Analyses of 14 ancient horse genomes reveal the significant selective pressures domestication put on these animals, and highlight a relatively recent loss in their genetic diversity. Horse domestication likely started in the Kazakh steppe with the Botai culture roughly 5,500 thousand years ago. A lack of sufficiently preserved, ancient horse fossils has made it difficult to study genetic changes in the species since this pivotal moment. Here, Pablo Librado and colleagues examined the genomes of ancient domesticated horses, including a mare that lived about 4,100 years ago in modern day Chelyabinsk oblast, Russia; two stallions sacrificed at a burial site in Siberia about 2,700 years ago; and 11 stallions sacrificed at a site in Kazakhstan about 2,300 years ago. Their results reveal that selective pressure by breeders resulted in broader forelimbs, enriched development of carpal bones, and a variety of coat colors. A genetic mutation associated with muscle hypertrophy and short-distance sprint performance was also associated with horses selectively bred. Even humans' thirst for milk is evident in these ancient horse genomes, the authors report, as gene variants associated with increased lactation were detected among the animals (themselves a source of milk to humans, in some cases). Counter to the belief that domesticated horses may have been descendant from a small handful of stallions, the genomes analyzed in this study demonstrated great Y chromosomal diversity, suggesting that many stallions fathered the first domesticated horses. Lastly, based on their analysis, the authors suggest that the excess of deleterious mutations in present-day horses is likely not a consequence of early domestication, but of the last ~2,300 years of breeding.