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Sexual Selection, and the Origin of Human Races
By: Jared Diamond
From: The Third Chimpanzee , Harper, 1992
J. Geffen
1. Racial variation has characterized humans for at least the past several thousand years, and possibly much longer. Already around 450 B.C., the Greek historian
Herodotus described the Pygmies of West Africa, the black-skinned Ethiopians, and a blue-eyed, red-haired tribe in Russia. Ancient paintings, mummies from Egypt and
Peru, and bodies of people preserved in European peat bogs confirm that people several thousand years ago differed in their hair and faces much as they do today.
Origins of modern races can be pushed back still further, to at least ten thousand years ago, since fossil skulls of that age from various parts of the world differ in many of the same respects that modern skulls from the same regions differ. More controversial are the studies of some anthropologists, contested by others, reporting continuity of racial skull characteristics for hundreds of thousands of years.
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Now let’s turn to the question whether natural selection or sexual selection has made the larger contribution to those visible geographic differences of ours. Take first the arguments about natural selection, the selection of traits that enhance survival. No scientist denies today that natural selection does account for many of the differences between species, like the fact that lions have paws with claws while we have grasping fingers. No one denies either that natural selection explains some geographic variation
(“racial variation”) within some animal species. For instance, Arctic weasels that live in areas covered by winter snow change color from brown in summer to white in winter, while more southerly weasels stay brown all year. That racial difference enhances survival, because white weasels against a brown background would be glaringly conspicuous to their prey but are camouflaged against snow.
3. By the same token, natural selection surely explains some geographic variation in humans. Many African blacks but no Swedes have the sickle-cell hemoglobin gene, because the gene protects against malaria, a tropical disease that would otherwise kill many Africans. Other localized human traits that surely evolved through natural selection include the big chests of Andean Indians (good for extracting oxygen from thin air at high altitudes), the compact shapes of Eskimos (good for conserving heat), the slender shapes of southern Sudanese (good for losing heat), and the slitlike eyes of north Asians (good for protecting eyes against cold and against sun glare off the snow). All these examples are easy to understand.
4. Can natural selection similarly explain the racial differences that we think of first, those in skin color and eye color and hair? If so, one might expect that the same trait (e.g., blue eyes) would reappear in different parts of the world with similar climates, and that scientists would agree on what the trait is good for.

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5. Seemingly the simplest trait to understand is skin color. Our skins run the spectrum from various shades of black, brown, copper, and yellowish to pink with or without freckles. The usual story to explain this variation by natural selection goes as follows. People from sunny Africa have blackish skins. So too (supposedly) do people from other sunny places, like southern India and New Guinea. Skins are said to get paler as one moves north or south from the equator, until one reaches northern
Europe, with the palest skins of all. Obviously, dark skins evolved in those people who were exposed to much sunlight. That’s just like the skins of whites tanning under the summer sun (or in tanning parlors!), except that tanning is a reversible response to sun rather than a permanent genetic one. It’s equally obvious what good a dark skin does in sunny areas: it protects against sunburn and skin cancer. Whites who spend lots of time outdoors in the sun tend to get skin cancer, and they get it on exposed parts of their body like their head and hands. Doesn’t that all make sense?
6. Unfortunately, it’s really not so simple at all. To begin with, skin cancer and sunburn cause little debilitation and few deaths. As agents of natural selection, they have an utterly trivial impact compared to infectious diseases of childhood. Many other theories have instead been proposed to explain the supposed pole-to-equator gradient in skin color.
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One favorite competing theory notes that the sun’s ultraviolet rays promote vitamin D formation in a layer of our skin beneath the main pigmented layer. Thus, people in sunny tropical areas might have evolved dark skin to protect them against the risk of kidney disease caused by too much vitamin D, while people in Scandinavia with its long, dark winters evolved pale skins to protect them against the risk of rickets caused by too little vitamin D. Two other popular theories: dark skins are to protect our internal organs against overheating by the tropical sun’s infrared rays; or – just the opposite – dark skins help keep tropical people warm when the temperature drops. And if those four theories aren’t enough for you, consider four more: that dark skins provide camouflage in the jungle, or that pale skins are less sensitive to frostbite, or that dark skins protect against beryllium poisoning in the tropics, or that pale skins cause deficiency of another vitamin (folic acid) in the tropics.
8. With at least eight theories in the running, we can hardly claim to understand why people from sunny climates have dark skins. That in itself doesn’t refute the idea that, somehow, natural selection caused the evolution of dark skins in sunny climates.
After all, dark skins could have multiple advantages, which scientists may sort out someday. Instead, the heaviest objection to any theory based on natural selection is that the association between dark skins and sunny climates is a very imperfect one.
Native peoples had very dark skins in some areas receiving relatively little sunlight, like Tasmania, while skin color is only medium in sunny areas of tropical Southeast
Asia. No American Indians have black skins, not even in the sunniest parts of the New
World. When one takes cloud cover into account, the world’s most dimly lit areas, receiving a daily average of under 3½ hours of sunlight, include parts of equatorial

