Transmissible cancer is a time capsule from the earliest dogs

These Alaskan malamutes share a common ancestor with an 11,000 year old tumor.

Flickr user RodBegbie

Innumerable cases of cancer arise each year throughout the animal kingdom. As far as we're aware, that cancer has only twice outlived the animal in which it originated by spreading to new hosts. One of these forms of cancer strikes the Tasmanian Devil and appears to have evolved within the last few hundred years. The second circulates among dogs, and its origin has been harder to pin down.

Now, researchers have sequenced the genomes of two cases that originated in Australia and Brazil and have shown that the cancer contains a mixture of markers. Some of them are from wolves and some are from domestic dogs, suggesting the cancer originated very close to the origin of dogs as a distinct population. Once established, the cancer circulated among a limited population of dogs for over 10,000 years before going global about 400 years ago.

We've actually known about the cancer since 1810, when the first report of it was published in London. It tends to be a sexually transmitted disease, causing large growths in the mouth or genital tract before the immune system gets it under control. Once controlled, the growths vanish and the dog remains immune for the rest of its life.