The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature (4 page)

The first problem is that really large brains and complex minds arose very late in evolution and in very few species. Life evolved relatively quickly after the Earth cooled from a molten blob to a planet with a stable surface and some pools of water. Then it was another three billion years before any animal evolved a brain heavier than one pound. Even then, brains heavier than a pound evolved only in the great apes, in several varieties of elephants and mammoths, and in a few dozen species of dolphins and whales. Chimpanzee brains weigh one pound, our brains weigh three pounds, bottlenose dolphin brains weigh four pounds, elephant brains weigh eleven pounds, and sperm whale brains weigh eighteen pounds. But over 99 percent of animal species thrive with brains much smaller than a chimpanzee's. Far from showing any general trend towards big-brained hyper-intelligence, evolution seems to abhor our sort of intelligence, and avoids it whenever possible. So, why would evolution endow our species with such large brains that cost so much energy to run, given that the vast majority of successful animal species survive perfectly well with tiny brains?

Second, there was a very long lag between the brain's expansion and its apparent survival payoffs during human evolution. Brain size tripled in our ancestors between two and a half million years ago and a hundred thousand years ago. Yet for most of this period our ancestors continued to make the same kind of stone handaxes. Technological innovation was at a standstill during most of our brain evolution. Only long after our brains stopped expanding did any tradition of cumulative technological progress develop, or any global colonization beyond the middle latitudes, or any population growth beyond a few million individuals. Arguably, one could not ask for a worse correlation between growth in a biological organ and evidence of its supposed survival benefits. Our ancestors of a

hundred thousand years ago were already anatomically modern humans with bodies and brains just like ours. Yet they did not invent agriculture for another ninety thousand years, or urban civilization for another ninety-five thousand years. How could evolution favor the expansion of a costly organ like the brain, without any major survival benefits becoming apparent until long after the organ stopped expanding?

The third problem is that nobody has been able to suggest any plausible survival payoffs for most of the things that human minds are uniquely good at, such as humor, story-telling, gossip, art, music, self-consciousness, ornate language, imaginative ideologies, religion, and morality. How could evolution favor such apparently useless embellishments? The fact that there are no good theories of these adaptations is one of science's secrets. Linguistics textbooks do not include a good evolutionary theory of language origins, because there are none. Cultural anthropology textbooks present no good evolutionary theories of art, music, or religion, because there are none. Psychology textbooks do not offer any good evolutionary theories of human intelligence, creativity, or consciousness, because there are none. The things that we most want to explain in any evolutionary framework seem the most resistant to any such explanation. This has been one of the greatest obstacles to achieving any real coherence in human knowledge, to building any load-bearing bridges between the natural sciences, the social sciences, and the humanities.

These three problems compound one another. They roam around like a gang, knocking the sense out of any innocent young theories that happen to stroll along. If a new theory overcomes problem three by claiming a previously unrecognized survival benefit for art or language, then problem one raises the objection, "Why do we not see hundreds of species taking advantage of that survival benefit by growing larger brains with these abilities?'
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Or, suppose a new theory tackles problem two by emphasizing the success if our early
Homo erectus
ancestors in spreading from equatorial Africa across similar latitudes in Asia. Then problem three can point out that many smaller-brained mammals such as

cats and monkeys expanded in similar ways, without evolving such mental embellishments.

Most theories of human evolution attempt to solve only one of these three problems. A few might solve two. None has ever solved all three. This is because the three problems create a paradox that cannot be solved by thinking in terms of survival of the fittest. Many human mental abilities are unique to our species, but evolution is opportunistic and even-handed. It doesn't discriminate between species. If our unique abilities must be explained through some survival benefit, we can always ask why evolution did not confer that same benefit on many other species. Adaptations that have large survival benefits typically evolve many times in many different lineages, in a process called convergent evolution. Eyes, ears, claws, and wings have evolved over and over again in many different lineages at many different points in evolutionary history. If the human mind evolved mostly for survival benefits, we might expect convergent evolution to have driven many lineages toward human-type minds. Yet there is no sign of convergent evolution toward human-style language, moral idealism, humor, or representational art.

In
The Language Instinct,
Steven Pinker claimed that the elephant's trunk raises some of the same problems as human language: it is a large, complex adaptation that arose relatively recently in evolution, in only one group of mammals. Yet the elephant's trunk does not really raise any of our three problems. There was convergent evolution towards grasping tentacle-like structures among octopi and squid. The evolution of the trunk allowed the ancestors of the elephant to split apart very quickly into dozens of species of mammoths, mastodons, and elephants, in an evolutionary pattern called an "adaptive radiation." These species all had trunks, and they thrived all over the globe until our ancestors hunted them to extinction. An elephant uses its trunk every day to convey leaves from trees to mouth, showing clear survival benefits during foraging. The trouble with our unique human abilities is that they do not show the standard features of survival adaptations—convergent evolution, adaptive radiation, and obvious survival utility—and so are hard to explain through natural selection.

Sexual selection cuts through this Gordian knot. Biologists recognize that sexual selection through mate choice is a fickle, unpredictable, diversifying process. It takes species that make their livings in nearly identical ways and gives them radically different sexual ornaments. It never happens the same way twice. It drives divergent rather than convergent evolution. There are probably half a million species of beetle, but no two have the same kind of sexual ornamentation. There are more than three hundred species of primates, but no two have the same shape and color of facial hair. If the human mind's most unusual capacities evolved originally as courtship ornaments, their uniqueness comes as no surprise. Nor should we be surprised at the lack of survival benefits while brain size was tripling. The brain's benefits were mainly reproductive.

