Donkey have worked together with humans for millennia. Traditionally, the scientific name for the donkey is "Equus asinus asinus" based on the principle of priority used for scientific names of animals. However, the International Commission on Zoological Nomenclature ruled in 2003 that if the domestic species and the wild species are considered subspecies of one another, the scientific name of the wild species has priority, even when that subspecies was described after the domestic subspecies. This means that the proper scientific name for the donkey is "Equus africanus asinus" when it is considered a subspecies, and "Equus asinus" when it is
Equus lambei horse, not an ass. The closest resemblance to "E." "lambei" is shown by the Mongolian horse, "E. caballus przewalskii", now believed to be extinct in the wild. In size and proportions, "E. lambei" resembles "E. caballus przewalskii". Among living horses, perhaps the Yukon horse most closely resembles the Przewalski's horse ("Equus caballus przewalskii") from Mongolia . The upper foot bones (metapodials) of "Equus lambei" are slender compared to Przewalski's horse. The bones of "E. lambei" also closely resemble the proximal phalanges of "E. caballus lenensis", an extinct species from the late Pleistocene of Siberia . Along with steppe bison ("Bison