Crows are members of a widely distributed genus of birds, Corvus, in the family Corvidae. Ranging in size from the relatively small pigeon-size jackdaws (Eurasian and Daurian) to the Common Raven of the Holarctic region and Thick-billed Raven of the highlands of Ethiopia, the 40 or so members of this genus occur on all temperate continents except South America, and several islands.
In Europe, the word "crow" is used to refer to the Carrion Crow or the Hooded Crow, while in North America it is used for the American Crow or the Northwestern Crow. The crow genus makes up a third of the species in the Corvidae family. Crows appear to have evolved in Asia from the corvid stock, which had evolved in Australia. The collective name for a group of crows is a flock or a murder.
Recent research has found some crow species capable of not only tool use but also tool construction and meta-tool use. Crows are now considered to be among the world's most intelligent animals with an encephalization quotient approaching that of some apes. The Jackdaw and the European Magpie have been found to have a nidopallium approximately the same relative size as the functionally equivalent neocortex in chimpanzees and humans, and significantly larger than is found in the gibbon.
Crows are believed to have evolved in central Asia and radiated out into North America, Africa, Europe, and Australia. The latest evidence regarding the crow's evolution indicates descent within the Australasian family Corvidae. However, the branch that would produce the modern groups such as jays, magpies and large predominantly black Corvus had left Australasia and were concentrated in Asia by the time the Corvus evolved.
Corvus has since re-entered Australia (relatively recently) and produced five species with one recognized sub-species. The genus was originally described by Linnaeus in his 18th-century work Systema Naturae. The name is derived from the Latin corvus meaning "raven". The type species is the Common Raven (Corvus corax); others named in the same work include the Carrion Crow (C. corone), the Hooded Crow (C. cornix), the Rook (C. frugilegus), and the Jackdaw (C. monedula).