Man and Woman, Part II: The Sexual Deal: A Story Of Civilization

Homo sapiens. Types: male and female. Age: about 400,000, with known ancestors of 3,500,000. Distribution: virtually entire surface of planet Earth. Societies: agricultural and industrial, with a few primitive hunter-gatherers. Mode of reproduction: sexual. Nearest living relative: chimpanzee. Characteristics: intelligent, dominant, highly sexed. Question: Why?

A visitor from another galaxy who materialized here with limitless funds would have a hard time explaining to her distant bosses why human men and women dominate the earth. Where would she begin? We're not the biggest species, after all---the blue whale is 1000 times larger. We're not the longest-living---a bristlecone pine can outlast 150 human generations. We're not anything like as numerous as birds. And we don't reproduce particularly fast---other species can do in 20 minutes what takes us nine months. Only two things, in fact, combine to make us in any way special. The ratio between our brain weight and our body mass is the highest on earth; and we are by far the sexiest creatures on the planet.

Our closest cousins are chimpanzees, with whom we share 98.5 percent of our genes. And scientists agree that a cross between a chimp and a human being is entirely possible; the Chinese are said to have tried it before they were rudely interrupted by the Cultural Revolution. How they went about it, before the days of test-tube babies, no one knows. And what the sexual behavior of the result might have been fairly boggles the mind. For a chimp's sex life is a pretty sorry business compared with ours. Chimp males, it is true, may be said to have an advantage

over us human males---their testicles are three times larger than ours and they produce huge amounts of sperm. But that's only because they have to compete with one another all the time. Male chimps have sex only when an individual female comes into heat---after two or three years, if she's pregnant or nursing an infant. They usually have to queue up for it. And when the time comes to do what they've been waiting for, the whole thing is over in seven seconds.

By contrast, we humans have fun. And we look as if we were designed for it: All the necessary equipment is carried up front, permanently on display. We're hairless, for maximum visibility and sensitivity. We tend to copulate face to face, to have as much personal contact as possible---though there are as many variations on this theme as there is human ingenuity. And we do it more often. Human beings aren't hidebound by breeding seasons and breeding cycles, as are chimpanzees and the rest of nature. We have sex not only for reproduction but for pleasure as well.

That's something our intrepid intergalactic anthropologist would notice very quickly. And she'd notice, as she scanned the species, two other things that humans characteristically do that seem to be related to all this sexual delight. First, we're basically monogamous, unlike almost all other primates except the gibbon and the siamang. And, second, we have a division of labor between the sexes; there seems to be an agreement about who does what.

Of a total of 224 societies listed in George Murdock's Ethnographic Atlas, 158 list cooking as a strictly female activity and only five say it's exclusively male. Hunting is done by males in 166 societies out of 179 and never exclusively by females. And it's the same story with other jobs about the house and hut. Males are almost always responsible for lumbering, metalworking, fishing and the making of musical instruments. And females, by and large, take over weaving, clothes making and the preparation of drinks and narcotics. This sort of division of labor is unique in nature, except among birds.

Having understood this much, our visitor from outer space would want to try to put two and two together for her report. Large brains, pleasure, monogamy, sexiness and division of labor: Could those explain why human beings have come to dominate the planet Earth? Could sex and sexuality, after all, be at the heart of it? And if she wanted to answer those questions, she'd have to go a long way back in history: past our first settlements a mere 15,000 years ago, past our first tools and past our beginnings---backward in evolutionary time and out into nature, to the species that have been around for millions and even billions of years, long before our arrival. And there she'd have to ask two further questions that are basic to who we are, questions that the population of her galaxy---all female---are desperate to have answered. Why does sex exist? And why do males exist?

Sex may be fun, but it isn't necessary. Consider, for example, the many species of lizard biologist David Crews keeps in his laboratory at Harvard. Three of them are particularly interesting; for when a female of one of those species is about to ovulate, she is mounted by another lizard and what looks a lot like sex takes place. There is much biting, lashing of tails and juxtaposition of sexual organs.

