By:Alan S. Miller Ph.D., Satoshi Kanazawa Ph.D.

Human nature is one of those things that everybody talks about but no one can define precisely. Every time we fall in love, fight with our spouse, get upset about the influx of immigrants into our country, or go to church, we are, in part, behaving as a human animal with our own unique evolved nature—human nature.

This means two things. First, our thoughts, feelings, and behavior are produced not only by our individual experiences and environment in our own lifetime but also by what happened to our ancestors millions of years ago. Second, our thoughts, feelings, and behavior are shared, to a large extent, by all men or women, despite seemingly large cultural differences.

Human behavior is a product both of our innate human nature and of our individual experience and environment. In this article, however, we emphasize biological influences on human behavior, because most social scientists explain human behavior as if evolution stops at the neck and as if our behavior is a product almost entirely of environment and socialization. In contrast, evolutionary psychologists see human nature as a collection of psychological adaptations that often operate beneath conscious thinking to solve problems of survival and reproduction by predisposing us to think or feel in certain ways. Our preference for sweets and fats is an evolved psychological mechanism. We do not consciously choose to like sweets and fats; they just taste good to us.
The implications of some of the ideas in this article may seem immoral, contrary to our ideals, or offensive. We state them because they are true, supported by documented scientific evidence. Like it or not, human nature is simply not politically correct.

Adapted from Why Beautiful People Have More Daughters, by Alan S. Miller and Satoshi Kanazawa, to be published by Perigee in September 2007.

1. Men like blond bombshells (and women want to look like them)

Long before TV—in 15th- and 16th- century Italy, and possibly two millennia ago—women were dying their hair blond. A recent study shows that in Iran, where exposure to Western media and culture is limited, women are actually more concerned with their body image, and want to lose more weight, than their American counterparts. It is difficult to ascribe the preferences and desires of women in 15th-century Italy and 21st-century Iran to socialization by media.

Women’s desire to look like Barbie—young with small waist, large breasts, long blond hair, and blue eyes—is a direct, realistic, and sensible response to the desire of men to mate with women who look like her. There is evolutionary logic behind each of these features.

Men prefer young women in part because they tend to be healthier than older women. One accurate indicator of health is physical attractiveness; another is hair. Healthy women have lustrous, shiny hair, whereas the hair of sickly people loses its luster. Because hair grows slowly, shoulder-length hair reveals several years of a woman’s health status.

Men also have a universal preference for women with a low waist-to-hip ratio. They are healthier and more fertile than other women; they have an easier time conceiving a child and do so at earlier ages because they have larger amounts of essential reproductive hormones. Thus men are unconsciously seeking healthier and more fertile women when they seek women with small waists.

Until very recently, it was a mystery to evolutionary psychology why men prefer women with large breasts, since the size of a woman’s breasts has no relationship to her ability to lactate. But Harvard anthropologist Frank Marlowe contends that larger, and hence heavier, breasts sag more conspicuously with age than do smaller breasts. Thus they make it easier for men to judge a woman’s age (and her reproductive value) by sight—suggesting why men find women with large breasts more attractive.

Alternatively, men may prefer women with large breasts for the same reason they prefer women with small waists. A new study of Polish women shows that women with large breasts and tight waists have the greatest fecundity, indicated by their levels of two reproductive hormones (estradiol and progesterone).

Blond hair is unique in that it changes dramatically with age. Typically, young girls with light blond hair become women with brown hair. Thus, men who prefer to mate with blond women are unconsciously attempting to mate with younger (and hence, on average, healthier and more fecund) women. It is no coincidence that blond hair evolved in Scandinavia and northern Europe, probably as an alternative means for women to advertise their youth, as their bodies were concealed under heavy clothing.

Women with blue eyes should not be any different from those with green or brown eyes. Yet preference for blue eyes seems both universal and undeniable—in males as well as females. One explanation is that the human pupil dilates when an individual is exposed to something that she likes. For instance, the pupils of women and infants (but not men) spontaneously dilate when they see babies. Pupil dilation is an honest indicator of interest and attraction. And the size of the pupil is easiest to determine in blue eyes. Blue-eyed people are considered attractive as potential mates because it is easiest to determine whether they are interested in us or not.

The irony is that none of the above is true any longer. Through face-lifts, wigs, liposuction, surgical breast augmentation, hair dye, and color contact lenses, any woman, regardless of age, can have many of the key features that define ideal female beauty. And men fall for them. Men can cognitively understand that many blond women with firm, large breasts are not actually 15 years old, but they still find them attractive because their evolved psychological mechanisms are fooled by modern inventions that did not exist in the ancestral environment.

2. Humans are naturally polygamous

The history of western civilization aside, humans are naturally polygamous. Polyandry (a marriage of one woman to many men) is very rare, but polygyny (the marriage of one man to many women) is widely practiced in human societies, even though Judeo-Christian traditions hold that monogamy is the only natural form of marriage. We know that humans have been polygynous throughout most of history because men are taller than women.

Among primate and nonprimate species, the degree of polygyny highly correlates with the degree to which males of a species are larger than females. The more polygynous the species, the greater the size disparity between the sexes. Typically, human males are 10 percent taller and 20 percent heavier than females. This suggests that, throughout history, humans have been mildly polygynous.

Relative to monogamy, polygyny creates greater fitness variance (the distance between the “winners” and the “losers” in the reproductive game) among males than among females because it allows a few males to monopolize all the females in the group. The greater fitness variance among males creates greater pressure for men to compete with each other for mates. Only big and tall males can win mating opportunities. Among pair-bonding species like humans, in which males and females stay together to raise their children, females also prefer to mate with big and tall males because they can provide better physical protection against predators and other males.

In societies where rich men are much richer than poor men, women (and their children) are better off sharing the few wealthy men; one-half, one-quarter, or even one-tenth of a wealthy man is still better than an entire poor man. As George Bernard Shaw puts it, “The maternal instinct leads a woman to prefer a tenth share in a first-rate man to the exclusive possession of a third-rate one.” Despite the fact that humans are naturally polygynous, most industrial societies are monogamous because men tend to be more or less equal in their resources compared with their ancestors in medieval times. (Inequality tends to increase as society advances in complexity from hunter-gatherer to advanced agrarian societies. Industrialization tends to decrease the level of inequality.)

3. Most women benefit from polygyny, while most men benefit from monogamy

When there is resource inequality among men—the case in every human society—most women benefit from polygyny: women can share a wealthy man. Under monogamy, they are stuck with marrying a poorer man.

The only exceptions are extremely desirable women. Under monogamy, they can monopolize the wealthiest men; under polygyny, they must share the men with other, less desirable women. However, the situation is exactly opposite for men. Monogamy guarantees that every man can find a wife. True, less desirable men can marry only less desirable women, but that’s much better than not marrying anyone at all.

Men in monogamous societies imagine they would be better off under polygyny. What they don’t realize is that, for most men who are not extremely desirable, polygyny means no wife at all, or, if they are lucky, a wife who is much less desirable than one they could get under monogamy.

Copyright belongs to Psychology Today.