FORGET trying to tell an Italian apart from a Spaniard by their looks. A collection of tiny differences in genetic make-up can locate a European far more effectively 鈥� even down to a single country.
By reading single-letter differences in the DNA of thousands of Europeans, two groups of researchers have shown independently that you can tell someone with a Finnish heritage from a Dane and distinguish those with German ancestry from the scions of England. The resulting genetic map mirrors Europe鈥檚 geographical map, right down to Italy鈥檚 boot.
鈥淚t tells us that geography matters,鈥� says John Novembre, a population geneticist at the University of California, Los Angeles, who led a study published in Nature (). Despite the migration and intermarriage that have taken place over the centuries, his team found that genetic differences between Europeans were almost entirely related to where they and their immediate ancestors were born.
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Apart from these myriad detailed differences, Europeans are genetically fairly uniform. 鈥淭he genetic diversity in Europe is very low,鈥� says Manfred Kayser, a geneticist at Erasmus University in Rotterdam, who led a second study, published in Current Biology ().
Both teams uncovered the detailed pattern only by analysing hundreds of thousands of DNA single-nucleotide polymorphisms (SNPs) 鈥� places in the genome where one person鈥檚 DNA might read A while another鈥檚 is T 鈥� across the genomes of people from some two dozen countries. The teams shared some of the same DNA samples. They noted the country of origin not only of each person but also of their parents and grandparents.
For each individual they analysed half a million SNPs, and then amalgamated the results mathematically to produce two numbers representing that person. This allowed each individual鈥檚 genome to be shown as a point on a two-dimensional plot: the bigger the differences in the genomes, the greater the distance between them on the plot.
In general, the closer two people鈥檚 geographical origins are, the more similar their DNA is. But when the researchers mapped thousands of genomes on a single plot, a striking pattern emerged. For example, Spanish and Portuguese genomes clustered 鈥渟outh-west鈥� of French genomes, while Italian genomes jutted 鈥渟outh-east鈥� of Swiss ones.
The pattern was so clear that when Novembre鈥檚 team placed a scaled geographical map over their genetic map, half the genomes landed within 310 kilometres of their country of origin, and 90 per cent within 700 kilometres.
Both teams found that southern Europeans boast more overall genetic diversity than Scandinavians, English and Irish. 鈥淭hat makes perfect sense with the major migration waves that went into Europe,鈥� says Kayser. He points out that in Homo sapiens鈥榮 European debut 35,000 years ago, expansions following the end of the ice age 20,000 years ago, and movements propelled by the advent of farming less than 10,000 years ago, members of established southern populations tended to strike north.
鈥淎 pattern in which genes mirror geography is essentially what you would expect from a history in which people moved slowly and mated mainly with their close neighbours,鈥� says Noah Rosenberg, a geneticist at the University of Michigan, Ann Arbor.
鈥淕enetic differences that match geography are what you expect when people moved slowly and bred with close neighbours鈥�
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