Why is Sex Fun?: the evolution of human sexuality (5 page)

All three factors-sex differences in obligate parental investment, alternative opportunities foreclosed by child care, and confidence in parenthood-contribute to making men much more prone than women to desert a spouse and child. However, a man is not like a male hummingbird, male tiger, or the male of many other animal species, who can safely fly or walk away immediately after copulation, secure in the knowledge that his deserted female sex partner will be able to handle all the ensuing work of promoting the survival of his genes. Human infants virtually need biparental care, especially in traditional societies. While we shall see in chapter 5 that activities represented as male parental care may actually have more complex functions than meet the eye, many or most men in traditional societies do undoubtedly provide services to their children and spouse. Those services include: acquiring and delivering food; offering protection, not only against predators but also against other men who are sexually interested in a mother and regard her offspring (their potential stepchildren) as a competing genetic nuisance; owning land and making its produce available; building a house, clearing a garden, and performing other useful labor; and educating children, especially sons, so as to increase the children's chances of survival.

Sex differences in the genetic value of parental care to the parent provide a biological basis for the all-too-familiar differing attitudes of men and women toward extramarital sex. Because a human child virtually required paternal care in traditional human societies, extramarital sex is most profitable for a man if it is with a married woman whose husband will unknowingly rear the resulting child. Casual sex between a man and a married woman tends to increase the man's output of children, but not the woman's. That decisive difference is reflected in men's and women's differing motivations. Attitude surveys in a wide variety of human societies around the world have shown that men tend to be more interested than women in sexual variety, including casual sex and brief relationships. That attitude is readily understandable because it tends to maximize transmission of the genes of a man but not of a woman. In contrast, the motivation of a woman participating in extramarital sex is more often self-reported as marital dissatisfaction. Such a woman tends to be searching for a new lasting relationship: either a new marriage or a lengthy extramarital relationship with a man better able than her husband to provide resources or good genes.

Last year I received a remarkable letter from a professor at a university in a distant city, inviting me to an academic conference. I did not know the writer, and I couldn't even figure out from the name whether the writer was a man or a woman. The conference would involve long plane flights and a week away from home. However, the letter of invitation was beautifully written. If the conference was going to be as beautifully organized, it might be exceptionally interesting. With some ambivalence because of the time commitment, I accepted.

My ambivalence vanished when I arrived at the conference, which turned out to be every bit as interesting as I had anticipated. In addition, much effort had been made to arrange outside activities for me, including shopping, bird-watching, banquets, and tours of archaeological sites. The professor behind this masterpiece of organization and the original virtuoso letter proved to be a woman. In addition to giving a brilliant lecture at the conference and being a very pleasant person, she was among the most stunningly beautiful women I had ever met.

On one of the shopping trips that my hostess arranged, I bought several presents for my wife. The student who had been sent along as my guide evidently reported purchases to my hostess, because she commented on them when I sat next to her at the conference banquet. To my astonishment, she told me, “My husband never buys me any presents!” She had formerly bought presents for him but eventually stopped when he never reciprocated.

Someone across the table then asked me about my field-work on birds of paradise in New Guinea. I explained that male birds of paradise provide no help in rearing the nestlings but instead devote their time to trying to seduce as many females as possible. Surprising me again, my hostess burst out, “Just like men!” She explained that her own husband was much better than most men, because he encouraged her career aspirations. However, he spent most evenings with other men from his office, watched television while at home on the weekend, and avoided helping with the household and with their two children. She had repeatedly asked him to help; she finally gave up and hired a housekeeper. There is, of course, nothing unusual about this story. It stands out in my mind only because this woman was so beautiful, nice, and talented that one might naively have expected the man who chose to marry her to have remained interested in spending time with her.

My hostess nevertheless enjoys much better domestic conditions than do many other wives. When I first began to work in the New Guinea highlands, I often felt enraged at the sight of gross abuse of women. Married couples whom I encountered along jungle trails typically consisted of a woman bent under an enormous load of firewood, vegetables, and an infant, while her husband sauntered along upright, bearing nothing more than his bow and arrow. Men's hunting trips seemed to yield little more than male bonding opportunities, plus some prey animals immediately consumed in the jungle by the men. Wives were bought, sold, and discarded without their consent.

Later, though, when I had children of my own and sensed my feelings as I shepherded my family on walks, I thought that I could better understand the New Guinea men striding beside their families. I found myself striding next to my own children, devoting all my attention to mak-ing sure that they did not get run over, fall, wander off, or suffer some other mishap. Traditional New Guinea men had to be even more attentive because of the greator risks facing their children and wives. Those seemingly carefree men strolling along beside a heavily burdened wife were actually functioning as lookouts and protectors, keeping their hands free so that they could quickly deploy their bow and arrow in the event of ambush by men of another tribe. But the men's hunting trips, and the sale of women as wives, continue to trouble me.

