The donkey is a domesticated equine. It derives from the African wild ass, Equus africanus, and may be classified either as a subspecies thereof, Equus africanus asinus, or as a separate species, Equus asinus. It was domesticated in Africa some 5,000 years ago, and has been used mainly as a working animal since that time. There are more than 40 million donkeys in the world, mostly in underdeveloped countries, where they are used principally as draught or pack animals. While working donkeys are often associated with those living at or below subsistence, small numbers of donkeys or asses are kept for breeding or as pets in developed countries. An adult male donkey is a jack or jackass, an adult female is a jenny or jennet, and an immature donkey of either sex is a foal. Jacks are often mated with female horses (mares) to produce mules; the less common hybrid of a male horse (stallion) and jenny is a hinny. Traditionally, the scientific name for the donkey is Equus asinus asinus, on the basis of the principle of priority used for scientific names of animals. However, the International Commission on Zoological Nomenclature ruled in 2003 that if the domestic and the wild species are considered subspecies of a common species, 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. At one time, the synonym ass was the more common term for the donkey. The first recorded use of donkey was in either 1784 or 1785. While the word ass has cognates in most other Indo-European languages, donkey is an etymologically obscure word for which no credible cognate has been identified. Hypotheses on its derivation include the following: perhaps from Spanish for its don-like gravity; the donkey was also known as "the King of Spain's trumpeter". perhaps a diminutive of dun (dull grayish-brown), a typical donkey colour.