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 considered a species.