Why is Sex Fun?: the evolution of human sexuality

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.