Horse genetics, archaeology, and the beginning of riding.

Recent papers argued that the domestication of horses can be equated with the appearance of favorable genetic mutations that are first evident in individuals in the DOM2 clade dated about ∼2200-2100 BCE. We challenge the idea that this genetic shift alone defines domestication. Evidence from archaeology, ancient DNA, osteology, and other disciplines shows that horses from multiple genetic backgrounds (DOM1, DOM2, and, as we suggest here, DOM3) were managed, milked, and ridden long before 2200 BCE. Yamnaya groups (∼3200-2600 BCE) rode DOM2 horses-the direct ancestors of modern domestic stock-while incorporating them into diets, rituals, and mobility systems. Selection for traits linked to endurance and temperament began centuries earlier. Rather than a sudden breakthrough, domestication was a protracted, regionally varied process whose transformative effects on human mobility and social organization began as early as the fourth, if not the fifth millennium BCE, and set the stage for later DOM2 dominance.