Homo Mysterious: Evolutionary Puzzles of Human Nature (12 page)

The “competition avoidance” hypothesis argues that menopause is how middle-aged women avoid competing with younger women—by opting out altogether.
²²
Once again, they need not be doing so out of genuine altruism, since those younger women who benefit are typically either the menopausal woman’s daughters or daughters-in-law, so that in either case, the woman whose ovaries say “no” may well be saying “yes” to her genes, each of which is likely, with a probability of .25, to be present in her grandchildren.

According to the grandmother hypothesis, among the payoffs received by grandmothers themselves are benefits that go beyond emotional gratification and satisfied love and that include evolutionary payoffs received by the menopausal woman’s genes. Taking a “gene’s eye” view of evolution, natural selection does not proceed with the individual in mind, but rather, the gene. As biologist Richard Dawkins has pointed out so cogently, bodies aren’t the bottom line in evolution; genes are.
²³
Bodies don’t last beyond a single generation; genes do. And so, when at a certain age women forego reproducing (i.e., when they commence menopause) and also begin being helpful grandmothers, their genes are “selfishly” looking out for copies of themselves, genes “for” menopause that get projected into the future via those additional grandchildren that are benefited.

Sarah Hrdy tells of a particular langur monkey, “old Sol,” who had ceased cycling and thus might have been quasimenopausal, in a sense. She was obviously decrepit and marginalized within her group, living a sad, solitary, and—it appeared—increasingly useless end of life until a strange adult male invaded the langur troop and attempted to work infanticidal mayhem. Writes Hrdy,

It was Sol who repeatedly charged this sharp-toothed male nearly twice her weight to place herself between him and the threatened baby. When the infanticidal male seized the infant in his jaws and ran off with him, Sol pursued the attacker and wrested the wounded baby back. With danger momentarily past, and the wounded infant once again in his mother’s arms, old Sol resumed her diffident attitude. That an arthritic old female would become marginalized with age is
scarcely surprising. More curious was Sol’s transformation from decrepit outcast to intrepid defender.
²⁴

It doesn’t diminish Sol’s courage to point out that by defending youngsters, some of whom may be her own grandchildren, Sol and other warrior grandmothers may literally be justifying their own postreproductive existence, or—to put it differently—their genes are acting out their own payoff.

Even then, the grandmother hypothesis is not literally proven. It seems likely, however, that menopause may serve to keep middle-aged women from reproducing at a time when their personal risk is increasing (higher mortality) and payoff is decreasing (greater danger of producing genetically defective offspring), so that these women are more fit in the evolutionary sense if they care for those children already produced (prudent mothering) as well as contributing to their own successful grandmotherhood. Even women who have no children would presumably be influenced by the same basic evolutionary pressures, since for most of our species’ history, intentional childlessness was not an option. In addition, once our conceptual focus has shifted to what is presumably natural selection’s focus as well—the gene rather than the individual—it isn’t strictly necessary for someone to have children to receive an evolutionary benefit.

Biologists refer increasingly to “inclusive fitness” as the real focus of evolution. This differs from simple Darwinian fitness in that it includes somewhat more: not just the production of successful offspring, but the enhanced success of copies of one’s constituent genes as represented in all genetic relatives, with the importance of each relative devalued as he or she is more distantly related—which is to say, as the probability declines that these individuals share genes by common descent. By this accounting, children are important, but so are nieces, nephews, grandchildren, cousins, and so forth. As a result, we can see how by maximizing an individual’s inclusive fitness, natural selection could have favored older individuals contributing to their genes’ eventual success whenever they contributed to their network of genetic relatives.

Even a childless, postmenopausal woman could therefore enhance the long-term success of her genes by contributing to them in the bodies of her various relatives, among whom grandchildren are likely to loom large, but not exclusively. In many pre-literate societies, elderly individuals contribute to their fellow group members (many of them genetic relatives) by serving as a source of useful information, especially in times of crisis: where to find water during a once-in-a-lifetime drought, how to prepare certain food for long-term storage, what to do with troublesome tribe members. In such cases, it might not matter that the person in question is unable to get pregnant, since she is already a repository of potentially life-saving and gene-promoting wisdom.

In today’s rapidly changing technological world, in which youngsters are needed to translate their grandparents’ email, program their cell phones, and unravel the mysteries of iPods and MP3s, it sometimes seems like information and assistance largely flows from the young to the old. But historically, and to a large extent even now, the elderly have been priceless sources of trans-generational wisdom, something far more precious than mere technique. As a result, this gives us reason to ask whether human beings
ever
become truly postreproductive, insofar as, this side of the grave, they can contribute—not merely to the lives of their offspring, but also to others within their long, inclusive reach.

It may even be that such “selfish beneficence” on the part of the elderly—or, if you prefer, their genes—has enabled our species to luxuriate in prolonged childhood, which in turn is intimately connected to our having evolved such large brains. So if you like being human—which is to say, being smart—thank grandma!

There are also “manly mysteries,” but for some reason, these aren’t as sexy or prominent as their womanly counterparts. Here, therefore, is yet another mystery, a recursive one insofar that it is a mystery about mysteries: Why are there so many sex-related womanly mysteries and, comparatively speaking, so few male ones? And why are the manly mysteries so trivial by contrast?

Among those pallid male enigmas are: Why are men so much hairier than women? Furthermore, why is this hirsuteness distributed as it is, especially prominent on the face (beard and mustache) and, to a lesser extent chest, the arms and legs? And given that men are generally more hairy than women—whatever the reason—why is this difference reversed on top of the head? For all their hairiness, why are men so much more prone to go bald? It is well known that testosterone is intimately involved here, along with genetics, but this doesn’t explain why the outcome—which presumably has been favored by natural selection—is what it is. “Male pattern baldness,” for example, is a description, not an explanation.

