Horses are odd-toed ungulatemammals that have been widely domesticated by humans since about 4000 BC. Due to this long history of domestication, only one true species of wild horse remains with other wild horse breeds actually existing as feral colonies of once domesticated horses. A pack animal, horses roam in herds of mares (females) and foals (young horses) led by a stallion (a mature male). Having spent years with running as the primary form of defense for these herbivores, horses are able to walk and run shortly after being born. Horses have been bred and domesticated for many reasons over the years such as working, racing, and riding.