What natural blonds tell us about the power of pigment Much more has happened to the population of the Caribbean and its neighbours in the less distant past. Trinidad itself, with its small Native American population, was visited by Columbus and has been ruled by Spain, Britain, France and even, briefly, colonisers from what is now Latvia. Slaves and indentured labourers came from Africa and Asia. Now, like much of the continent, the island is a melting pot of their descendants. The Americas were empty until around 15,000 years ago, but human faeces from Oregon, newly dated to 14,300 years ago, are matched by remains from the same time from a campsite near the southern tip of Chile, suggesting the continent was filled quickly, probably by a small group who crossed the Bering land bridge from Siberia. Long afterwards came the Europeans and, within a decade of Columbus, the first African slaves. In the next three-and-a-half centuries, 12 million arrived from that continent - which meant four times as many people with black skins migrated in that period as did those with white. Nineteen out of 20 went to the Caribbean and South America. Sex started at once. Many of the Europeans who colonised the Caribbean married local women. Cortez impregnated a princess and, no doubt, many of his soldiers entered into informal engagements. From the first days of the European and African incursion, the imperatives of biology broke through social, religious and racial obstacles. Now, that history is being disentangled. In the five short centuries since the Europeans arrived, the New World has moved from being the most remote and most biologically diminished branch on the human family tree to its most diverse. The healing power of lust has brewed up a soup which has breached barriers of culture. Modern Colombia is the best microcosm of the great sexual interchange and of the overlap of biology with social identity. Nine tenths of its 50 million inhabitants identify themselves as of mixed ancestry, while most of the rest see themselves as displaced Africans and a tiny proportion claim to be Native American. Their genes reveal a mixture of DNA from three continents. As evidence of the power of pigment, the real proportion of genes of European origin in any dark-skinned individual is notably higher than the figure that emerges from asking them. People with dark skins over-estimate the extent of their African ancestry, which means that Colombians, like most others, place more importance on the small set of genes that determine the way they look than such minor players deserve. I ended my Trinidad talk on human difference by showing a picture of the mayor of London himself which, even 3,000 miles away, got a giggle of recognition. Why, I asked, had he and his fellows lost even more melanin than other Europeans? We can thank the warm waters around my audience's native island for that. The Gulf Stream brings their heat to our shores, which meant, thousands of years ago, that the first British farmers could grow primitive grains in the sunless climate. As a result, they could make even less vitamin D than their southern neighbours, and any new genes that further lightened their skin - and hair - were favoured. We owe Boris, with his boast of mixed English, German and Turkish ancestry, to the Caribbean; which may become a debating point when he stands again for Mayor of London - or for something else.