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Go Milk a Fruit Bat!

Two of the memorably worst lines of English poetry, composed in 1799 by one John Hookham Frere:

The feather’d race with pinions skim the air—
Not so the mackerel, and still less the bear.

Hookham Frere’s insensitivity to bathos is impressive; but however inferior his verse it has a moral. The lines come from his unduly neglected poem The Progress of Man; Poetry of the Anti-Jacobin. Birds, bears, and fish carry a political message: Things are as they are and it is folly to change them. The French Revolution disturbed the God-given order: to proclaim the rights of man was as absurd as to suggest that mackerel—or even bears—might fly.

That logic is still with us. Nowadays, though, the status is quo because of evolution rather than the Almighty. Darwinism’s ability to explain the human condition was seized upon as soon as The Origin of Species appeared. From Plato to Galton, from Bernard Shaw to Charles Murray, biology has a dismal history of being used to absolve murderers, rapists, thieves, martyrs, saints, capitalists, Communists, and social democrats from blame for their actions.

Jared Diamond’s book sets out to evolutionize sex. It pins its heart (a metaphorical one in this case) to its sleeve in the very first paragraph. Sex, Diamond says, “…is the source of our most intense pleasures. Often it’s also the cause of misery, much of which arises from built-in conflicts between the evolved roles of women and men.”

So much, then, for the Arts Faculty; so simple the logic behind literature, painting, and the stage. Sex is, in addition, claims Diamond, responsible for the origin of hairlessness and tool making. It is all, it seems, a matter of evolved roles.

When it comes to the mating game, humans are unique. What causes women to be the only female mammals to conceal the time at which they are most fertile? Why, when it comes to penis size, does man stand alone? What is behind the human menopause, shared only with the pilot whale? Why, for that matter, is voyeurism not even commoner than the Internet allows? Other mammals do it in the road; and human sex is most peculiar in not being a social activity. We may share 98.8 percent of our genes with chimps and almost as many with gorillas; but when it comes to matters reproductive we are very different from either. The sex lives of most readers of The New York Review of Books are more similar (I assume) to those of albatrosses than of chimpanzees. Humans and sea birds both live in large colonies but show fidelity, albeit a grudging one, to a single mate. No other primate is remotely like that.

Diamond’s case is that our sex lives are better understood in terms of genetics than of grand opera. He is among the best of a talented bunch of writers on evolutionary biology. This book is (like his earlier work on the same theme, The Rise and Fall of the Third Chimpanzee) engaging and interesting to read. It is much more than—yet another—infantile attempt to use a string of unconnected anecdotes to explore the human spirit through the eyes of nature. Why Is Sex Fun? contains many strange and memorable tales of our sex lives and those of our relatives. It is guaranteed to keep a potential partner amused and amazed at the vagaries of what people—and animals—get up to when it comes to passing on their genes.

However, even Diamond falls into the trap that faces all who use Darwin to rationalize the human condition. No one denies that human behavior is constrained by our evolutionary past, in the sense that a pig’s ability to fly is limited by its ancestors’ lack of wings. It is fatally easy, though, to rework biology to fit a cultural idea; and by explaining everything to explain nothing.

The Origin was published only because Darwin received a letter containing the same notion from Alfred Russel Wallace. Their theory was presented to the Linnaean Society of London in 1858. It had rather little impact. The president (a dentist interested in reptiles) claimed that the year had not “been marked by any of those striking discoveries which at once revolutionize, so to speak, the department of science on which they bear; it is only at remote intervals that we can reasonably expect any sudden and brilliant innovation which shall produce a marked and permanent impression on the character of any brand of knowledge.”

That lack of judgment is reflected by the president’s own book, Kalygonomia, or the Laws of Female Beauty, an early contribution to the scientific study of sex. In those pre-Darwinian days, its main conclusion was to list “Defects in the intellectual system of Woman (4); Defects in the Mechanical system of Women (17) and Defects in the Vital system of Women (9).” The reptilian dentist had, alas, failed to notice the alibi which the society’s two speakers were to provide all possible theories of human sexuality. His work is forgotten.

Evolution is to allegory as statues are to birdshit. It is a convenient platform upon which to deposit badly digested ideas. Darwin saw where the importance of his theory really lay (“species are not—it is like confessing a murder—immutable”). He was much opposed to its naive use in human affairs. Darwinism has, though, been debased since it began by those who use it to support one creed or another. The problem goes far beyond sex. F.R. Leavis derided “the culture of the Sunday papers.” There is a modern counterpart. It is the culture of Scientific American: using a nodding acquaintance with evolution to promote an ethical agenda.

