Why did humans evolve to hunt relatively big game like eland and mammoth? The answer seems pretty obvious: you can eat their meat and survive better. The 1968 anthropological classic Man the Hunter took the view that hunting evolved through simple survival selection. Hungry hominid? No problem—go hunt.
It turns out not to be that simple. In the early 1980s, female anthropologists contributed to a corrective volume entitled Woman the Gatherer. They showed that in most hunter-gatherer societies women provide most of the sustenance, efficiently collecting plant foods and small game. The men often fail to bring any meat back from the hunt and often rely on their female partners for day-to-day sustenance. Trying to chase down large mammals that have evolved to run away from predators much faster than you is just not an efficient, reliable way to support yourself, much less your family. Anthropologist Kristen Hawkes found that in the tribe she was studying, men have only a 3 percent chance per day of successfully killing a large animal. That's 97 percent failure: not the stereotypical image of the cave-man bringing home the bacon. Data from other tribes shows slightly higher success rates, but they rarely exceed 10 percent each day.
To a female gatherer seeking a bit of meat on the side, the behavior of the males must be doubly annoying. If they must hunt to boost their egos, fine, but why must they try to catch really big animals? Men know very well that their hunting success is much higher when they go after smaller, slower, weaker animals. Usually, the smaller the prey they target, the more pounds of meat per day they bring home, and the less variable is the amount of meat from one week to the next. Also, the smaller the game, the more of its meat can be eaten before it goes rotten. When hunters really need to eat, they'll give up on the large game and catch the small. If hunting's function is to feed the hunter and his family, male human hunters look ridiculously overambitious. They aim for giraffes when they should be catching gophers.
Chimpanzee males hunt monkeys, but monkeys are little, so the chimps have more control over the distribution of their meat. The best predictor of male chimpanzee hunting effort is the number of females in the group that are currently in estrus, showing large red genital swellings. Males try to induce fertile females to mate with them by catching meat to give to them. Hunting in our closest living ape relatives apparently evolved through sexual selection. But male humans go after much bigger game than male chimps do, with a lower success rate and much less control over meat distribution.
Does meat from large game contain some special nutrient unavailable from small game or plants? If so, perhaps it makes sense for couples to split the work of feeding their families, for men to specialize in big-game hunting to get that precious nutrient, and for women to specialize in gathering the more dependable plant resources. In this vision of hunting's evolution, women demand meat in exchange for sex. Anthropologist Helen Fisher has even proposed that this was the first human contractual relationship, in her 1982 book The Sex Contract. Owen Lovejoy had a similar theory, that male hunting provided meat for sexual partners burdened by babies, whose gathering efficiency would suffer while they were breastfeeding. For a long time this sex-for-meat theory seemed reasonable. Many theorists even proposed that male hunting allowed humans to bear the nutritional burdens of evolving a larger brain: as long as men transferred enough protein to dependent offspring, those offspring could grow smarter. Note that even in this traditional theory, female choice drives the evolution of hunting. Women refuse sex to men who fail to bring home meat. They force men to invest paternal effort in their offspring, helping to bear the nutritional costs of raising their offspring.
There is another problem, though: even if men manage to kill a large animal, they cannot control how its meat is distributed. The bigger the kill, the harder it is for a hunter to make sure that the meat goes to his girlfriends and their babies. Anthropologists observe that in almost all tribal cultures, meat is shared very widely among tribe members. People come running when they hear of a successful kill or see the vultures circling. They demand their share, aggressively and insistently. Often the amount of meat the hunter gets is statistically indistinguishable from anyone else's share. After perhaps a month's hunting effort, the hunter gets around 10 percent of the carcass, around 20 to 30 pounds of meat that must be consumed within a few days before it rots. Within a week, he'll be hungry again. Good hunters are not just reciprocal altruists, because bad hunters will never manage to repay them for the meat they take, and reciprocity would favor hunting small game that was easier to defend from cheats.
Anthropologist Kristen Hawkes has argued that meat from large game is a "public good" in the technical economic sense: a resource that one cannot exclude others from consuming. When anthropologists considered meat a private good, with the hunter able to control its distribution and consumption, hunting seemed to make evolutionary sense as a way of supporting one's family. But meat as a public good seems to create a paradox. Hunting's costs are borne by the hunter: the time and energy spent learning how to hunt, making the weapons, tracking the animals, using the weapons, and running down wounded prey. The hunter also risks injury or death from an animal that is fighting for its life, when he is merely hunting for his dinner. Yet hunting's benefits are spread throughout the tribe, enjoyed by sexual competitors and unrelated offspring. Evolution cannot generally favor genetic tendencies to provide public goods at the expense of one's own genetic interests. Such a tendency would fit the definition of evolutionary altruism, which cannot evolve by any known natural process.
So we have a quandary. At first, hunting looked to be a simple matter of survival. Then it looked to be a simple case of sexual selection, a meat-for-sex exchange, a way for women to transform male courtship effort into paternal effort. Now it looks more like a risky, wasteful act of altruism, a way for males to feed their sexual competitors (and other members of their band) at high risk to themselves. All three of these views have some merit and some supporting evidence. Here I have focused on the apparently altruistic aspects of hunting, not because I am interested in hunting per se, but because it raises a more general issue: how could selfish genes possibly give rise to costly, seemingly altruistic forms of charity? We'll triangulate toward the answer from three directions: the analogy between hunting and sports, the behavior of birds called Arabian babblers, and the concept of equilibrium selection from game theory These ideas will prove useful not only for explaining human morality but also, later on, for explaining the evolution of language.
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