The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature (6 page)

Many recent books about the human mind's evolution have offered radical new ideas about how evolution works, but have described the mind's capacities very conservatively. That approach suggests that modern evolutionary theory is a castle built on sand, whereas modern psychology is the Rock of Gibraltar. I take the opposite view. Mostly, my sexual choice theory relies on conservative, well-established evolutionary principles, but it takes a rather playful, irreverent view of human behavior.

This book also draws on a wide range of facts and ideas from

many areas of science, including psychology anthropology evolutionary theory primatology archeology cognitive science, game theory and behavior genetics. I also borrow a number of ideas from contemporary feminism and cultural theory and from some of my intellectual heroes such as Friedrich Nietzsche and Thorstein Veblen. I won't pretend to be expert in all these topics. Outside our own areas of expertise, scientists keep up to date by reading the same popular science books and magazine articles as other people do. This makes us vulnerable to the same intellectual fads that sweep through academic and popular culture; it also makes us dependent on the popularizers of other sciences, who sometimes have idiosyncratic views. I have tried to minimize such distortions by being fairly conservative about which ideas and data I rely on. I try to identify which of my arguments are well supported by the current evidence as I understand it, and which still need to be evaluated with further research.

There are also limits to my practical understanding of our

mental adaptations. I know less about art than most artists, less

about language than political speech writers, and less about comedy than Matt Groening, originator of
The Simpsons.
If you find that you know more about some aspect of the human mind than I do, my errors and omissions could be considered your opportunities. There is plenty of room in evolutionary psychology

for contributions by people with all sorts of expertise.

This book presents one possible way to apply sexual selection theory in evolutionary psychology, but there are countless other ways. There is no pretense here of having a complete theory of the human mind, human evolution, or human sexual relationships. This is a snapshot of a provisional theory under construction. My aim is to stimulate discussion, debate, and further research, not to win people over to some doctrine set in stone.

An Ancestral Romance

This book's most unusual challenge is that readers will sometimes be asked to imagine what it was like for our ancestors to fall in love with beings considerably hairier, shorter, poorer, less creative, less

articulate, and less self-conscious than ourselves. This is best done without visualizing such beings too concretely. I have never managed to feel genuine desire for any museum model of an Australopithecine female, however realistically their sloping foreheads, thick waists, and furry buttocks have been rendered. Nor have I found it easy to imagine feeling genuine love when gazing into the eyes of one of these ancestors from three million years ago. Our sexual preferences seem too hard-wired to permit these imaginative leaps. The limits of our contemporary sexual imaginations have always been an obstacle to appreciating the role of sexual choice in human evolution.

On the other hand, ancestral romance is not so hard to understand at a slightly more abstract level. Indeed, it may be intuitively easier to understand human evolution through sexual selection than through natural selection. While our ancestors faced very different survival problems than we do today, the problems of sexual rejection, heartbreak, jealousy, and sexual competition remain almost unchanged. Few of us have any experience digging tubers, butchering animals, escaping from lions, or raiding other tribes. But our past sexual relationships may prove a useful guide to understanding the sexual choices that shaped our species.

Each of our romantic histories goes back only a few years, but the romantic history of our genes goes back millions. We are here only because our genes enjoyed an unbroken series of successful sexual relationships in every single generation since animals with eyes and brains first evolved half a billion years ago. In each generation, our genes had to pass through a gateway called sexual choice. Human evolution is the story of how that gateway evolved new security systems, and how our minds evolved to charm our way past the ever more vigilant gatekeepers.

2

Darwin's Prodigy

The idea of sexual selection has a peculiar history that embodies the best and the worst of science. The best, because it follows the classic heroic model. A lone genius (Charles Darwin), working from his country home without any official academic position, proposes a bold theory that explains diverse, previously baffling facts. Despite presenting the theory in a lucid, engaging best-seller (
The Descent of Man, and Selection in Relation to Sex
)
,
the theory is immediately attacked, mocked, reviled, and dismissed by his narrow-minded colleagues. The theory falls into obscurity, but, as decades pass, more and more supporting evidence accumulates in ways that could never have been anticipated by the original thinker. Finally, over a century after it is first proposed, the theory gradually becomes accepted as a major, original contribution. Sexual selection theory has returned like the prodigal son. Science shows once again how truth wins out against historical contingency and ideological hostility.

Yet this history also shows the worst of science. Over a century passed before biologists took seriously Darwin's most provocative ideas about mate choice. The delay resulted not just from rational skepticism, but from a set of reactionary prejudices deriving from sexism, anthropocentrism, and a misguided type of reductionism. These prejudices were so strong that, for more than fifty years after Darwin, virtually no biologists or psychologists bothered to put his mate choice ideas to a good experimental test (though such tests have subsequently proven fairly easy to do, usually with positive results).

This chapter introduces some basic sexual selection ideas

through a narrative history. The history is important because the century when sexual selection was in exile was the century when the origins of the human mind seemed the most inexplicable. Before Darwin, religious myths accounted for human origins; after Darwin, evolution satisfactorily accounted for the human body, but not the human mind. In the 20th century, a unique scientific fascination with human psychology coexisted with an unprecedented bafflement about its origins. By considering the 19th-century origins of sexual selection theory, we may better understand aspects of human nature that were overlooked for most of the 20th century.