It is not, however, sex---at least not in the way we usually think of it. Because all lizards of those three species are female. Like at least 24 other species of reptiles and like the people of our imaginary visitor's galaxy, they specialize in virgin birth---parthenogenesis---and have single-parent families of female offspring exactly like themselves. The sex they have has a function. It makes them lay more eggs more often. But it has nothing to do with fertilization. They reproduce on their own, without any need for help from males. They have done away with them and will never need them again, even if Crews manages to make some males by injecting their eggs with male hormones.

Pity, then, the poor male lizard. And take warning. For the same thing could conceivably happen in humans. Some biologists believe that were the gene for parthenogenesis to appear in any longlived species that inhabits a stable environment, as we do, it would take over and eventually consign both males and sex to oblivion. We would become like dandelions, bananas, pineapples, Washington navel oranges and the occasional turkey---as well as like our female observer and Crews's lizards. We would be born without benefit of sex and in our case, too, all female.

Some feminists would argue that the world would be better off that way; and if you look at males in most of nature, you'll probably agree. For males in nature are by and large rather useless creatures, good only for one thing. They contribute far less to the reproduction of their species than females do. They're usually smaller than females (the largest creature on earth is, in fact, a female blue whale). They almost never help out with the kids. They die young (only human eunuchs live as long as human females) and when they're alive, they behave in extremely foolish ways.

They fight among themselves---male mites battle to the death---for the privilege of a mating. They also expose themselves to predators when they strut their stuff---for example, only male fireflies take to the air for a flashing session; the female is safe in the underbrush. Males commit themselves to hopelessly elaborate evolutionary strategies, such as the swagger matches of reindeer and their massive investment in useless antlers. And very often, males have no clear idea of who or what to date. A male fly will try it with a raisin; a male butterfly, with a falling leaf. And male frogs and toads will optimistically attach themselves to a rock or a stone or a passing boot.

Being a male, in other words, is in most species a difficult, dangerous, nasty and hit-or-miss business. Nature has designed males to do anything to achieve reproductive success; that's all nature is interested in. And the price for that success is sometimes very high. Male marsupial shrews, for instance, get a fatal dose of stereoid hormones when they copulate. Male Neotropical frogs virtually starve themselves to death as they wait weeks or even months on the back of a female for her eggs to mature. And male angler fish, just to perform their reproductive duty, commit an awesome form of suicide. They latch on with pincers to the body of a female, become a part of her skin surface and circulatory system, lose their eyes and fins in the process and end up becoming about a hundredth of her size. All that for one tiny moment of glory, when the female releases her eggs into the water to be fertilized.

It's no wonder, then, given the rotten time most males seem to have of it, that those few males that have the option--- some coral-reef fish, for instance---actually fight with each other for the right to become female.

The majority of males don't have that option. Like humans, they're locked into whatever evolution gave them---from the 18 different patterns in the courtship dance of the American grasshopper to the bull elephant's unwieldy 60-pound penis to whatever lurks in the collective psyche at a big-city singles bar. They're locked into the evolved expression of their male sexuality. All of which may come as something of a surprise to human males who think of themselves as varied and sophisticated, newly arrived and in the game only for pleasure.

But we, too, evolved a long time ago. And we, too, are subject to this basic law of nature: that the only way a male can reproduce himself and pass on his genes to the next generation is to find a mate, compete for her and do whatever she thinks necessary. If males, including human males, don't do this---if they don't make it through the struggle and don't come up to snuff with the female---then they're on a one-way ticket to reproductive oblivion. And whatever genes they carried that produced their particular disability---their choice of pleasure over conception, their urge to stay home and not bother, their weakness, their muffing of the courtship dance or their lack of attractive pizzazz---will disappear from the population.

Only the genes for whatever it took to survive and reproduce with a female will remain: the biggest, the bravest, the most persistent, the most punctual and the most colorfully decorated. That is the way the world turns, for males. With the female in charge of the manufacturing end of reproduction, males are only in the service business and they must jump to the female's tune.

