The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature (47 page)

Aristophanes' play
Lysistrata
of 411 B.C. illustrated the moral power of female sexual choice. Lysistrata convinced the other women of Athens to stop having sex with their men until the men stopped waging the Peloponnesian war. The women barricaded themselves in the Acropolis, while (in the original staging of the play) the sex-starved men wandered around with ever-larger leather phalluses, gradually realizing that military victory becomes meaningless without the prospect of sex. Although some women were also tempted to break the sex strike—one even tried to sneak off to a brothel—they outlasted the men. Lysistrata's sex-strike succeeded in forcing the Athenian men to make peace with the Spartans. Her strategy would have worked equally well over evolutionary time: female sexual preferences for peace-keepers could have reduced male belligerence and aggressiveness.

This "better morality through mate choice" hypothesis prompts several questions. Why would mate choice mechanisms evolve to favor displays of generosity, fair play, good manners, or heroism? Why do we consider such displays especially "moral," as compared with other courtship displays? Why do our judgments of different courtship displays feel so different? Bodily ornaments seem to provoke lust, artistic displays induce aesthetic feelings, and moralistic displays attract admiration. This chapter does not answer all these questions, but may chart some new territory in the evolution of human morality. We'll start with a simple example of how mate choice can favor costly behaviors that provide for the common good.

The Evolution of Hunting:

An Altruistic Display of Athleticism?

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.

Blood Sports and Arabian Babblers

One perspective is that hunting should be regarded as just another competitive male sport, a contest in which winners can attract mates by demonstrating their athletic prowess. As we saw in Chapter 7, men spend huge amounts of time and energy doing useless sweaty things with one another: basketball, sumo, cricket, skiing, tae kwon do, mountaineering, boxing. To an evolutionist, male human sports are just another form of ritualized male contest in which males compete to display their fitness to females through physical dominance. From a female's point of view, sports are convenient because they make mate choice easier. She can tell which male is healthier, stronger, more coordinated, and more skillful by seeing who wins these ritualized contests. She doesn't need to weigh six hundred pounds to test a man's sumo ability herself; the other sumo wrestlers do it for her. Now that most of the cultural barriers against women participating in sports have fallen, men can equally assess a woman's physical fitness by observing her athletic abilities.

Now, consider two groups of hominids that evolve to prefer different sports. Suppose that one group prefers the club-fighting sport favored by the Yanomamo tribe of the Amazon: the males stand facing each other and take turns at bashing their opponent's head with a very long stick until one contestant gives up, faints, or drops dead. The females prefer mating with the winner, since he may have stronger arms, better aim, a thicker skull, or a pulse. Despite its wastefulness in terms of blood, death, and unsightly cranial scars, this is a perfectly good system of competitive courtship display, no worse than stags bashing their antlers together. The second group develops a different sport: they compete to

sneak up on big animals, throw spears at them, and chase the wounded animals until they drop dead. The females prefer mating with the successful animal-killers, since they are better at tracking, sneaking, spear-throwing, and running long distances. Here again, the competitive display system is wasteful: the males may spend all day, every day, chasing around after big animals, getting injured, getting tired, stumbling into thorn bushes, dropping spears, being gored by buffalo, and so forth. And yet, the hunting sport is not quite as wasteful as the club-fighting sport, because after a successful hunt there is this big carcass that a group can eat. Within each group, all individuals may be acting selfishly, competing to display their fitness, and choosing the highest-fitness mates they can. But the extra meat gives every gene and every individual in the hunting group a slight advantage over those in the club-fighting group. Over many generations, this advantage may lead to more groups hunting than club-fighting as the principal form of athletic display.

This process sounds like "group selection," which most biologists have rejected since the 1960s, but it is not quite the same. In traditional theories of group selection, competition between groups could supposedly lead individuals to sacrifice some of their own survival and reproduction prospects for the greater good of their group. In these theories, there was assumed to be a direct conflict between individual self-interest and group interest. But in this example of hunting versus club-fighting there is no such conflict. In both groups, all individuals are selfishly trying to attain the highest sexual status they can through ritualized sports; it just happens that one sport yields a higher group-level payoff than the other sport.

Another perspective on the provisioning of public goods comes from some songbirds that live in Israel. The birds are called Arabian babblers. They weigh three ounces, they live in big groups, and they are the stars of
The Handicap Principle
by Amotz and Avishag Zahavi. The Zahavis have studied babblers for three decades, and report that the birds behave in several ways that look altruistic. Some act as sentinels for the group, giving alarm calls

when predators approach. If a predator approaches, they mob the intruder, trying to drive it away. They share food with non-relatives. They practice communal nest care, taking care of babies that are not their offspring, kibbutz-style. They look like paragons of avian virtue, with altruism as conspicuous as a peacock's tail.

What is going on? Kin selection can't explain it, because the birds are kind to non-relatives. Reciprocity theory would predict that the birds would try to cheat, reaping the group benefits without paying the individual costs of being sentinels, mobbing predators, sharing food, or caring for nestlings. Instead, the birds do the opposite: they compete to perform the apparently altruistic behaviors. The Zahavis report that dominant animals, upon seeing a subordinate trying to act as a sentinel, will attack and drive off the subordinate, taking over the sentinel role. The birds try to stuff food down the throats of well-fed non-relatives. The Zahavis propose that the birds are using these altruistic acts as handicaps to display their fitness, thereby attaining higher social status in the group and improving their reproductive prospects. Only the birds in the best condition with the highest fitness can afford to act altruistically. Individuals seeking a mate can find good genes by finding a good altruist. That is how altruism apparently evolved in babblers. Most bird species do not appear to display their fitness by carrying out such pro-social good works. But those that do may have significant advantages, both as individuals and as groups.

John Nash Versus the Taxi Drivers of Bangalore

The altruistic human hunters and altruistic babbler birds are two outcomes of a very important evolutionary process called "equilibrium selection." It is an intimidating term, not widely understood even by biologists who have read some game theory. But I think the idea can clarify many mysteries, not only in evolution but in human culture.