Domestication did horses no genetic favors

Horses have paid a genetic price for becoming human companions, a study of ancient equine DNA suggests. Modern domestic horses have more harmful genetic variants than ancient wild breeds did, researchers have found.

Domesticated horses have no living ancestors, so Ludovic Orlando of the University of Copenhagen and colleagues sequenced the genomes of a 16,000-year-old and a 43,000-year-old horse, both excavated near Krasnoyarsk, Russia. Those ancient horses lived before horses were domesticated. They are not direct ancestors of today’s horses; instead, the horses were on a branch in the equine family tree separate from the ancestors of domesticated breeds and of wild Przewalski’s horses, Orlando and colleagues report December 15 in the Proceedings of the National Academy of Sciences.

Comparing genetic variants from modern horse breeds with the ancient horses, the researchers found that some of traits that make for winning thoroughbreds have been around for tens of thousands of years.

In general, though, domestic horses have more harmful genetic variants than the 43,000-year-old horse did. The buildup in detrimental DNA is not simply due to inbreeding, the researchers found. Instead it is the cost of domestication, in which humans have overridden natural selection by picking animals with desirable traits (as people see them) and unwittingly chosen damaged genes.