Irven DeVore, a Harvard anthropologist, is certain about this. "Males," he says unequivocally, "are a vast breeding experiment run by females."

The question is, though: What on earth for? It's clear that the existence of sex is of vital importance for males in nature; without it, they wouldn't be around. But what's in it for females? Sexual reproduction, after all, takes time and energy (in flatworms, which can reproduce with or without sex, it takes 15 percent more time and 25 percent more energy). And it also presents a female with several serious problems.

First, she has to find and risk having close to her a potentially dangerous partner. Second, she has to find a way of making sure she's mating with an individual of the right species. And, third, she has to take a gamble on whether or not the male's sperm will enable her to produce fit offspring. Some of the winnowing out of males has already been done, of course, by the rigors of the environment and by male-male competition. But a female's eggs are still more expensive to produce than a male's sperm---in birds, the egg can represent as much as a quarter of a female's body weight: and in humans, men can produce in half a second more sperm (the smallest cells in their bodies) than a woman can produce eggs in her whole lifetime.

A female, then, is forced to be more choosy than a male. In humans, a moment's indiscretion with the wrong sperm can cost a woman an egg that would have been better invested elsewhere, not to mention nine months of pregnancy and a lot of bringing up baby.

All that, you would think, would encourage the female of the species to find some other means of reproduction. And there is an even stronger and more important reason why she should. It is that, quite apart from all the inconvenience and fuss, sex---evolutionarily speaking, (continued on page 186) Man and Woman (continued from page 98) from the point of view of her genes---is a bad option for her. For if she has survived up to this point, after all, she has very good genes; they've traveled down to her, from the year dot, only through reproductively successful organisms.

So why should she want to break up a winning combination? Why should she want to throw away half her genes, shuffle them up in the process and take another shuffled half from another individual, usually a perfect stranger? Why should she give up the reproductive edge her genes have already got? And why should she waste time and resources producing males?

"It's no use saying, 'Well, it's for the good of the species,' " says Martin Daly. Daly is a Darwinian psychologist, now at McMaster University in Canada, who has long been interested in why he exists.

"The female doesn't know anything about species and she doesn't do anything at the beck and call of evolutionary theorists," he says. "No, there has to be something in it for her. That's all she's interested in, herself and her offspring; or, put another way, that's all her genes are interested in, themselves and their continuation. Selection takes place at the level of the individual. And that's where we have to look for whatever advantage it is that sex brings. By choosing sex, you see---as George Williams of Stanford has pointed out---the female has on the face of it put her genes at a 50 percent disadvantage; only half of them are transmitted. So we have to find a corresponding 50 percent advantage that sex must offer. What can that advantage be? It has to be something enormous. She's at a 50 percent disadvantage, remember, and we know that the genes for even a one percent disadvantage will very quickly disappear from any population, other things being equal."

Daly and his wife, Margo Wilson, a research associate at McMaster, recently wrote a book called Sex, Evolution and Behavior. In it. they come to no firm conclusions about the origins of sex, but they do suggest what it's good for---adaptation in the face of bad times.

"Look, all we've got to go on is what's in nature," says Daly, a dry, funny man in his late 30s who delights in bringing us humans down to size by calling us "H. saps." "And, luckily, nature has given us an unbelievable-variety of life, from bacteria all the way to H. saps. Bacteria aren't much use, because they don't use sex very much, even though they're about 6000 times older than we are and the most numerous and most successful organisms on earth. And H. saps aren't much use, because they're already committed to this thing we're trying to explain.

"But between them are a number of species that are sometimes sexual and sometimes asexual. And they seem to have one overriding thing in common. As long as the going is good, as long as there's not too much competition, they put all their money on the asexual option. They produce females. But if there's overcrowding or they're faced with an imminent collapse, they opt for sex. They produce males."