Most evolutionary biologists would likely suspect that the answer has something to do with social signaling, but exactly what? It doesn’t seem that there has even been any interesting speculation. Yet.

There are some other mysteries that aren’t really “male.” Rather, they exist in the context of comparing male with female, men with women. And they aren’t so much “sexual” as they emerge along a dimension contrasting the two sexes. For starters, many animals are “sexually dimorphic,” which means that males and females are easily distinguished, and not simply by their genitals. In such cases, males are almost inevitably the gaudy, fancy sex while females are relatively dowdy and unprepossessing. Among human beings, this situation is reversed: It is the women not the men who are especially concerned with their looks and who characteristically adorn their bodies with all manner of bright, showy, attention-grabbing accoutrements.

Earlier, seeking an evolutionary basis for one aspect of female “anatomical ornamentation” (conspicuous nonlactating breasts), we discussed the “sexy son” hypothesis along with the handicap principle. In that case, we looked at male choice of females, itself an inversion of the far more common phenomenon in the animal world: female choice of males. It is this process of female choice that appears responsible for the evolution of traditionally elaborate male secondary sexual characteristics such as feathers, wattles, horns and antlers, manes, ruffs, and so forth.

To be sure, even in modern Western societies, men invest in their dress and appearance, but women outdo them by an order of
magnitude, sporting the equivalent of a peacock’s tail, only one that is constructed culturally rather than anatomically.

Unlike, say, the case of woodland warblers in which males are brightly colored jewels while females are for the most part drab and distressingly difficult to tell apart, looking strictly at the anatomical endowment of naked men and women, it isn’t obvious which sex is fancier. At the same time there is no question that if we admit the role of local culture and technology, women are fancy and men, plain. There is also no question that the matter of female adornment is the “least biological” of all those traits we shall be considering in
Homo Mysterious
. Moreover, as befits something that is so strongly influenced by local cultural traditions, there are exceptions: Among certain New Guinea societies, for example, men adorn themselves with pig tusks and bird-of-paradise plumes, and among many Australian and African aboriginal people, men, not women, are elaborately painted for most ceremonies.

But the pattern nonetheless holds, and is quite robust, especially in the West and in societies influenced by occidental culture: Just consider the comparative expenditure on female versus male cosmetics—nail polish, lipstick, eye liner, hair care products of all description
versus
aftershave cologne, or the female rainbow of brightly colored dresses, shoes, handbags, jewelry, and other accessories
versus
the visually tedious sameness of “men in suits.” Fancy females are pretty much a cross-cultural universal,
²⁵
with women being consistently more decorated; this calls for explanation, especially because an evolutionary perspective suggests that the cosmetics and fashion industries did not
create
a demand for female ornamentation so much as
respond
to it.

Not unlikely, this demand on the part of women derives from the adaptive value—to themselves—of creating demand (for themselves) on the part of men. Mammals are unusual in that females are specifically adapted to nourish their offspring via breast milk. As a result, paternal care is rare among our mammalian relatives. But human beings are exceptional mammals in that—because of our prolonged juvenile dependency—males have quite a bit to contribute. Consequently, unlike most animals, in which female choice is the rule, the evolution of
Homo sapiens
has placed a premium on women making themselves attractive to males as well, thereby giving them an advantage when it comes to mating with
males who may be especially able to invest in them and their offspring.

In this regard, it is of more than passing significance that around the world, women are drawn to cultural practices and technology such as breast enhancement, lipstick, hair and skin products, and clothing that “flatters the figure,” all of which exaggerate traits characteristic of healthy youth, with its subliminal promise of reproductive potential. Women, in short, are trying to make themselves more attractive—no surprise here, except when we consider that this basic pattern goes contrary to the typical situation among most animals, in which males especially “try” to be attractive, which means, of course, that natural selection has particularly favored those that do so.

There is a deeper underlying pattern here, one that is found in other species and is entirely consistent with women’s “artificial” ornamentation in our own: The sex investing more tends to be the one doing most of the choosing. This is essentially because the greater the investment on offer, the greater the eagerness to gain sexual access to such individuals, and this eagerness by one sex (in most animals, the males) provides leverage to the other (in most animals, the females). As the more heavily investing sex, females therefore typically have the opportunity to choose among males, who seek to be among the chosen. Human beings do not quite reverse this “differential investment,” since their eggs, pregnancy, and subsequent lactation
ⁱⁱ
induce women nearly always to invest more in their offspring than do men. But to a degree highly unusual among mammals, men too invest in their offspring, which sets up the potential for them to be choosy as well.

An interesting parallel is offered by the unfortunately named “Mormon crickets,” which are neither crickets nor devotees of the Church of Latter Day Saints. They’re actually katydids, and are among the few species in which males invest more heavily in offspring than do females, since male Mormon crickets produce a large, nutrient-rich spermatophore, which is transferred to the female at mating. As a result, in this species males are sexually reticent and choosy, whereas females are pushy and self-advertising, a
reversal of the traditional male–female pattern. In the case of Mormon crickets, females display their desirability by literally climbing on the backs of males, who prefer to mate with those that are heaviest (indicating they have the most eggs).
²⁶

It is possible that early proto-hominid men preferentially chose women who, like egg-laden female Mormon crickets, were somewhat rotund. These days, however, women are more likely to use clothing, cosmetics, and so forth to display and enhance their desirability. They aren’t merely choosy, as befits females of pretty much any species, but they also seek to be chosen. And toward this end, they use adornment, creams, emollients, hair-dos and don’ts, eye shadow, lipstick, rouge, powder, nail polish, depilatories, and eye-catching dresses, tights, bracelets, necklaces, and earrings.