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West Africa, South China, and Scandinavia, inhabited respectively by some of the world’s blackest, yellowest, and palest peoples! Among the Solomon Islands, all of which share a similar climate, jet-black people and lighter people replace each other over short distances. Evidently, sunlight has not been the sole selective factor that influences skin color.
9. The first response of anthropologists to these objections is to raise a counterobjection: the time factor. This argument tries to explain away the cases of pale- skinned people in the tropics by claiming that those particular peoples migrated to the tropics too recently to have evolved black skins. For example, the ancestors of
American Indians may have reached the New World only eleven thousand years ago: perhaps that hasn’t been long enough to evolve black skins in the tropical Americas.
But if you’re going to evoke the time factor to explain away objections to the climate theory of skin color, then you also have to consider the time factor for peoples who supposedly support that theory.
10. One of the prime supports of the climate theory is the pale skins of
Scandinavians, living in the cold, dark, foggy North. Unfortunately, Scandinavians have been in Scandinavia for an even shorter time than American Indians have been in the Amazon. Until about nine thousand years ago, Scandinavia was covered by an ice sheet and could hardly have supported any people, pale-skinned or dark-skinned.
Modern Scandinavians reached Scandinavia only around four or five thousand years ago, as a result of the expansion of farmers from the Near East and of Indo-European speakers from southern Russia. Either Scandinavians acquired their pale skins long ago in some other area with a different climate, or else they acquired them in
Scandinavia, within half the time that Indians have spent in the Amazon without becoming dark-skinned.
11. The sole people in the world about whom we can be certain that they spent the last ten thousand years in the same location were the natives of Tasmania. Lying south of Australia, at the temperate latitude of Chicago or Vladivostok, Tasmania used to be connected to Australia until it was cut off by rising sea level ten thousand years ago and became an island. Since modern Tasmanian natives didn’t have boats capable of going more than a few miles, we know that they were derived from colonists who walked out to Tasmania at the time of its connection to Australia, and who remained there continuously until they were exterminated by British colonists in the nineteenth century. If any people had enough time for natural selection to match their skin color to their local temperate-zone climate, it was the Tasmanians. Yet they had blackish skins, supposedly adapted to the equator.
12. If the case for natural selection of skin color seems weak, that for hair color and eye color is virtually nonexistent. There are no consistent correlations with climate, and not even any halfway-plausible theories for the supposed advantage lent by each color type. Blond hair is common in cold, wet, dimly lit Scandinavia and also among
Aborigines of the hot, dry, sunny desert of central Australia. What do those two areas

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155 have in common, and how does being blond help both Swedes and Aborigines to survive? Blue eyes are common in Scandinavia and supposedly help their owners see farther in dim, misty light. But that speculation is unproven, and all my friends in the even dimmer, mistier mountains of New Guinea see just fine with their dark eyes.
13. The racial traits for which it seems most absurd to seek an explanation based on natural selection are our variable genitalia and secondary sex characteristics. Are hemispherical breasts an adaptation to summer rainfall and conical breasts an adaptation to winter fog, or vice versa? Do the protruding labia minora of Bushman women protect them against pursuing lions, or reduce their water losses in the
Kalahari Desert? You surely don’t think that men with hairy chests can thereby keep warm while going shirtless in the Arctic, do you? If you do think so, then please explain why women don’t share hairy chests with men, since women also have to keep warm.
14. Facts such as these were what made Darwin despair of imputing human racial variation to his own concept of natural selection. He finally dismissed the attempt with a succinct statement: “Not one of the external differences between the races of man are of any direct or special service to him.” When Darwin came up with a theory that he preferred, he termed it “sexual selection” to contrast with natural selection, and he devoted an entire book to explaining it.
15. The basic notion behind this theory is easily grasped. Darwin noted many animal features that had no obvious survival value but that did play an obvious role in securing mates, either by attracting an individual of the opposite sex or by intimidating a rival of the same sex. Familiar examples are the tails of male peacocks, the manes of male lions, and the bright red buttocks of female baboons in estrus. If an individual male is especially successful at attracting females or intimidating rival males, that male will leave more descendants and will tend to pass on his genes and traits – as a result of sexual selection, not natural selection. The same argument applies to female traits as well.
16. For sexual selection to work, evolution must produce two changes simultaneously: one sex must evolve some trait, and the other sex must evolve in lockstep a liking for that trait. Female baboons could hardly afford to flash red buttocks if the sight revolted male baboons to the point of their becoming impotent.
As long as the female has it and the male likes it, sexual selection could lead to any arbitrary trait, just as long as it doesn’t impair survival too much. In fact, many traits produced by sexual selection do seem quite arbitrary. A visitor from Outer Space who had yet to see humans could have no way of predicting that men rather than women would have beards, that the beards would be on the face rather than above the navel, and that women would not have red and blue buttocks.
17. That sexual selection really can work was proved by an elegant experiment carried out by the Swedish biologist Malte Andersson on the long-tailed widowbird of
Africa. In this species the male’s tail in the breeding season grows to twenty inches