Just like human beings in wartime, in other words, who take sex wherever they can because they may not survive, so a whole host of creatures switch to it when their way of life is threatened. For females in nature, hard times are responsible for the fact of sex, as well as for the act of sex. Males become necessary. In species where there is an option of being either male or female, males are almost always found where the environment makes survival tough going.

So far, so good, O people of the galaxy. But why is there so much sex on this planet? Birds do it. Bees do it---actually, only some bees do it. Even uneducated little fleas do it. We do it. And we and they do it all the time. Somewhere along the line, a few billion years ago. there must have been a switch to sex and it must have stuck. Why?

Put it this way. Males are a pretty good idea when it comes to females' competing against an uncertain future. Males are usually smaller, they mature faster and their sex cells are cheaper to produce. So, from a female's point of view, males are an efficient way of storing their genes when resources are scarce. And they're also a good way of making sure that copies of at least some of those precious genes are passed on to the next generation.

Males, after all, produce enormous numbers of sex cells---with the female parent's genes inside them. And so, if they survive to maturity, there's a good chance that at least one of those little gene loads, and maybe more, will find a home in an organism that has retained the option of being female. That is a much better prospect for her genes than simply continuing to make 100 percent copies of themselves; she's not doing well in the environment she's got and they're not going to do any better. A much better plan, then, is to make males, have sex, mix up genes and start again. For the next generation will all be different from one another, and there's a chance that some of them will have what it takes to cope and carry on.

But that still doesn't explain why females took up sex full time. rather than keep it for an occasional option. We, for example, don't seem to have been faced with a continuous chain of emergencies throughout our history. Nor does any other sexual species that we know of. So why don't human females simply make clones of themselves and keep men in reserve, in case of disaster?

For an answer, we have to go back in time, back to how the idea occurred in the first place. The search takes us to the primordial ooze, by way of a tall question mark of an Englishman named William Hamilton. A biologist at the University of Michigan at Ann Arbor, Hamilton believes that the only way a sexual population can beat out an asexual one is for it to be permanently under threat from outside---from parasites.

"Men and women," Hamilton says carefully amid the clutter of his university office, "are descended from the first multicellular organisms. And I've always been puzzled by how those organisms could survive. They're at a distinct disadvantage against their smaller enemies. They're more complicated. so they grow and reproduce much more slowly, which makes them vulnerable, evolutionarily speaking. Because when one organism is trying to figure out a way into another, and the other is trying to figure out a way to keep it out. evolution favors the one that breeds quicker. Mutations will give it better ideas faster, and it will win. Unless, and only unless, the bigger organism can figure out a new genetic trick to level the odds.

"And I think that trick was sex," Hamilton continues, "the mixing of genes between two of the organisms to make new arrangements---new passwords, perhaps---to keep the parasites out. That would now give the multicellular an edge in this evolutionary game of catch-up, but only a small edge. And so, as it gets larger, all the way down to us, sex would constantly be selected for. Sex would have to go on.

"All right. That's maybe why there is sex. But why are there sexes? Exchanging genes, after all, doesn't necessarily mean that there should be any difference between the two exchangers. When bacteria use sex, for example, there's no difference that can be found.

"Well, here I think science does have an answer. When the evolutionary step toward sex is taken by a multicellular organism, cells specifically for sex will tend to be produced. But there's an inherent instability that acts against there always being of the same size. And the pressures of competition will begin. Those pressures will favor slightly larger sex cells than usual. And those, in turn, will make for cheats, smaller sex cells than usual, produced in greater numbers to compete for the bigger ones. From then on, the pattern becomes clearer and clearer. The small sex cells become more and more competitive---they become highly mobile, they learn to swim---while the large sex cells become immobile and fixed. The cheats become sperm and the cells for which they compete become eggs. And that's what we end up with. Sperm and eggs. Small investors and large investors. Cheats and straight shooters. Males and females."

