The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature by Geoffrey Miller Page A
Authors: Geoffrey Miller
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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.
This means that evolution must include some form of creative, trait-shaping selection other than natural selection. Darwin reasoned that in a sexually reproducing species, any traits that help in competing for sexual mates will tend to spread through the species. These traits may evolve even if they reduce survival ability. While natural selection adapts species to their environments, sexual selection shapes each sex in relation to the other sex. In The Origin, Darwin argued that sexual selection depends "not on a struggle for existence in relation to other organic beings or to external conditions, but on a struggle between the individuals of one sex, generally the males, for the possession of the other sex. The result is not death to the unsuccessful competitor, but few or no offspring."
Darwin didn't know about genes or DNA. But he understood that in a sexually reproducing species, the only way to pass a trait from one generation to the next was, by definition, through sexual reproduction. If an animal doesn't have sex, its heritable traits will die with it, and it will leave no hereditary trace in the next generation. As far as evolution is concerned, the animal may as well have died in infancy. Survival without reproduction means evolutionary oblivion. On the other hand, reproduction followed by death can still translate into evolutionary success. Sexual inheritance puts sexual reproduction at the heart of evolution. The concept of sexual selection is simply a way of describing how differences in reproductive success lead to evolutionary change.
Sexual, Natural, Artificial
To explain sexual selection, Darwin used the familiar metaphor of artificial selection. Victorian England was still mostly agricultural and pastoral. People knew about artificial selection, in which farmers domesticate plants and animals by allowing some individuals to breed and others not. Darwin had already used this barnyard type of artificial selection as a metaphor to explain how natural selection worked. Sexual
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.
This means that evolution must include some form of creative, trait-shaping selection other than natural selection. Darwin reasoned that in a sexually reproducing species, any traits that help in competing for sexual mates will tend to spread through the species. These traits may evolve even if they reduce survival ability. While natural selection adapts species to their environments, sexual selection shapes each sex in relation to the other sex. In The Origin, Darwin argued that sexual selection depends "not on a struggle for existence in relation to other organic beings or to external conditions, but on a struggle between the individuals of one sex, generally the males, for the possession of the other sex. The result is not death to the unsuccessful competitor, but few or no offspring."
Darwin didn't know about genes or DNA. But he understood that in a sexually reproducing species, the only way to pass a trait from one generation to the next was, by definition, through sexual reproduction. If an animal doesn't have sex, its heritable traits will die with it, and it will leave no hereditary trace in the next generation. As far as evolution is concerned, the animal may as well have died in infancy. Survival without reproduction means evolutionary oblivion. On the other hand, reproduction followed by death can still translate into evolutionary success. Sexual inheritance puts sexual reproduction at the heart of evolution. The concept of sexual selection is simply a way of describing how differences in reproductive success lead to evolutionary change.
Sexual, Natural, Artificial
To explain sexual selection, Darwin used the familiar metaphor of artificial selection. Victorian England was still mostly agricultural and pastoral. People knew about artificial selection, in which farmers domesticate plants and animals by allowing some individuals to breed and others not. Darwin had already used this barnyard type of artificial selection as a metaphor to explain how natural selection worked. Sexual
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