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195 long, while the female’s tail is only three inches. Some males are polygamous and acquire up to six mates, at the expense of other males who get none. Biologists had guessed that a long tail served as an arbitrary signal by which males attracted females to join their harem. Hence Andersson’s test was to cut off parts of the tails from nine males so that their tails were only six inches long. He then glued those cut segments to the tails of nine other males to give them thirty-inch tails, and he waited to see where the females built their nests. It turned out that the males with the artificially lengthened tails attracted on the average over four times as many mates as the males with artificially shortened tails.
18. Perhaps our first reaction to Andersson’s experiment is: Those dumb birds!
Imagine a female selecting a particular male to father her offspring merely because his tail is longer than other males’ tails! But before we get too smug, let’s consider again what we learned in the last chapter about how we humans select our own mates. Are our criteria such good indicators of genetic worth? Don’t some men and women set disproportionate value on the size or form of certain body parts, which are really nothing more than arbitrary signals for sexual selection? Why did we evolve to pay any attention at all to a beautiful face, which is useless to its owner in the struggle for survival?
19. In animals some of the traits that vary racially are ones produced by sexual selection. For instance, lions’ manes vary in length and in color. Similarly, snow geese occur in two color phases, a blue phase commoner in the western Arctic and a white phase commoner in the eastern Arctic. Birds of each phase prefer a mate of the same phase. Could human breast shape and skin color similarly be the outcome of sexual preferences that vary arbitrarily from area to area?
20. After 898 pages of his book Darwin convinced himself that the answer to this question was a resounding “yes.” He noted that we pay inordinate attention to breasts, hair, eyes, and skin color in selecting our mates and sex partners. He noted also that people in different parts of the world define beautiful breasts, hair, eyes, and skin by what is familiar to them. Thus, Fijians, Hottentots, and Swedes each grow up with their own learned, arbitrary beauty standards, which tend to maintain each population in conformity with those standards, since individuals deviating too far from the standards would find it harder to obtain a mate.
21. Darwin died before his theory could be tested against rigorous studies of how people actually do select their mates. Such studies have proliferated in recent decades, and I summarized the results in the preceding chapter. There I showed that people tend to marry individuals who resemble themselves in every conceivable character, including hair and eye and skin color. To explain that seeming narcissism of ours, I reasoned that we develop our beauty standards by imprinting on the people we see around us in childhood – especially on our parents and siblings, the people we see the most. But our parents and siblings are also the people to whom we bear the strongest physical resemblance, since we share their genes. Thus, if you’re a fair-skinned, blue-