This may not seem very romantic, but from it all blessings flow. For now you has sex. Now you has males. And now you has all the incredible, teeming variety of sex in nature: male mites that fertilize their sisters while still inside their mother, and so die before they are born; the female scorpion fly that insists on a titbit from her prospective lovers, and her transvestite brother---in drag---that tries to con poor unsuspecting males out of their nuptial gifts; the ingenuity and elaborate pleasures of human beings. Not to forget what British researcher Tim Clutton-Brock has called the "sneaky fucker strategy" in red-deer stags. Among those animals, the dominant males spend a great deal of time showing off their wares to one another. Less dominant males will have none of that; instead, while the big boys are quarreling, they sneak around back and get it on with the females. In nature, it doesn't matter how you play the game, as long as you win.

Reproductive success is the name of this game, and the table is almost always run by the female. With a much bigger investment now at stake, it's up to her to be choosy about what genes she accepts into her eggs. That's why the delay of courtship suits her purposes well. Males, characteristically, have a different strategy. Their sperm costs little and they can have multiple matings. So it is in their interests to spread their genes across as many females as possible---to go all the way on the first date and then move on.

That would be fine, if there were always more females than males in the population. But genetic rules ordain that there will always be, roughly speaking, equal numbers. Which means that males will have to compete with one another; some can be big winners in the game and others will have to be losers. If a king can take 3333 wives, after all, as he could by law in one African nation, then there'll be roughly 3332 other men left without any. The same is true in nature.

On the face of it, this system---this rat-race polygamy---may look as if it works to the disadvantage of the female. But, remember, she's interested only in the successful reproduction of her genes. So the system actually works hugely to her advantage. Because if the males spend their time competing---sorting out the toughest, most ambitious and most resilient genes from the weaker and less capable---it makes her job of selection that much easier. She wants resources, after all, sometimes just the resources of good genes, and so fair play is the last thing on her mind.

In many species, in fact, perhaps including our own, females actively encourage all the Sturm und Drang. In sand bees, females remain resolutely below the surface, so that a male will have to dig down to them while fighting off other males. In coyotes, females will deliberately delay mating until a large number of males have arrived. And in the Uganda kob, the handsomest of the African antelopes, females stroll through the stamping ground, where the males are fighting and jockeying with one another; the females are inspecting the goods, as if in a sexual meat market. (Think again of the singles bar, gentlemen, and reconsider who's really in charge.)

If you think this is pretty antisocial behavior on the part of all concerned, you're right. "Sex," as E. O. Wilson, one of the founders of sociobiology, wrote, "is an antisocial force in evolution." In a sense, it is also the most deadly for males. For in all of this, males, even human males, die young: not because they kill each other off, and not because they are forced to become conspicuous, though both help, but because selection is interested only in their reproductive ability and not in any genes that might help stave off their death after reproductive age. The males in most species aren't involved, as we've said, in bringing up the children. So once they've done their duty to Mother Nature, they are expendable.

While they're alive, of course, they have one other task demanded of them by the female: to court her. Courtship in nature takes many forms, and sometimes it works to protect males, who can find out in the process whether or not a female has already been inseminated (a long engagement will always tell).

But, for the most part, courtship is no more than a job-application system designed by the female employer. First, is the applicant of the right species? ("Are you my type?") Second, can he perform the foreplay necessary to bring the female to ovulation? ("Can you make nice?") Third, can he do anything else to demonstrate that he has good genes? ("What's so special about you?") (Nature---and human society---is full of demonstrations of resources, chases, forced journeys and other tests imposed on the male by the female.) Fourth, and most interestingly, perhaps, is the applicant aesthetically pleasing? ("What's your wardrobe like?") Males in nature are almost always more exotically colored and elaborately ornamented than females. And it's clear that those features have been selected for by females, other things being equal, for their own enjoyment. Males are a vast breeding experiment run by females. And females have not only designed them, they have also, by being in charge of reproduction, ordered the kinds of society in which they'll live.

