But that interpretation is belied by all the effort that women consciously put into decoration and surgical modification of their bodies so as to be attractive. In fact, men vary greatly in their genes, in the resources that they control, in their parenting qualities, and in their devotion to their wives. Although virtually any woman can get some man to marry her, only a few women can succeed in getting one of the few high-quality men, for whom women must compete intensely. Every woman knows that, even though some male scientists evidently don't.
A second objection notes that men in traditional societies had no opportunity to choose their spouse, whether on the basis of sexual ornamentation or any other quality. Instead, marriages were arranged by clan relatives, who did the choosing, often with the motive of cementing political alliances. In reality, though, bride prices in traditional societies, such as the New Guinea societies where I work, vary according to a woman's desirability, the woman's health and probable mothering qualities being important considerations. That is, although a bridegroom's views about his bride's sex appeal may be ignored, his relatives who actually select the bride do not ignore their own views. In addition, men certainly consider a woman's sex appeal in selecting partners for extramarital sex, which is likely to account for a higher proportion of babies in traditional societies (where husbands don't get to follow their sexual preferences in selecting their wives) than in modern societies. Furthermore, remarriage following divorce or the death of the first spouse is very common in traditional societies, and men in those societies have more freedom in selecting their second spouse.
The remaining objection notes that culturally influenced beauty standards vary with time, and that individual men within the same society differ in their tastes. Skinny women may be out this year but in next year, and some men prefer skinny women every year. However, that fact is no more than noise slightly complicating but not invalidating the main conclusion: that men at all places and times have on the average preferred well-nourished women with beautiful faces.
We have seen that several classes of human sexual signals-men's muscles, facial beauty, and women's body fat concentrated in certain places-apparently conform to the truth-in-advertising model. However, as I mentioned in discussing animals' signals, different signals may conform to different models. That's also true of humans. For example, the pubic and axillary hair that both men and women have evolved to grow in adolescence is a reliable but wholly arbitrary signal of attainment of reproductive maturity. Hair in those locations differs from muscles, beautiful faces, and body fat in that it carries no deeper message. It costs little to grow, and it makes no direct contribution to survival or to nursing babies. Poor nutrition may leave you with a scrawny body and disfigured face, but it rarely causes your pubic hair to fall out. Even weak ugly men and skinny ugly women sport axillary hair. Men's beards, body hair, and low-pitched voices as signals of adolescence, and men's and women's hair whitening as a signal of age, seem equally devoid of inner meaning. Like the red spot on a gull's bill and many other animal signals, these human signals are cheap and wholly arbitrary-many other signals can be imagined that would serve equally well.
Is there any human signal that exemplifies the operation of Fisher's runaway selection model or Zahavi's handicap principle? At first, we seem devoid of exaggerated signaling structures comparable to a widowbird's sixteen-inch tail. On reflection, however, I wonder whether we actually do sport one such structure: a man's penis. One might object that it serves a nonsignaling function and is nothing more than well-designed reproductive machinery. However, that is not a serious objection to my speculation: we have already seen that women's breasts simultaneously constitute signals and reproductive machinery. Comparisons with our ape relatives hint that the size of the human penis similarly exceeds bare functional requirements, and that that excess size may serve as a signal. The length of the erect penis is only about VA inches in gorillas and 1 1/2 inches in orangutans but 5 inches in humans, even though males of the two apes have much bigger bodies than men..
Are those extra couple of inches of the human penis a functionally unnecessary luxury? One counterinterpretation is that a large penis might somehow be useful in the wide variety of our copulatory positions compared to many other mammals. However, the 1 1/2-inch penis of the male orangutan permits it to perform in a variety of positions that rival ours, and to outperform us by executing all those positions while hanging from a tree. As for the possible utility of a large penis in sustaining prolonged intercourse, orangutans top us in that regard too (mean duration fifteen minutes, versus a mere four minutes for the average American man).
A hint that the large human penis serves as some sort of signal may be gained by watching what happens when men take the opportunity to design their own penises, rather than remaining content with their evolutionary legacy. Men in the highlands of New Guinea do that by enclosing the penis in a decorative sheath called a phallo-carp. The sheath is up to two feet long and four inches in diameter, often bright red or yellow in color, and variously decorated at the tip with fur, leaves, or a forked ornament. When I first encountered New Guinea men with phallo-carps, among the Ketengban tribe in the Star Mountains last year, I had already heard a lot about them and was curious to see how they were used and how people explained them. It turned out that men wore their phallocarps constantly, at least whenever I encountered them. Each man owns several models, varying in size, ornamentation, and angle of erection, and each day he selects a model to wear according to his mood, much as each morning we select a shirt to wear. In response to my question as to why they wore phallocarps, the Ketengbans replied that they felt naked and immodest without them. That answer surprised me, with my Western perspective, because the Ketengbans were otherwise completely naked and left even their testes exposed.
In effect, the phallocarp is a conspicuous erect pseudo-penis representing what a man would like to be endowed with. The size of the penis that we evolved was unfortunately limited by the length of a woman's vagina. A phallocarp shows us what the human penis would look like if it were not subject to that practical constraint. It is a signal even bolder than the widowbird's tail. The actual penis, while more modest than a phallocarp, is immodestly large by the standards of our ape ancestors, although the chimpanzee penis has also become enlarged over the inferred ancestral state and rivals men's penises in size. Penis evolution evidently illustrates the operation of runaway selection just as Fisher postulated. Starting from a 1/4-inch ancestral ape penis similar to the penis of a modern gorilla or orangutan, the human penis increased in length by a runaway process, conveying an advantage to its owner as an increasingly conspicuous signal of virility, until its length became limited by counterselection as difficulties fitting into a woman's vagina became imminent.
The human penis may also illustrate Zahavi's handicap model as a structure costly and detrimental to its owner. Granted, it is smaller and probably less costly than a peacock's tail. However, it is large enough that if the same quantity of tissue were instead devoted to extra cerebral cortex, that brainy redesigned man would gain a big advantage. Hence a large penis's cost should be regarded as a lost-opportunity cost: because any man's available biosyn-thetic energy is finite, the energy squandered on one structure comes at the expense of energy potentially available for another structure. In effect, a man is boasting, “I'm already so smart and superior that I don't need to devote more ounces of protoplasm to my brain, but I can instead afford the handicap of packing the ounces uselessly into my penis.”