Horses have paid a genetic price for becoming human companions, a study of ancient equine DNA, by M. Schubert et al, suggests. Modern domestic horses have more harmful genetic variants than ancient wild breeds did, the researchers found. Breeding has led to these more harmful variants in equine DNA
Domesticated horses carrying damaged DNA
A comparison of ancient and modern horse genomes has found that thousands of years of serving as human companions has led to damaged DNA in domesticated horses.
© 2015 by Science News
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 todayâs horses; instead, the horses were on a branch in the equine family tree separate from the ancestors of domesticated breeds and of wild Przewalskiâs horses, Orlando and colleagues report December 15 in the Proceedings of the National Academy of Sciences.
The domestication of the horse revolutionized warfare, trade, and the exchange of people and ideas. This long process, which ultimately transformed wild horses into the hundreds of breeds living today, is difficult to reconstruct from archeological data and modern genetics alone.
Two complete horse genomes were sequenced, predating domestication by thousands of years, to characterize the genetic footprint of domestication.
These ancient genomes reveal predomestic population structure and a significant fraction of genetic variation shared with the domestic breeds but absent from Przewalskiâs horses. Positive selection on genes involved in various aspects of locomotion, physiology, and cognition were found.
Finally, the evidence showed that modern horse genomes contain an excess of deleterious mutations, likely representing the genetic cost of domestication.
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 have unwittingly chosen damaged genes.
M. Schubert et al. Prehistoric genomes reveal the genetic foundation and cost of horse domestication. Proceedings of the National Academy of Sciences.