Take the king of beasts, for example. No, take the queen of beasts; lionesses run faster and do most of the hunting. A pride of lions consists of a number of lionesses, usually interrelated, and two larger males, unrelated, who are needed for protection against other lions that might invade the pride and kill the females' cubs. One lion isn't enough for this job. How, though, to avoid competition between those two males? How to make them work together?

Simple. Whenever the females come into heat, they do so all at the same time. From then on, for two or three days, they all require copulation every 15 or so minutes. And by the time the mating session is over, the males are too exhausted to know which is whose, what is why or which end is up. Result? Peace at home and protection guaranteed. The females get what they want.

They always do. Selfish females never allow equally selfish males a say in the way their society operates unless the environment demands it, or unless they have successfully bred males to do something more useful to themselves and their offspring than just provide sperm. Male and female strategies will always make for male-male competition, polygamy and disposable, interchangeable males, unless males can be encouraged into a line of work that has a direct effect on the females' reproductive success. What is that line of work in primates, the creatures closest to us? The protection racket. What is that line of work in man? Male parenting.

The quality and intensity of paternal care that a male human gives to his offspring sets him off from all the other primates. It has also been his salvation, for male parenting rewrites the rules of the relationship between males and females. It equalizes the unequal struggle between the sexes. And it is almost certainly the one thing that will save human sex and human males from the dark waters of forgetfulness, if the genes for parthenogenesis---virgin birth---ever reappear in the population of Daly's H. saps. Since the days males first came into existence---prodded by parasites, if Hamilton is right---male parenting in return for female-male monogamy has been the best deal they've ever made.

To understand why, we have to look where Daly told us we should look, for an advantage at the individual's level. What's in it for a man, or, rather, for his genes? For, obviously, they now face a giant disability: What with feeding the wife and taking care of the kids, they can't spread themselves all over the place as they once could, given a certain amount of perseverance and luck. So what's the new benefit they receive?

Well, in the old days of competition, "sneaky fuckers" and multiple mating---which may well survive within us in some form---who knew whose sperm was getting through to whose egg, to deliver up the genetic goods? At least now the male, by committing himself to a female, can have some confidence that her offspring are also his, because she'll want what he provides enough not to screw around. This means that competition with other males now becomes counterproductive: A male who leaves home for a fling can't ever be sure that there isn't another male knocking at his door. It means that a male will live slightly longer, since nature now has an interest in his survival through child-care years. And it means that a male can now give the 50 percent of his genes that are in his children a far better chance of surviving to pass them on. His children can be carefully prepared for the environment in which they will find themselves. They can stay young and dependent longer.

That, of course, makes male parenting the best show in town as far as the female is concerned. Consequently, it's in her interests to promote it with the full force of her genes, because now she can get back the advantage she lost when she was forced to abandon asexual reproduction and take up sex. She gives up her independence, it's true. She can't make a date on a whim with the best new genes available. And she has to put up with the burden of her male mate's needs. The advantages, however, far outweigh those costs. For, with male assistance and resources, she can perhaps double the number of her offspring and the number of genes she personally can contribute to the next generation. And, like the male, she can make sure they get off to the best possible start in life.

Sexual access and some guarantee of paternity, in exchange for more resources than the female can command herself, all for the good of the children; that is the basic trade-off involved in monogamy. Ninety percent of birds have made it. Gibbons and siamangs have made it. And Owen Lovejoy, professor of anthropology at Kent State University, believes that in our species, not only was that trade-off made millions of years ago by our ancestors, it was also responsible for human civilization.

"Anthropologists have always argued," Lovejoy says, "that it is the use of tools that separates man from all the other primates. Tools, big brain, language and upright posture; they all somehow come together in one evolutionary bundle. And I think that's nonsense. For me, there's only one thing that can explain all the things we want to have explained: walking on two legs, intelligence, culture, dominance. And that's the mating and parent-care pattern that evolved in our species---the division of labor for greater reproductive success. Monogamy. We'll never find it in fossil form, of course, but I believe it is absolutely fundamental to human evolution. Right at the core."

