Social Structure that Allowed (and Even Encouraged) Domestication of the Horse
Horses are highly social animals which, when left to their own devices (for example, as mustangs in the American west are), form herds including one intact male (stallion) with a small group of females and their offspring. These groups generally consist of no more than 10 adult animals and are always seen together. This same pattern is seen in the domestic horse’s closest wild relative, Przewalski’s horse, and is also seen in other wild equids, including some species of zebras. Females (mares) generally have one foal at a time, which usually remains with the group until it reaches puberty, when it is driven off by the dominant male or chooses to leave (in the case of young stallions), or is stolen by another stallion from another band (in the case of young females). Young males often form bachelor bands, groups in which they remain until they are mature enough to acquire their own females. Horses are neither loud nor aggressive animals and generally never move faster than a walk, unless approached by a predator (Houpt, 2005; Moehlman, 2004).
Horses are non-ruminant herbivores, which means that, while they consume a very high-fiber plant diet, they do not ferment that plant matter in a rumen, but rather accomplish forage fermentation in the cecum, a blind-ended hindgut digestive organ located between the small intestine and the cecum. The low-calorie nature of their diets has caused horses, like other grazers, to evolve to spend the vast majority of their time grasping, chewing, and swallowing forage and then walking to another patch of forage (Hintz, 2005).
Domestication had huge advantages for horses as individuals and as a species. Horses were originally domesticated from a relatively large group of mares and a relatively small group of stallions, perhaps one single foundation sire. He was probably a low-ranking individual in the wild and wouldn’t have been able to fight stronger, higher-ranking individuals and mate with females. By associating with humans, he was able to breed with the mares that humans had in captivity—whatever kind of captivity that was (Anthony, 2007).