Red deer are ruminants, characterized by a four-chambered stomach. Genetic evidence indicates that the red deer, as traditionally defined, is a species group, rather than a single species, though exactly how many species the group includes remains disputed. The closely related and slightly larger American elk or wapiti, native to North America and eastern parts of Asia, had been regarded as a subspecies of red deer, but recently it has been established as a distinct species. The ancestor of all red deer, including wapiti, probably originated in central Asia and resembled sika deer.