Lovejoy is a bearded, tough-minded man in his 30s, another of a new generation of scientists bucking old assumptions and facing up to old unanswered questions. He holds positions in human anatomy and orthopedic surgery, as well as in anthropology. He has worked in close association with Donald Johanson, the discoverer, in Ethiopia, of Lucy, the skeleton of the earliest-known upright-walking hominid. And the day we meet him, he has been confirming for the sheriff's department the identity of yet another skeleton, a human one he calls Joey, the headless, handless victim of a recent gangland slaying in nearby Ashtabula County.

We talk for several hours in an offcampus restaurant, a favorite haunt of Lovejoy's. "Look," he says almost as soon as he sits down, "I'm an early type. And we early types aren't interested in what's gone on in the past 400,000 or 500,000 years. We're interested in the long haul of human evolution. And that's what makes Lucy so fascinating. Because she presents us with a problem. First, she's three and a half million years old---older than any tools or human culture we know of. Second, she's not very smart---she has a primitive skull much like an ape's. But third---despite all that---she had a body that was fully upright and she could walk in exactly the same way you walked in here. Now, why would she need to do that? To hunt? To avoid predators? No. She'd be much better off on all fours: Upright humans can do only about 40 percent of the speed of the patas monkey; they can only just outrun a fast snake; and their walking speed's about the same as a chicken's. Hardly what you'd want in the dangerous open grasslands hominids are supposed to have evolved in after they left the forest. To feed? No. The teeth of Lucy's species show they were generalist eaters. And you don't need upright posture in the savanna on that diet. Why, then?"

Lovejoy leans on the question. "The answer is simple, it seems to me. Lucy's species---Australopithecus afarensis, our earliest known ancestors---were food carriers. And long before they moved out into the open, they carried food to one another.

"No big deal, you might think. Very big deal. Because, to exist, an adaptation as big as this has got to show a reproductive advantage. The enormous anatomical change necessary for this behavior must have to do with survival and reproductive success. It's not just early men suddenly deciding to be nice to one another for no reason. Where would be the incentive? Well, there obviously was an incentive. And I propose that it was the result of a new deal between males and females and a new way of bringing up offspring---the whole thing cemented by sex.

"The best way to see what I mean," Lovejoy continues, "is to look at chimps, our nearest living relative. Chimps mature very slowly, just like humans. They have biggish brains, and they use rudimentary tools and weapons and they walk upright once in a while. But the one thing they don't do is forage for one another. A mother, carrying and often dropping and damaging her infant, has to fend for herself. That means that a female chimp can only manage one infant at a time. Her birth rate is very low. And the result is that chimps are barely able to maintain their population---they're becoming extinct. They've never been able to leave the forest where they evolved."

Lovejoy chomps on a hamburger as the spirit of our intergalactic explorer hovers somewhere overhead. "Early man, you see, faced the same problem. And evolutionarily speaking, there's only one way round it. Put up the calorie intake of the female," he says, waving lunch, "and allow her to spend more time parenting---preferably in a protected spot---so that she can take care of more than one infant at a time. The male, in other words, has got to start providing food. How can he do that? He can't carry it in his mouth, as foxes and birds do. He has to walk upright and use his hands. Why should he do that? What does he get in return? Reliable sex and reliable care for his genetic investment."

There are two essential differences between human females and the females of all other species. Humans don't advertise or announce when they are fertile---their rear ends don't go red. And they are continuously sexually receptive. A woman can and will take on a man more often than once a month. Lovejoy believes that those, too, were very early adaptations and that they must have appeared as part of one evolutionary package about the same time as male provisioning and general upright posture. And that would make good sense.

For if the female could find a way of concealing when she was fertile, she could manage to do two things: She could force her male to stay with her throughout her cycle, if high on his agenda was successfully producing children. And, at the same time, she could discourage strange males from competing with him and undermining his confidence in his paternity. Being willing all the time can now be added to this strategy as a reinforcer. For if the committed male can get it regularly enough from one source, he will give up any catting around he might still be inclined to do and concentrate on bringing home the necessary bacon to where he can get it. That is the beginning of recreational sex; and it has nothing to do, evolutionarily speaking, with its later history of philandery and one-night stands. Quite the contrary. It is the gilding of the lily, the final setting of the seal, on the bed-centered nuclear family.