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235 eyed blond who grew up in a family of fair-skinned blue-eyed blonds, that’s the sort of person whom you’ll consider most beautiful and will seek as a mate.
22. To test that imprinting theory of human mate choice rigorously, one would have to do experiments like shipping some Swedish babies to adoptive parents in New
Guinea, or painting some Swedish parents permanently black. Then, after waiting twenty years for the babies to grow up, one could study whether they preferred
Swedes or New Guineans as sex partners. Alas, once again, the Search for Truth about humans founders on practical problems. But such tests can be performed with full experimental rigor on animals.
23. Take snow geese, for example, with their blue and white color phases. Do white geese learn or inherit their preference in the wild for white geese over blue ones?
Canadian biologists hatched gosling eggs in an incubator, then put the goslings into a nest of goose “foster parents.” When those goslings grew up, they chose mates with the color of the foster parents. When goslings were reared in a large mixed flock of both blue and white birds, they showed no preference between blue and white prospective mates on reaching adulthood. Finally, when the biologists dyed some white parents pink, their offspring came to prefer pink-dyed geese. Thus, geese do not inherit but learn a color preference, by imprinting on their parents (and on their siblings and playmates).
24. How, then, do I think that people in different parts of the world evolved their differences? Our insides remained invisible to us and were molded only by natural selection, with such results as that tropical Africans but not Swedes got the antimalarial defense of the sickle-cell hemoglobin gene. Many visible features of our outsides also got molded by natural selection. But, just as in animals, sexual selection had a big effect in molding the external traits by which we pick our mates.
25. For us humans those traits are especially the skin, eyes, hair, breasts, and genitals. In each part of the world those traits evolved in lockstep with our imprinted aesthetic preferences to reach different, somewhat arbitrary end points. Which particular human population ended up with any given eye or hair color may have been partly an accident of what biologists term the “founder effect.” That is to say, if a few individuals colonize an empty land and their descendants then multiply to fill the land, the genes of those few founding individuals may still dominate the resulting population many generations later. Just as some birds of paradise ended up with yellow plumes and others with black plumes, so some human populations ended up with yellow hair and others with black hair, some with blue eyes and others with green eyes, some with orange nipples and others with brown nipples.
26. I don’t mean thereby to claim that climate has nothing whatsoever to do with skin color. I acknowledge that tropical peoples tend on the average to have darker skins than temperate-zone peoples, though there are many exceptions, and that this is probably due to natural selection, though we’re unsure of the exact mechanism.

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Instead, I’m saying that sexual selection has been strong enough to render the correlation between skin and color and sun exposure quite imperfect.
27. If you’re still skeptical about how traits and aesthetic preferences can evolve together to different arbitrary end points, just think about our changing fashion preferences. When I was a schoolboy in the early 1950s, women rated men with crew cuts and clean-shaven faces as handsome. Since then, we’ve seen a parade of men’s fashions, including beards, long hair, earrings, purple-dyed hair, and the Mohawk hair style. A man daring to flaunt any of those fashions in the 1950s would have revolted the girls and enjoyed zero mating success. That’s not because crew cuts were better adapted to the atmospheric conditions of Stalin’s last years, while a purple Mohawk has higher survival value in our post-Chernobyl era. Instead, men’s appearances and women’s tastes changed together, and the changes occurred far more rapidly that evolutionary changes in skin color, since no gene mutations were required. Either women came to like crew cuts because good men had them, or men adopted crew cuts because good women liked them, or something of both happened. The same goes for women’s appearances and men’s tastes.
28. To a zoologist, the visible geographic variability that sexual selection produced in humans is impressive. I’ve argued that much of our variability is a by-product of a distinctive feature of the human life cycle: our choosiness with respect to our spouses and sex partners. I don’t know of any other wild animal species in which eye color of different populations can be green, blue, gray, brown, or black, while skin color varies geographically from pale to black and hair is either red, yellow, brown, black, gray, or white. There may be no limits, except those imposed by evolutionary time, on the colors with which sexual selection can adorn us. If humanity survives another twenty thousand years, I predict that there will be women with naturally green hair and red eyes – and men who think such women are the sexiest.

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Answer in your own words in English, unless otherwise indicated .
Answer the question below in English .
1. What do the first five paragraphs tell us about the purpose of this study?
Answer : ____________________________________________________________
Answer the question below in Hebrew .
2. On what grounds does the author – paragraphs 5-8 – question the notion that natural selection accounts for variation in skin colour among humans?
Answer : ____________________________________________________________
Answer the question below in English .
3. In what connection and to what end are American Indians – paragraphs 8-9 – mentioned?
Answer : ____________________________________________________________
4. What common thesis do the Scandinavians – paragraph 10 – American Indians
– paragraph 8 – and Tasmanians – paragraph 11 – demonstrate? Elaborate.
Answer : ____________________________________________________________
Complete the sentence below .
5. The blond Scandinavians and the Aborigines of central Australia – paragraph 12
– are mentioned in order to show that _____________________________________
Complete the sentence below .
6. Since hairy chested males and hairless females live in the same climatic zones, it should be obvious that _______________________________________________

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Answer the question below in English .
7. What thesis do the red buttocks of female baboons, the manes of male lions, and the tails of male peacocks point to?
Answer : ____________________________________________________________
Answer the question below in Hebrew .
8.
Describe Andersson’s experiment – paragraph 17; what does it suggest?
Answer : ____________________________________________________________
9. What does the fact that humans like what they consider to be beautiful faces suggest in the terms of this study?
Answer : ____________________________________________________________
Answer the question below in English .
10. What facts about the evolution of the human species – paragraph 24 – would demonstrate the working of natural selection?
Answer : ____________________________________________________________
Answer the question below in Hebrew .
11. Discuss the main idea in this study.
Answer : ____________________________________________________________