To ask what men are good for may sound like a flip one-liner. In fact, the question touches a raw nerve in our society. Women are becoming intolerant of men's self-ascribed status and are criticizing those men who provide better for themselves than for their wives and children. The question also poses a big theoretical problem for anthropologists. By the criterion of services offered to mates and children, males of most mammal species are good for nothing except injecting sperm. They part from the female after copulation, leaving her to bear the entire burden of feeding, protecting, and training the offspring. But human males differ by (usually or often) remaining with their mate and offspring after copulation. Anthropologists widely assume that men's resulting added roles contributed crucially to the evolution of our species' most distinctive features. The reasoning goes as follows.

The economic roles of men and women are differentiated in all surviving hunter-gatherer societies, a category that encompassed all human societies until the rise of agriculture ten thousand years ago. Men invariably spend more time hunting large animals, while women spend more time gathering plant foods and small animals and caring for children. Anthropologists traditionally view this ubiquitous differentiation as a division of labor that promotes the nuclear family's joint interests and thereby represents a sound strategy of cooperation. Men are much better able than women to track and kill big animals, for the obvious reasons that men don't have to carry infants around to nurse them and that men are on the average more muscular than women. In the view of anthropologists, men hunt in order to provide meat to their wives and children.

A similar division of labor persists in modern industrial societies: many women still devote more time to child care than men do. While men no longer hunt as their main occupation, they still bring food to their spouse and children by holding money-paying jobs (as do a majority of American women as well). Thus, the expression “bringing home the bacon” has a profound and ancient meaning.

Meat provisioning by traditional hunters is considered a distinctive function of human males, shared with only a few of our fellow mammal species such as wolves and African hunting dogs. It is commonly assumed to be linked to other universal features of human societies that distinguish us from our fellow mammals. In particular, it is linked to the fact that men and women remain associated in nuclear families after copulation, and that human children (unlike young apes) remain unable to obtain their own food for many years after weaning.

This theory, which seems so obvious that its correctness is generally taken for granted, makes two straightforward predictions about men's hunting. First, if the main purpose of hunting is to bring meat to the hunter's family, men should pursue the hunting strategy that reliably yields the most meat. Hence we should observe that men are on the average bagging more pounds of meat per day by going after big animals than they would bring home by targeting small animals. Second, we should observe that a hunter brings his kill to his wife and kids, or at least shares it preferentially with them rather than with nonrelatives. Are these two predictions true?

Surprisingly for such basic assumptions of anthropology, these predictions have been little tested. Perhaps unsurprisingly, the lead in testing them has been taken by a woman anthropologist, Kristen Hawkes of the University of Utah. Hawkes's tests have been based especially on quantitative measurements of foraging yields for Paraguay's Northern Ache Indians, carried out jointly with Kim Hill, A. Magdalena Hurtado, and H. Kaplan. Hawkes performed other tests on Tanzania's Hadza people in collaboration with Nicholas Blurton Jones and James O'Connell. Let's consider first the evidence for the Ache.

The Northern Ache used to be full-time hunter-gatherers and continued to spend much time foraging in the forest even after they began to settle at mission agricultural settlements in the 1970s. In accord with the usual human pattern, Ache men specialize in hunting large mammals, such as peccaries and deer, and they also collect masses of honey from bees' nests. Women pound starch from palm trees, gather fruits and insect larvae, and care for children. An Ache man's hunting bag varies greatly from day to day: he brings home food enough for many people if he kills a peccary or finds a beehive, but he gets nothing at all on one-quarter of the days he spends hunting. In contrast, women's returns are predictable and vary little from day to day because palms are abundant; how much starch a woman gets is mainly a function of just how much time she spends pounding it. A woman can always count on getting enough for herself and her children, but she can never reap a bonanza big enough to feed many others.

The first surprising result from the studies by Hawkes and her colleagues concerned the difference between the returns achieved by men's and women's strategies. Peak yields were, of course, much higher for men than for women, since a man's daily bag topped 40,000 calories when he was lucky enough to kill a peccary. However, a man's average daily return of 9,634 calories proved to be lower than that of a woman (10,356), and a man's median return (4,663 calories per day) was much lower. The reason for this paradoxical result is that the glorious days when a man bagged a peccary were greatly outnumbered by the humiliating days when he returned empty-handed.

