European genetic twist

More evidence of genetic differences between the races:

The DeCode scientists found that the chromosome 17 inversion is rare in Africans, almost absent in Asians, but is possessed by 20 percent of Europeans, the same frequency as in Iceland. The inversion seems to have been favored by natural selection among Europeans in fairly recent times, perhaps the past 10,000 years.

"Maybe something switched it on in the European environment, such as an interaction with diet," said David Reich, a population geneticist at the Broad Institute.

Stefansson said that another property of the inversion, though one not described in the new Nature Genetics article, is that it is associated with longevity. DeCode scientists have located two sites on Icelanders' genomes where there is some genetic variant that promotes longer life span. The chromosome 17 inversion, it turns out, lies at one of these sites. It occurs at much higher frequency in women over 95 and in men over 90 than in the normal population. "It seems to confer on people the ability to live to extreme old age," Stefansson said.

It is particularly surprising that the same genetic element should promote fertility and longevity since most organisms are obliged to follow a strategy either of breeding fast during short lives or of living longer and having fewer children. "Usually people think of there being a trade-off between fertility and longevity," said Alan Rogers, a population geneticist at the University of Utah.

"So we are getting a free lunch here."

Fertility is doubtless affected by different genes in different populations and DeCode has found one special to Europeans because that is where it was looking. The increased frequency of the inversion in Europeans is one of a growing number of examples of recent human evolution.