And from it, all that we think of as human flows. "This new arrangement," continues Lovejoy, "is extremely democratic; with one on one, most males can now find mates. It enlarges the social group---which is a huge advantage. It's highly socializing, rather than antisocial, because you now have double parents, families, kinship systems: Everyone knows who belongs to whom. It allows for an extended infancy, which allows for a gradually developing brain. And it frees the hands, encourages the adoption of devices for carrying both food and babies and prepares the ground for later weapons and tools. It's also more fun. Because all those things that make for the enjoyment of sex are now selected for anything that reinforces the longterm pair bond: the prominent penis; female breasts permanently on display; face-to-face copulation; hairlessness; the pleasure of orgasm. All of those would serve to keep the male and female together and help their children become smart enough to survive."

We're smart because we're sexy. We're sexy because we're smart. And we're both because, 3,500,000 years ago, we divided up our labors and started down the road of monogamy together.

Virgin birth to parasites to sex to males to competition to different reproductive strategies to polygamy to division of labor to monogamy: This will have to do for our intergalactic female's first report. But it isn't quite the end of the story, as we'll be seeing later in this series. For human males and females are today less constant, and human societies are less monogamous than this scenario might suggest. There is more competition for sexual and other resources than there seems to have been at the dawn of the Pleistocene era. On the ground, in practice, we seem as various as those other monogamists, the birds: We have rapists, bigamists, adulterers, sneaky fuckers of both sexes, polygamists and even, in a few cases, the keepers of several husbands. For all this, though, we are basically monogamous---as most birds are. And it is from this that most of the sexual attitudes in humans derive.

Women are concerned with the extent to which a man can provide (a recent study asked working-class women what they found sexually attractive in their husbands, and the dominant themes in their answers were money and food). And they almost always marry an older man. Men, by contrast, want youth---for reproduction's sake---and fidelity; the primary motive in the killing of women by men is---in both Africa and the United States---reported to be suspected or actual female infidelity. That may seem like an imbalance, but those qualities have been selected for by both males and females for hundreds of thousands of generations: size, strength and ambition in men, and constancy, mothering abilities and nurturance in women. It is, in fact, a very delicate balance. How delicate can be seen in two species of birds, Wilson's phalarope and the jacana. In both, the males have been bred by the females to do much more than their fair share of parental care and in the case of the jacana they are kept in male harems. The females are the winners, you might think. But they are also the losers. For they are forced into competition with one another---now there aren't enough males to go around. The females have become larger, they are now in the protection business and they've become more brightly decorated than the males---at the aesthetic whim of their mates.

Later in the series, we'll be looking at how all this may affect---and effect---current relationships between the sexes. "If you want to examine a really primitive society," says Lovejoy, "look at the West." But, for the moment, we want to leave you with this: If you think human, think old. If human life is a day, then the invention of the condom, let alone the pill, was less than a second ago. And if you think human, think rather of two sorts of human, bred over a succession of generations to express different skills and different abilities. Men and women are specialists. And in their differences lie the roots of their cooperation. In their cooperation lie the roots of our civilizations. We are as necessary and complementary to one another as the first egg and the first sperm.

But what are those differences? Some of them can be found in our bodies: We are specialists for different reproductive functions, specialists for one another's pleasure. But some of them can be found much deeper, at the heart of our behavior, in the organ that is fundamental to the biological inheritance that makes us who we are. In next month's issue we'll be looking at the most important sex organ of all: the brain. Are our brains as different as our bodies?

if females don't need males for reproduction, then why do males exist---and, for that matter, why is there sex at all?

"Billions of years ago, there must have been a switch to sex and it must have stuck. Why?"