Horses were first domesticated for riding and milking (yes, milking) 5500 years ago in northern Kazakhstan, but they’ve changed a lot since then. In a study published today in Science, researchers looked at genomes from 14 horses from between 4100 and 2300 years ago—the midpoint between when the animals were first domesticated and now—to better understand the arc of their domestication. The genomes came from 14 Bronze and Iron Age horses preserved as part of rituals in which sometimes dozens of horses were killed and elaborately arranged and buried by the Sintashta of Russia and Scythians of Kazakhstan. The samples revealed what these ancient societies were breeding for in their horses—sturdy legs and many different coat colors, for example. The genomes also showed a much greater genetic diversity in the ancient horse populations, suggesting that the limited diversity in the horse population of today came about during the last 2000 years and was not a result of domestication per se. More broadly, the research offers support for the “neural crest theory of domestication”—the idea that the pressure of domestication on genes acts at an early developmental stage on certain cells that later diversify and spread throughout the animal—allowing a suite of diverse traits like floppy ears and docile manner to be selected for all at once. Scientists suspect the same thing happened to dogs, cats, and a host of other domesticated animals.