Ornaments of Gold

As a child, Charles Darwin was fascinated by nature. He collected beetles avidly, and was once so determined to capture a specimen, despite having his hands full, that he placed it in his mouth to carry home. His reward was a mouthful of defensive beetle-acid, but his enthusiasm remained intact. His family estate, The Mount, near Shrewsbury, had an excellent library full of his father's natural history books, a greenhouse stocked with exotic plants, an aviary for the fancy pigeons his mother kept, and access to a bank of the River Severn. Young Charles preferred nature's sights and sounds to the rote learning of Latin at the local Shrewsbury School.

By age 23, Darwin had left Shrewsbury for South America. His round-the-world voyage on the
Beagle
introduced him to the astounding volume and diversity of nature's ornaments. England had passerine birds with intricate songs, and pheasants with stately colors, but nothing prepared the young naturalist for the richly ornamented flora and fauna of the tropics: iridescent humming birds visiting outlandish flowers; beetles with carapaces of gold, sapphire, and ruby; enigmatic orchids; screaming parrots; butterflies like two blue hands clapping; monkeys with red, white, black, and tan faces; exotic Brazilian fruits on market stalls. On a single day during a foray from Rio, Darwin caught no less than 68 species of beetle. His diaries record his "transports of pleasure

and the "chaos of delights" inspired by the jungle's baroque extravagance—"like a view in the Arabian Nights."

Darwin wanted an explanation for this rich array of diversity. Two decades before Darwin's trip, theologians such as William Paley had argued that God ornaments the world to inspire man's wonder and devotion. Darwin may have wondered why God would put tiny golden bugs in the heart of a sparsely populated jungle, a thousand miles from the nearest church. Were nature's ornaments really for our eyes only? Between the
Beagle's
voyage and his notebooks of 1838, Darwin had worked out the principle of evolution by natural selection. He realized that bugs must be golden for their own purposes, not to delight our eyes or to symbolize divine providence.

Animal ornaments must have evolved for some reason, but Darwin could not see how his new theory of natural selection could account for these seemingly useless luxuries. He had seen that many animals, especially males, have colorful plumage and melodious songs. These are often complex and costly traits. They usually have no apparent use in the animals' daily routine of feeding, fleeing, and fighting. The animals do not strive to display these ornaments to humans when we appear to need some spiritual inspiration. Instead, they display their beauty to the opposite sex. Usually, males display more. Peacocks spread their tails in front of peahens. In every European city, male pigeons harass female pigeons with relentless cooing and strutting. If the females go away, the male displays stop. If the female comes back, the males start again. Why?

Once his travels had confronted Darwin with the enigma of animal ornamentation, he could never take it for granted again. After his return, it seemed to him that English gardens were awash with peacocks. Their tails kept the problem in the forefront of

Darwin's mind, sometimes with nauseating effect. Darwin once confided to his son Francis that "The sight of a feather in a

peacock's tail, whenever I gaze at it, makes me sick!" The peacocks seemed to mock Darwin's theory that natural selection shapes every trait to some purpose.

Science by Stealth

Darwin cured his peacock-nausea by developing the theory of sexual selection. We do not know exactly when or how he developed it, because historians of science have not tried very hard to find out. They have written at least a thousand times as much about the discovery of natural selection as they have about the discovery of sexual selection. Even today, there is only one good history of sexual selection theory—Helena Cronin's
The Ant and the Peacock.
But we do know this: at some point between the
Beagle's
voyage in the 1830s and the publication of
The Origin of Species
in 1859, Darwin started to understand animal ornamentation. In that epoch-making book he felt comfortable enough about sexual selection to devote three pages to it, but not confident enough to give it a whole chapter.

From that acorn grew the oak: his 900-page, two-volume
The Descent of Man, and Selection in Relation to Sex
of 1871. The title is misleading. Less than a third of the book—only 250 pages—concerns our descent from ape-like ancestors. The rest concentrates on sexual selection, including 500 pages on sexual selection in other animals, and 70 pages on sexual selection in human evolution. Darwin was no longer troubled by tiny gold bugs or peacock feathers. He considered his sexual selection idea to be so important that he featured it in the one book he was sure humans would read: his summary of the evidence for human evolution.

However, Darwin was a subtle and strategic writer, often hiding his intentions. His introduction to
The Descent
claimed that "The sole object of this work is to consider, firstly, whether man, like every other species, is descended from some pre-existing form; secondly, the manner of his development; and thirdly, the value of the differences between the so-called races of man." Later in the introduction he pretended that his only reason for considering sexual selection was its utility in explaining human racial differences. He apologizes that "the second part of the present work, treating of sexual selection, has extended to an inordinate length, compared with the first part, but this could not be avoided." Immediately after claiming that he lacked the editorial

self-control to leave sexual selection for another book, he complained that lack of space required him to leave for another book his essay
The Expression of the Emotions in Man and Animals.
What was Darwin thinking?
The Expression of the Emotions
provided direct evidence of psychological similarities between humans and other animals. One would think it belonged in
The Descent,
if the book's sole object was to consider man's biological similarities to other animals. Yet Darwin left his best evidence of similarity for another book, and inserted almost 600 pages on sexual selection. I suspect that this was science by stealth. Perhaps Darwin intended to smuggle into popular consciousness his outrageous claim that mate choice guides evolution, while his relatively predictable views on human evolution would draw the fire of his critics. As we shall see, this clever plan was not entirely successful.

The Grand Gateway of Sex

So how does sexual selection explain ornamentation? Darwin's problem was the ubiquity of large, costly, complex traits like peacock's tails that seem to contribute nothing to an animal's survival ability. Natural selection, as Darwin defined it, arises from individual differences in survival ability. It cannot favor traits opposed to survival. Since most ornaments decrease an individual's survival ability, they presumably could not have evolved by natural selection for survival.