real with the ideal never goes unpunished.


The French are much more comfortable with the idea that their affair partner is just that — an affair partner. Understanding that love and sex are different things, the French feel less need to complain about their marriage to legitimize the affair in the first place. But Americans and British couples seemed to be reading from an entirely different script. An affair, even a one-night stand, means a marriage is over. I spoke to women who, on discovering that their husbands had cheated, immediately pack a bag and left, because “that’s what you do.” Not because that’s what they wanted to do — they just thought that was the rule. They didn’t even seem to realize there were other options.


But our concept of love and marriage has as its foundation not only the expectation of monogamy but the idea that where there’s love, monogamy should be easy and joyful.


Couples might find that the only route to preserving or rediscovering intensity reminiscent of their early days and nights requires confronting the open, uncertain sky together. They may mind themselves having their most meaningful, intimate conversations if they dare to talk about the true nature of their feelings.


But with trust, we can strive to accept even what we cannot understand. One of the most important hopes we have for this book is to provoke the sorts of conversations that make it a bit easier for couples to make their way across this difficult emotional terrain together, with a deeper, less judgmental understanding of the ancient roots of these inconvenient feelings and a more informed, mature approach to dealing with them.


An era can be considered over when its basic illusions have been exhausted.


From Iceland to Tierra del Fuego, people attributed the Sun’s constancy and power to his masculinity; the Moon’s changeability, unspeakable beauty, and monthly cycles were signs of her femininity.

To human eyes turned toward the sky 100K years ago, they appeared identical in size, as they do to our eyes today.