The Red Queen_ Sex and the Evolution of Human Nature - Matt Ridley [141]
The same is true of a chaffinch learning to sing. Unless it hears another chaffinch it never learns the species’s typical song. If it hears no chaffinch until it is fully grown, it never learns the right song, but produces a feeble half-song. Nor will it learn the song if it hears another chaffinch only when it is a few days old. Only if it hears a chaffinch during a critical period in between – from two weeks to two months of age – will it learn to sing correctly; after that period it never modifies its song by imitation.8
It is not hard to find examples of critical-period learning in people. Few people change their accents after the age of about twenty-five, even if they move from, say the United States to Britain. But if they move at fifteen, or ten, they quickly adopt a British accent. They are just like white-crowned sparrows, which sing with the dialect of the place where they lived at two months old.9 Likewise, children are remarkably good at picking up foreign languages just by exposure to them, whereas adults must laboriously learn them. We are not chicks or chaffinches, but we still have critical periods during which we acquire preferences and habits that are fairly hard to change.
This concept of the critical period is presumably what lies behind the Westermarck incest-avoiding instinct: we become sexually indifferent to those with whom we were reared during a critical period. Nobody is certain exactly what constitutes the critical period, but it is a plausible guess that it lasts from say eight to fourteen, the years before puberty. Common sense dictates that sexual orientation must be decided in such a fashion: a genetic predisposition meets examples during a critical period. Recall the fate of the baby chaffinch. For six weeks it is sensitive to learning chaffinch song. But during those six weeks of sensitivity, it hears all sorts of things: in my garden, cars, telephones, lawnmowers, thunder, crows, dogs, sparrows and starlings. Yet it only imitates the song of chaffinches. It has a predilection to learn chaffinch song (if it were thrush or a starling, it could indeed imitate some of the other things – one bird in Britain learnt the call of a telephone, causing havoc among garden sunbathers10). This is often the case with learning: ever since the work of Niko Tinbergen and Peter Marler in the 1960s, it has been well known that animals do not learn anything and everything; they learn what their brains ‘want’ to learn. Men are instinctively attracted to women, thanks to the interaction of their genes and hormones, but that tendency is much influenced, in a critical period, by role models, peer pressure and free will. There is learning, but there are predispositions.
A heterosexual man emerges from puberty with more than a general sexual preference for all women. He emerges with a distinct notion of beauty and ugliness. Some women ‘stun’ him; others he is indifferent to; still others he finds sexually repulsive. Is this, too, something that he acquired by a mixture of genes, hormones and social pressure? It must be, but the interesting question is, how much of each? If social pressure is everything, then the images and lessons we give to youths of both sexes, through films, books and advertisements and by example, are crucially important. If not, then the fact that men prefer, say, thin women, is fixed by the genes and hormones and not a passing fad.
Suppose you were a Martian, interested in studying people as William Thorpe studied chaffinches. You want to know how men learn their standards of beauty. So you keep boys in cages and some you expose to endless films of plump men admiring and being admired by plump women, while thin men and thin women are reviled. Others you keep in total ignorance of womanhood at all, so that the existence of women comes as a shock at the age of twenty.
It is revealing to speculate on what you think the outcome of the Martian’s experiment