A family tree in every gene

TLDR: The prestigious journal Nature Genetics devoted a large supplement to the question of whether human races exist and, if so, what they mean, and some geneticists offered their views.

Abstract: Shortly after last year’s tsunami devastated the lands on the Indian Ocean, The Times of India ran an article with this headline: ‘Tsunami may have rendered threatened tribes extinct’. The tribes in question were the Onge, Jarawa, Great Andamanese and Sentinelese – all living on the Andaman Islands and they numbered some 400 people in all. The article, noting that several of the archipelago’s islands were low-lying, in the direct path of the wave, and that casualties were expected to be high, said, ‘Some beads may have just gone missing from the Emerald Necklace of India’. The metaphor is as colorful as it is well intentioned. But what exactly does it mean? After all, in a catastrophe that cost more than 150,000 lives, why should the survival of a few hundred tribal people have any special claim on our attention? There are several possible answers to this question. The people of the Andamans have a unique way of life. True, their material culture does not extend beyond a few simple tools, and their visual art is confined to a few geometrical motifs, but they are hunter-gatherers and so a rarity in the modern world. Linguists, too, find them interesting since they collectively speak three languages seemingly unrelated to any others. But The Times of India took a slightly different tack. These tribes are special, it said, because they are of ‘Negrito racial stocks’ that are ‘remnants of the oldest human populations of Asia and Australia’. It’s an old-fashioned, even Victorian, sentiment. Who speaks of ‘racial stocks’ anymore? After all, to do so would be to speak of something that many scientists and scholars say does not exist. If modern anthropologists mention the concept of race, it is invariably only to warn against and dismiss it. Likewise many geneticists. ‘Race is a social concept, not a scientific one’, according to Dr Craig Venter – and he should know, since he was first to sequence the human genome. The idea that human races are only social constructs has been the consensus for at least 30 years. But now, perhaps, that is about to change. Last fall, the prestigious journal Nature Genetics devoted a large supplement to the question of whether human races exist and, if so, what they mean. The journal did this in part because various American health agencies are making race an important part of their policies to best protect the public – often over the protests of scientists. In the supplement, some two dozen geneticists offered their views. Beneath the jargon, cautious phrases and academic courtesies, one thing was clear: the consensus about social constructs was unraveling. Some even argued that, looked at the right way, genetic data show that races clearly do exist. The notion that human races do not exist can be dated to 1972. This is when Richard Lewontin, a Harvard geneticist, wrote an influential review showing that most human genetic variation can be found within any given ‘race’ (Lewontin 1972). If one looked at genes rather than faces, he claimed, the difference between an African and a European would be scarcely greater than the difference between any two Europeans. A few years later he wrote that the continued popularity of race as an idea was an ‘indication of the power of socioeconomically based ideology over the supposed objectivity of knowledge’ (Lewontin 1974). Most scientists are thoughtful, liberal-minded and socially aware people. It was just what they wanted to hear. Three decades later, it seems that Dr Lewontin’s facts were correct, and have been abundantly confirmed by ever better techniques of detecting genetic variety (e.g. Barbujani et al. 1997). His reasoning, however, was wrong. His error was an elementary one, but such was the appeal of his argument that it was only a couple of years ago that a Cambridge University statistician, A. W. F. Edwards, put his finger on it (Edwards 2003). The error is easily illustrated. If one were asked to judge the ancestry of 100 New Yorkers, one could look at the colour of their skin. That would do much to single out the Europeans, but little to distinguish the Senegalese from the Solomon Islanders. The same is true for any other feature of our bodies. The shapes of our eyes, noses and skulls; the colour of our eyes and our hair; the heaviness, height and hairiness of our bodies are all, individually, poor guides to ancestry. But this is not true when the features are taken together. Certain skin colours tend to go with certain kinds of eyes, noses, skulls and bodies. When we glance at a stranger’s face we use those associations to infer what continent, or even what country, he or his ancestors came from – and we usually get it right. To put it more abstractly, human physical variation is correlated; and correlations contain information. INVITED EDITORIAL