How Wolf Became Dog

When modern humans arrived in Europe perhaps 45,000 years ago, they encountered the gray wolf and other types of wolves, including the megafaunal wolf, which pursued large game such as mammoths. By that time wolves had already proved themselves among the most successful and adaptable species in the canid family, having spread across Eurasia to Japan and into the Middle East and North America. They were not confined to a single habitat type but flourished in tundra, steppelands, deserts, forests, coastal regions and the high altitude of the Tibetan Plateau. And they competed with the newly arrived humans for the same prey—mammoths, deer, aurochs, woolly rhinoceroses, antelopes and horses. In spite of this competition, one type of wolf, perhaps a descendant of a megafaunal wolf, apparently began living close to people. For many years scientists concurred on the basis of small portions of the genome that this species was the modern gray wolf (Canis lupus) and that this canid alone gave rise to dogs.

But last January geneticists discovered that this long-held “fact” was wrong. Repeated interbreeding between gray wolves and dogs, which share 99.9 percent of their DNA, had produced misleading signals in the earlier studies. Such consorting between the two species continues today: wolves with black coats received the gene for that color from a dog; shepherd dogs in Georgia's Caucasus Mountains mate so often with the local wolves that hybrid ancestors are found in both species' populations, and between 2 and 3 percent of the sampled animals are first-generation hybrids. (Building on the admixture theme, in June researchers writing in Current Biology reported on the sequencing of DNA from a 35,000-year-old wolf fossil from Siberia. This species appears to have contributed DNA to high-latitude dogs such as huskies through ancient interbreeding.)

Analyzing whole genomes of living dogs and wolves, last January's study revealed that today's Fidos are not the descendants of modern gray wolves. Instead the two species are sister taxa, descended from an unknown ancestor that has since gone extinct. “It was such a long-standing view that the gray wolf we know today was around for hundreds of thousands of years and that dogs derived from them,” says Robert Wayne, an evolutionary geneticist at the University of California, Los Angeles. “We're very surprised that they're not.” Wayne led the first genetic studies proposing the ancestor-descendant relationship between the two species and more recently was one of the 30 co-authors of the latest study, published in PLOS Genetics, that debunked that notion.

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