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From Dog to Dog

Some dogs living today harbor a legacy of another dog that lived about 6,000 years ago: a cancer developed by a dog living in Siberia at that time became transmissible and has been passed down to modern dogs living across the globe, Wired reports.

The University of Cambridge's Elizabeth Murchison and her colleagues have analyzed the exomes of nearly 550 canine transmissible venereal tumor collected from dogs around the world. As they report in Science, they used these samples to trace the founder dog back 4,000 to 8,500 years ago in Asia.

They also note that these tumors haven't been subject to same selective forces as human cancers, as GenomeWeb reports, which adds that neutral genetic drift appears to be the dominant force, rather than positive selection. Because of that, Discover's D-brief blog notes, random mutations accumulate in the tumors.

"The best strategy for this tumor turned out not to behave like a tumor at all, but like a parasite," first author Adrian Baez-Ortega from Cambridge tells Wired. "And since dogs don't seem to be affected by it much, you don't see the cancer trying to get better, because it's already good enough. If it does as little harm to the dogs as possible, it can survive indefinitely."