We get confused about the human mind's biological functions because of a historical accident called human history. The courtship ornaments that our species happened to evolve, such as language and creativity, happened to yield some completely unanticipated survival benefits in the last few thousand years: agriculture, architecture, writing, metalworking, firearms, medicine, and microchips. The usefulness of these recent inventions tempts us to credit the mind with some general survival advantage. From the specific benefits of specific inventions, we infer a generic biological benefit from the mind's "capacity for culture." We imagine evolution toiling away for millions of years, aiming at human culture, confident that the energetic costs of large brains will someday pay off with the development of civilization. This is a terrible mistake. Evolution does not have a Protestant work ethic. It does not get tax credits for research and development. It cannot understand how a costly investment in big brains today may be justified by cultural riches tomorrow.

To understand the mind's evolution, it is probably best to forget everything one knows about human history and human civilization. Pretend that the last ten thousand years did not happen. Imagine the way our species was a hundred thousand

years ago. From the outside, they would look like just another group of large primates foraging around Africa, living in small bands, using a few simple tools. Even their courtship looks uneventful: a male and a female just sit together, their eyes meet, and they breathe at each other in odd staccato rhythms for several hours, until they start kissing or one gives up and goes away. But if one could understand their quiet, intricately patterned exhalations, one could appreciate what is going on. Between their balloon-shaped skulls pass back and forth a new kind of courtship signal, a communication system unlike anything else on the planet. A language. Instead of dancing around in physical space like normal animals, these primates use language to dance around in mindscapes of their own invention, playing with ideas.

Talking about themselves gave our ancestors a unique window into one another's thoughts and feelings, their past experiences and future plans. Any particular courtship conversation may look trivial, but consider the cumulative effects of millions of such conversations over thousands of generations. Genes for better conversational ability, more interesting thoughts, and more attractive feelings would spread because they were favored by sexual choice. Evolution found a way to act directly on the mental sophistication of this primate species, not through some unique combination of survival challenges, but through the species setting itself a strange new game of reproduction. They started selecting one another for their brains. Those brains won't invent literature or television for another hundred thousand years. They don't need to. They have one another.

The intellectual and technical achievements of our species in the last few thousand years depend on mental capacities and motivations originally shaped by sexual selection. Trained by years of explicit instruction, motivated by sophisticated status games, and with cultural records that allow knowledge to accumulate across generations, our sexually selected minds can produce incredible things such as Greek mathematics, Buddhist wisdom, British evolutionary biology, and Californian computer games. These achievements are not side-effects of having big

brains that can learn everything, but of having minds full of courtship adaptations that can be retrained and redirected to invent new ideas even when we are not in love.

Fossils, Stories, and Theories

Anyone presenting a theory about human mental evolution is usually expected to present a speculative chronology of what evolved when, and to show how the current fossil and archeological data support that chronology I will attempt neither, because I think these expectations have too often led theorists to miss the forest for the trees. The human mind is a collection of biological adaptations, and an evolutionary theory of the mind must, above all, explain what selection pressures constructed those adaptations. Chronology is of limited use, because knowing when an adaptation arose is often not very informative about why it arose. Fossil and archeological evidence has been enormously important in showing how many pre-human species evolved, when they evolved, where they lived, and what tools they made. This sort of evidence is crucial in putting human evolution in its biological and geological context, but it has not proven terribly useful in explaining why we have the mental adaptations that we do—and in some cases it can be misleading.

For example, an overreliance on archeological data may lead scientists to underestimate the antiquity of some of our most distinctive abilities. Many have assumed that if there is no archeological evidence for music, art, or language in a certain period, then there cannot have been any. Historically, European archeologists tended to focus on European sites, but we now know that our human ancestors colonized Europe tens of thousands of years after they first evolved in Africa a hundred thousand years ago. This Eurocentric bias led to the view that music, art, and language must be only about 35,000 years old. Some archeologists such as John Pfeiffer claimed there was an "Upper Paleolithic symbolic revolution" at this date, when humans supposedly learned how to think abstractly and symbolically, leading to a rapid emergence of art, music, language, ritual,

religion and technological innovation. If these human abilities emerged so recently in Europe, we would not expect to find them among African or Australian peoples—yet there is plenty of anthropological evidence that all humans everywhere in the world share the same basic capacities for visual, musical, linguistic, religious, and intellectual display The same over-conservative reasoning would lead us to say that human language must be only 4,000 years old, because the archeological evidence for writing goes back only that far.

Also, the fossil and archeological evidence is still very patchy and is accumulating very quickly, with new discoveries often undermining our interpretations of old findings. Physical evidence about human origins seems the most secure place to begin in theorizing about human evolution, but this security is largely illusory. Since 1994 at least four new species of hominid have been discovered. Every year brings new bones or stones that necessitate a major rethinking about the times, places, and products associated with human origins. The result is often theories as transient as the evidence they cite. Most human evolution theories of twenty or fifty years ago are barely worth reading now because, by tying themselves too closely to the physical evidence then available, they aimed too much for empirical respectability at the expense of theoretical coherence. The theories that remain relevant are those derived from fundamental principles of evolutionary biology and commonsense observations about the human mind. Darwin's thoughts on the human mind's evolution in
The Descent of Man
are still useful because he did not overreact to the new discoveries of Neanderthal skulls and living gorillas that fascinated Victorian London. Classic selection pressures are more important than classic fossils.