DESPITE our best attempts to work out when people first brought dogs to heel, it appears that man鈥檚 best friend it still giving us the runaround.
Peter Savolainen and his team at the Royal Institution of Technology in Stockholm carried out a major genetic analysis of more than 650 domestic dogs. They found that all dogs are descended from just a few grey wolves that roamed east Asia some 15,000 years ago.
But Robert Wayne of the University of California at Los Angeles, who has used a similar technique to show that early humans first took domestic dogs to the New World only a few thousand years later, disagrees. His findings imply that dogs could have been domesticated tens of thousands of years earlier, about 40,000 years ago.
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Dogs are generally thought to have evolved from grey wolves (Canis lupus) living near ancient human settlements. Archaeologists date the oldest evidence of dogs to a 14,000-year-old jawbone found in Germany, and some 12,000-year-old bones from Israel. On the face of it, that suggests that dogs, like farm animals, were first domesticated in south-western Asia.
By analysing mitochondrial DNA sequences, Savolainen鈥檚 team has now shown that modern dogs belong to five distinct genetic groups, the largest of which is most closely related to wolves found in east Asia. Although that in itself is not enough to pinpoint where dogs were first domesticated, this group also shows the greatest genetic diversity, suggesting they have been separated from wolves the longest, says Savolainen.
Extrapolating backwards, he concluded that variations of gene sequences among the most common dog group imply they all came from five or fewer founder females that lived 15,000 years ago. These founder wolves also shared a common female ancestor about 40,000 years ago.
This could indicate that domestication began then, but Savolainen doubts it. A closer look shows that descendants of some of the founder wolves diversified much more quickly than their ancestors, suggesting that this is when people began artificially selecting for certain traits (Science, vol 298, p 1610).
But Wayne remains unconvinced. The data suggests a much more ancient divergence about 40,000 years ago, he told New Scientist.
Wayne鈥檚 study shows that Native Americans first brought dogs to the Americas some 12,000 to 14,000 years ago. The animals were already genetically diverse, and DNA from their bones shows that they originated in Eurasia. Wayne argues that a few thousand years is not enough time for cultures to have passed domestic dogs through Asia and into America, or for the dogs themselves to have gained such diverse genetic sequences (Science, vol 298, p 1613).