Diamond himself is far too good a biologist to fall into the trap of making science serve only as fuel for metaphor, although his book will no doubt be hijacked by those who do. Before accepting his arguments about the origins of human sex, though, it is worth remembering how dangerously accommodating evolutionary theory can be.

Alfred Russel Wallace became a socialist. He saw what natural selection’s message really was:

All shall contribute their share either of physical or mental labour, and…every one shall obtain the full and equal reward for their work. The future progress of the race will be rendered certain by the fuller development of its higher nature acted on by a special form of selection which will then come into play.

Herbert Spencer, Darwin’s amanuensis and inventor of that unfortunate phrase “the survival of the fittest,” came to a different conclusion. His notion of Social Darwinism was used to justify the excesses of capitalism. One of its proponents saw millionaires as “naturally selected in the crucible of competition.” The steel magnate Andrew Carnegie agreed. “Before Spencer,” he said, “all for me had been darkness, after him, became light—and right.”

According to Jared Diamond, Darwinism as light and right illuminates the secret crannies of human sexuality. He gives, for example, a giraffe’s-eye view of the child support laws. Males should, in any sensible mammal society, be off spreading their genes rather than squandering further efforts on an investment already made. Most are. What seems to us natural and decent, the nuclear family, would appear perverse to our relatives (let alone to the giraffe, whose long neck, according to the latest theory, is a product of males competing to impress females rather than stretching for the highest leaf). The family is as much a product of evolution as is a mandrill’s bottom: each is no more than a mechanism for ensuring the efficient transmittal of DNA. Men stay home only because human children—and the genes they contain—need two parents to have a good chance of surviving.

Evolution also explains why mothers are kinder to their babies than are fathers. It is only because they have already put so much into bearing them in the first place. Stepmothers are wicked for Mendelian reasons: they abuse their partner’s children because they are the vehicles of another woman’s genes.

All this is familiar enough. Evolution explains many strange patterns of animal behavior. Why should it not do the same for us? For a male spider who is going to meet—and have a chance to mate with—one female, it makes perfect sense to offer himself as a nuptial meal. It is all a matter of investment: feed your mate rather than start a hopeless search for another. When it comes to the human condition, as Diamond points out, a woman (however consumed by desire she might be) could not chew her way through enough of a man’s body at one sitting to make much difference to her baby’s survival. Perhaps, though, if men had only one chance for sex, post-copulatory cannibalism could catch on. Evolution has done stranger things.

As a professional biologist with a vast range of expertise, Jared Diamond is able to pull some startling skeletons out of the human sexual cupboard. Why, for example, is the milk of human kindness a product of only half the population? After all, men have nipples and the potential to use them. Males given certain chemicals to treat cancer lactate quite readily. Even a dose of heavy drinking can do the same thing as the liver loses its ability to suppress every man’s guilty secret, his circulating female hormones.

Women who have adopted a child (and who are not primed by pregnancy) can sometimes produce milk when suckled. Teenage boys, in a natural desire to see what might be done with their bodies, now and then take to stimulating their own nipples and (no doubt to their surprise) may succeed in doing the same. However, only the Dyak fruit bat goes to the logical conclusion. Males not only make milk but suckle their young. Given that men invest lots of care in their children (including earning enough to take them to McDonald’s), it is strange that they do not go the whole hog—or fruit bat—and produce food directly.

There is, as usual in biology, both an immediate and an ultimate explanation. The immediate reason why men have no milk has to do with DNA: males have the Y chromosome that is the switch that—just like those outside Paddington Station that with one tiny move command a train to go to Oxford or to Penzance—directs the embryo, within its first few hours, to develop as a male rather than a female. The Y carries one simple gene. The essence of maleness lies in its 240 DNA bases. All they do is increase the rate of growth of the early embryo, and by so doing to persuade it to make testes. From those simple orbs great consequences flow, among them pert but useless nipples.

Men—male mammals in general—have the potential to make milk but (pace the fruit bat) they do not. That is where evolution comes in. First, males in most species of mammal are crass enough to leave at fertilization rather than hang around for birth. Their energies are better invested in more sperm and more mates than in feeding the results of an earlier fling. There is simply no market for their milk.

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