Thus, Ache men would do better in the long run by sticking to the unheroic “woman's job” of pounding palms than by their devotion to the excitement of the chase. Since men are stronger than women, they could pound even more daily calories of palm starch than can women, if they chose to do so. In going for high but very unpredictable stakes, Ache men can be compared to gamblers who aim for the jackpot: in the long run, gamblers would do much better by putting their money in the bank and collecting the boringly predictable interest.

The other surprise was that successful Ache hunters do not bring meat home mainly for their wives and kids but share it widely with anyone around. The same is true for men's finds of honey. As a result of this widespread sharing, three-quarters of all the food that an Ache consumes is acquired by someone outside his or her nuclear family.

It's easy to understand why Ache women aren't big-game hunters: they can't spend the time away from their children, and they can't afford the risk of going even a day with an empty bag, which would jeopardize lactation and pregnancy. But why does a man eschew palm starch, settle for the lower average return from hunting, and not bring home his catch to his wife and kids, as the traditional view of anthropologists predicts?

This paradox suggests that something other than the best interests of his wife and children lie behind an Ache man's preference for big-game hunting. As Kristen Hawkes described these paradoxes to me, I developed an awful foreboding that the true explanation might prove less noble than the male's mystique of bringing home the bacon. I be-gan to feel defensive on behalf of my fellow men and to search for explanations that might restore my faith in the nobility of the male strategy.

My first objection was that Kristen Hawkes's calculations of hunting returns were measured in calories. In reality, any nutritionally aware modern reader knows that not all calories are equal. Perhaps the purpose of big-game hunting lies in fulfilling our need for protein, which is more valuable to us nutritionally than the humble carbohydrates of palm starch. However, Ache men target not only protein-rich meat but also honey, whose carbohydrates are every bit as humble as those of palm starch. While Kalahari San men (“Bushmen”) are hunting big game, San women are gathering and preparing mongongo nuts, an excellent protein source. While lowland New Guinea hunter-gatherer men are wasting their days in the usually futile search for kangaroos, their wives and children are predictably acquiring protein in the form of fish, rats, grubs, and spiders. Why don't San and New Guinea men emulate their wives?

I next began to wonder whether Ache men might be unusually ineffective hunters, an aberration among modern hunter-gatherers. Undoubtedly, the hunting skills of Inuit (Eskimo) and Arctic Indian men are indispensable, especially in winter, when little food other than big game is available. Tanzania's Hadza men, unlike the Ache, achieve higher average returns by hunting big game rather than small game. But New Guinea men, like the Ache, persist in hunting even though yields are very low. And Hadza hunters persist in the face of enormous risks, since on the average they bag nothing at all on twenty-eight out of twenty-nine days spent hunting. A Hadza family could starve while waiting for the husband-father to win his gamble of bringing down a giraffe. In any case, all that meat occasionally bagged by a Hadza or Ache hunter isn't reserved for his family, so the question of whether big-game hunting yields higher or lower returns than alternative strategies is academic from his family's point of view. Big-game hunting just isn't the best way to feed a family.

Still seeking to defend my fellow men, I then wondered: could the purpose of widely sharing meat and honey be to smooth out hunting yields by means of reciprocal altruism? That is, I expect to kill a giraffe only every twenty-ninth day, and so does each of my hunter friends, but we all go off in different directions, and each of us is likely to kill his giraffe on a different day. If successful hunters agree to share meat with each other and their families, all of them will often have full bellies. By that interpretation, hunters should prefer to share their catch with the best other hunters, from whom they are most likely to receive meat some other day in return.

In reality, though, successful Ache and Hadza hunters share their catch with anyone around, whether he's a good or hopeless hunter. That raises the question of why an Ache or Hadza man bothers to hunt at all, since he can claim a share of meat even if he never bags anything himself. Conversely, why should he hunt when any animal that he kills will be shared widely? Why doesn't he just gather nuts and rats, which he can bring to his family and would not have to share with anyone else? There must be some ignoble motive for male hunting that I was overlooking in my efforts to find a noble motive.

As another possible noble motive, I thought that widespread sharing of meat helps the hunter's whole tribe, which is likely to flourish or perish together. It's not enough to concentrate on nourishing your own family if the rest of your tribe is starving and can't fend off an attack by tribal enemies. This possible motive, though, returns us to the original paradox: the best way for the whole Ache tribe to become well nourished is for everybody to humble themselves by pounding good old reliable palm starch and collecting fruit or insect larvae. The men shouldn't waste their time gambling on the occasional peccary.