The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature (28 page)

content ratings. There is a children's G-rated version of prehistory that eliminates all sex and most violence, where neither sexual selection nor natural selection have much force. Playmobil toy sets include multi-ethnic cave-men happily living alongside dinosaurs, hunting lions, and living in jungles. The
Flintstones
cartoons depicted a prehistory of capitalist affluence, suburban family values, and chaste monogamy. In these Gardens of Eden there is no hint of reproductive competition, the engine of evolution.

Then there is a "Parental Guidance" prehistory, with a bit more violence and a few coy allusions to romance. Our PG version of prehistory is usually compiled from
Planet of the Apes
films, television cartoons about time-traveling teenagers, school trips to

natural history museums, and summer camp experiences with the odd broken bone or stinging insect. Since this version emphasizes adventure, danger, and survival, it makes more plausible the idea that our minds evolved for toolmaking, hunting, and warfare. The resulting theory of human evolution resembles the opening sequence of Stanley Kubrick's
2001: A Space Odyssey
, in which proto-human apes conquer their rivals by inventing bone clubs, which put us straight on the technological path to moon-going spacecraft. The PG version never shows how the proto-humans produced any offspring, so sexual selection remains invisible.

Adult versions of prehistory include sexual content, but almost always in the form of a prurient male fantasy where female choice is irrelevant. Please, forget the sexual favors Raquel Welch bestowed on the dinosaur-slaying cave-man in the film
One Million Years B.C.
Do not take seriously the scene in
Quest for Fire
in which a rough stranger visiting a more sophisticated tribe is invited to copulate with all of the tribe's fertile women. Erase the memory of Daryl Hannah's rape by Neanderthals in
Clan of the Cave Bear.
The torrid paleolithic romances of Jean Auel are good entertainment, as are the erotic daydreams that may float through the minds of college students during springtime physical anthropology courses. However, they are not good touchstones for judging a theory of mental evolution through sexual choice.

Most media portrayals of prehistory follow one of three strategies: eliminate sexual content entirely, 'show cave-women falling for adventure heroes who rescue them from peril, or offer a narcissistic sexual fantasy in which only the protagonist (usually male) exercises sexual choice. There seems to be no market for portrayals of our early ancestors exerting mutual choice. If we are to see all the genuine tensions and difficulties between the sexes, media producers assume we must be rewarded with a proper costume drama set in- Imperial Rome or Regency England. After all, could Alan Rickman and Sigourney Weaver keep a straight face playing an intense romantic psychodrama set in Pleistocene Zaire, while wearing mangy furs, with ochre-smeared hair, and covered in ticks?

Maybe not, but a romantic psychodrama is just what we need to envision how sexual choice may have worked during human evolution. This is not a vain hope. In some ways we are better positioned to understand sexual selection than survival selection. The sexual challenges our ancestors faced were created by other members of their own species. Likewise today If our thoughts and feelings about sexual relationships are not too different from those of our ancestors, then our sexual challenges must not be too different. We get infatuated, we fall in love, we feel ecstatic, jealous, or heartbroken, we grow bored with some partners, and, if lucky, we develop a companionable attachment to the sexual partners with whom we raise children. We are attracted to beautiful faces and bodies, but also to a good sense of humor, a kind personality, a keen intelligence, and a high social status. If these sexual tastes are part of human nature that evolved gradually, our ancestors must have felt similarly to some degree. We should not automatically project modern social arrangements back into prehistory, but it is probably valid to project our individual emotions on to our ancestors.

By contrast, it can be difficult to appreciate the survival challenges that shaped our mental adaptations. In the developed world, we drive around in cars, live in the same house for years, use money to buy food, work hard at specialized jobs, and go to hospitals when ill. Our ancestors had to walk everywhere, lived in makeshift shelters in dozens of different places every year, did little work other than foraging for food, and when they fell ill, they either recovered spontaneously or died. The economics of surviving have changed dramatically, while the romantic challenges of mating have remained rather similar.

Pleistocene and Holocene

Why are evolutionary psychologists so preoccupied with the Pleistocene? The Pleistocene was a geological epoch uniquely important in human evolution, because it included the evolution of all, that is. distinctively human. At the beginning of the Pleistocene, 1.6 million years ago, our ancestors were still

relatively small-brained apes who walked upright and made just a few crude stone tools. They were almost certainly without language, music, art, or much creative intelligence. At the end of the Pleistocene, just 10,000 years ago, our ancestors were already modern humans, identical to us in bodily appearance, brain structure, and psychology. The evolution that shaped human nature all took place in the Pleistocene.

After the Pleistocene came the Holocene, occupying the last 10,000 years. The Holocene includes all of recorded history. During the Holocene, humans spread around the planet, invented agriculture, money, and civilization, and grew from populations of a few million to a few billion. The Holocene has been historically crucial but evolutionarily unimportant. Ten thousand years is only four hundred human generations, probably not enough time to evolve many new psychological adaptations. But it is plenty of time for runaway sexual selection to make populations diverge a bit in some aspects of body shape, facial appearance, and psychological traits. However, this book is not concerned with such relatively minor differences between populations. It is concerned with universal human mental abilities that our closest ape relatives do not share.

The Holocene changed patterns of human mating and reproduction dramatically It saw the emergence of inherited wealth, arranged marriages, hierarchical societies, patriarchy feminism, money, prostitution, monogamous marriage, harems, personal ads, telephones, contraception, and abortion. These make modern courtship rather different from Pleistocene courtship. But Pleistocene courtship is what drove sexual selection during the relevant period of human evolution, and human behavior in the Holocene still reflects our Pleistocene legacy.

