The United States has the right amount of genetic diversity to buoy its economy, claim economists.

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The invalid assumption that correlation implies cause is probably among the two or three most serious and common errors of human reasoning. Evolutionary biologist Stephen Jay Gould was referring to purported links between genetics and an individuals intelligence when he made this familiar complaint in his 1981 book The Mismeasure of Man.

Fast-forward three decades, and leading geneticists and anthropologists are levelling a similar charge at economics researchers who claim that a countrys genetic diversity can predict the success of its economy. To critics, the economists paperseems to suggest that a countrys poverty could be the result of its citizens genetic make-up, and the paper is attracting charges of genetic determinism, and even racism. But the economists say that they have been misunderstood, and are merely using genetics as a proxy for other factors that can drive an economy, such as history and culture. The debate holds cautionary lessons for a nascent field that blends genetics with economics, sometimes called genoeconomics. The work could have real-world pay-offs, such as helping policy-makers to set the right level of immigration to boost the economy, says Enrico Spolaore, an economist at Tufts University near Boston, Massachusetts, who has also used global genetic-diversity data in his research.

But the economists at the forefront of this field clearly need to be prepared for harsh scrutiny of their techniques and conclusions. At the centre of the storm is a 107-page paper by Oded Galor of Brown University in Providence, Rhode Island, and Quamrul Ashraf of Williams College in Williamstown, Massachusetts1. It has been peer-reviewed by economists and biologists, and will soon appear in American Economic Review, one of the most prestigious economics journals.

The paper argues that there are strong links between estimates of genetic diversity for 145countries and per-capita incomes, even after accounting for myriad factors such as economic-based migration. High genetic diversity in a countrys population is linked with greater innovation, the paper says, because diverse populations have a greater range of cognitive abilities and styles. By contrast, low genetic diversity tends to produce societies with greater interpersonal trust, because there are fewer differences between populations. Countries with intermediate levels of diversity, such as the United States, balance these factors and have the most productive economies as a result, the economists conclude.

The manuscript had been circulating on the Internet for more than two years, garnering little attention outside economics until last month, when Science published a summary of the paper in its section on new research in other journals. This sparked a sharp response from a long list of prominent scientists, including geneticist David Reich of Harvard Medical School in Boston, Massachusetts, and Harvard University palaeoanthropologist Daniel Lieberman in Cambridge.

In an open letter, the group said that it is worried about the political implications of the economists work: the suggestion that an ideal level of genetic variation could foster economic growth and could even be engineered has the potential to be misused with frightening consequences to justify indefensible practices such as ethnic cleansing or genocide, it said.

Our study is not about a nature or nurture debate.

The critics add that the economists made blunders such as treating the genetic diversity of different countries as independent data, when they are intrinsically linked by human migration and shared history. Its a misuse of data, says Reich, which undermines the papers main conclusions. The populations of East Asian countries share a common genetic history, and cultural practicesbut the former is not necessarily responsible for the latter. Such haphazard methods and erroneous assumptions of statistical independence could equally find a genetic cause for the use of chopsticks, the critics wrote.

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Economics and genetics meet in uneasy union