According to Jared Diamond, author of “Guns, Germs & Steel” (1997), the races of mankind were shaped more by sexual selection – who we choose to have sex with – than by natural selection – the forces of nature determining how we look. Darwin said the same.
Take skin colour, for example. It seems like a straightforward case of natural selection: light skin is favoured in places with a weak sun to prevent rickets, while dark skin is favoured in the tropics to prevent skin cancer.
That makes sense, but it is not quite that simple – for two reasons:
- Almost no one dies of skin cancer young enough to affect having children. So it does not affect natural selection.
- The amount of sunlight a place receives does not quite match up with skin colour. The general pattern holds but there are plenty of places where the two do not fit, like Tasmania, the Amazon or parts of Africa.
For things like eye colour and hair the match-up is even worse. Why do people in Europe, for example, have blue eyes but nowhere else? The conditions in Europe are not that strange.
Diamond says that physical attraction, what we like physically in a mate, messes things up. Nature matters but sex does too: To have children you must not only live long enough in good health, you must also be desirable to the opposite sex.
That is why women have large breasts, for example: not because babies need it, but because it turns men on and helps to create the babies in the first place.
But what determines what turns men on? Is it something they are born with? Diamond says no: it comes from who you grew up with. We know that from studies done on birds: if a bird is raised by a different race, it will tend to mate with that race even when given a chance to mate with its own race.
It is not just birds. Diamond notices the same thing among Chinese American women: those who grew up among whites tend to marry white even when given a fair chance to marry Chinese. Likewise, those who grew up in Chinese neighbourhoods tend to marry Chinese American husbands even when given a reasonable chance to marry white.
Partly it is from the forces of nature, but mostly it is from the founder effect: humans spread across the earth in little bands. When a band settled in a new land, the genes of that band would have a huge effect on those who came after for thousands of years. That is why blonde hair is native to Europe but also to Australia. It was not because of the sun or anything, but because a few people in the bands that settled those places turned out to have blonde hair.