Pleistocene Life

Knowing that the human mind's distinctive abilities evolved in the Pleistocene makes evolutionary psychology much easier. It means that all the ancestral environments that shaped the basic mental capacities of our species were physically contained within

the African continent, since all pre-human ancestors lived in Africa, and humans spread out of Africa only towards the end of the Pleistocene. Our ancestors lived in areas of sub-Saharan Africa that contained mixtures of open savanna, scrub, and forest. Instead of caves or jungles, picture Africa's broad, flat plains, with their baobabs and acacias, their wet and dry seasons, their hot days and cool nights, their plentiful hoofed herds and rare, emaciated predators, the incandescent sun, and millions of scrabbling insects.

A fairly coherent picture of Pleistocene life has emerged from anthropology, archeology, paleontology, primatology, and evolutionary psychology. Like other social primates, our hominid ancestors lived in small, mobile groups. Females and their children distributed themselves in relation to where the wild plant food grew, and clustered in groups for mutual protection against predators. Males distributed themselves in relation to where the females were. Many members of each group would have been blood relatives. Group membership may have varied daily and seasonally, according to opportunities for finding food and exploiting water sources.

Our ancestors would have known at least a hundred individuals very well by face and by personality. During their lifetimes they would have come into contact with several hundred or thousand members of the same local population. Almost all sexual partners would have been drawn from this larger tribal group, which, after language evolved, would probably have been identified by their shared dialect.

During the days, women would have gathered fruits, vegetables, tubers, berries, and nuts to feed themselves and their children. Men would have tried to show off by hunting game, usually unsuccessfully, returning home empty-handed to beg some yams from the more pragmatic womenfolk. Our ancestors probably did not have to work more than twenty or thirty hours a week to gather enough food to live. They did not have weekends or paid vacation time, but they probably had much more leisure time than we do.

There was intermittent danger from predators, parasites, and germs, but our ancestors would have become as accustomed to coping with those dangers as we are to crossing roads. Nature was not red in tooth and claw. Usually, it was really boring. Predators would have tended to kill the very young, the very ill, the very old, and the very foolish. Most illnesses would have been due to poor condition brought on by starvation or injury. Our ancestors did not spend all their time worrying about survival problems. They were among the longest-lived species on the planet, which implies that their daily risk of death was minuscule. Like most great apes, they probably spent their time worrying about social and sexual problems.

For most of evolution, our ancestors ranged across wide areas without being tied to a single home base or territory. They owned no more than they could carry, had no money, inherited no wealth, and could not store food today to insure against starvation next month. If individuals consistently appeared healthy, energetic, and well-fed, it was not because they were born rich. It must have been because they were good at foraging and good at making friends who took care of them during rough patches.

To understand how sexual selection may have operated in the Pleistocene, we have to ask how sexual relationships and sexual choice may have worked. We know that our hominid ancestors did not take each other out to restaurants and films, give each other engagement rings, or wear condoms. But what can we say about how they did select mates? We'll start with a look at sexual choice in other primates, and then consider what was distinctive about sexual choice among our hominid ancestors.

Sexual Selection in Primates

In most primate species, the distribution of food in the environment determines the distribution of females, and the distribution of females determines the distribution of males. When food is so dispersed that females do best by foraging on their own, males disperse to pair up with the lone females. This gives rise to monogamous couples. It is a fairly rare pattern among primates,

limited to gibbons, some lemurs, and some African and South American monkeys.

When food comes in patches large enough for several females to share, they tend to band together in small groups to find the food, and to protect each other against predators, unwanted males, and competing female groups. As long as the female band is not too large, a single male can exclude other males from sexual access to the band, which thus becomes "his." This "harem system" of single-male polygyny is fairly common in primates, being found in hamadryas baboons, colobus monkeys, some langurs, and gorillas. The competition between males to guard the female groups creates very strong sexual selection pressures for male size, strength, aggressiveness, and large canine teeth.

When food comes in still larger patches, female groups can grow too large for any single male to defend them. The males must then form coalitions, resulting in a complex multi-male, multi-female group, as in some baboons, macaques, ring-tailed lemurs, howler monkeys, and chimpanzees. Our hominid ancestors probably lived in such groups, in which sexual selection gets more complicated. Sometimes, females in multi-male groups appear to use sperm-production ability as the main fitness indicator. A chimpanzee female might mate with every male in the group every time she becomes fertile. She lets their sperm fight it out in her reproductive tract, and the strongest swimmers with the best endurance will probably fertilize her egg.

In response to this sexual selection for good sperm, male chimpanzees have evolved large testicles, copious ejaculates, and high sperm counts. Female primates face a trade-off. They can select for the best-swimming sperm by mating very promiscuously, or they can select for the best courtship behavior by mating very selectively. Or they can do a little of both, selecting a small group of male lovers for their charm and then letting their sperm fight it out.

In species that do not get completely caught up in runaway sperm competition, females can favor various male behavioral traits. Multi-male groups obviously allow greater scope for

females to choose between males. If they favor dominant males, males evolve through sexual selection to compete intensely for social status by individual force or by forming coalitions. If females favor kind males, males evolve through sexual selection to groom females, protect their offspring, and guard them from other males.

Given multi-male, multi-female primate groups, how does mate choice work? Female primates can exercise choice by joining groups that contain favored males, initiating sex with them during estrus, supporting them during conflicts, and developing long-term social relationships with them. Females can reject unfavored males by refusing to cooperate during copulation attempts, driving males away from the group, or leaving the group. But female mate choice criteria remain obscure for most primate species. In contrast to modern humans, female primates rarely favor males who can provide resources or paternal care of offspring. The sporadic male care that is observed, such as watching, carrying, and protecting infants, is better described as courtship effort than as paternal care. The male is unlikely to be the infant's father, but is simply trying to mate with the infant's mother by doing her a favor.