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Evolutionary history and systematics

The members of the genus Corvus are believed to have evolved in Central Asia and radiated out from there into North America, Africa, Europe, and Australia. The center of diversity of Corvus is within Melanesia, Wallacea, and the island of New Guinea and surrounding islands, with numerous species endemic to islands in the area; other areas with a large number of crow species include South and Southeast Asia, East Africa, and Australia. A high density of endemics is also present in Mexico and the Caribbean.

The diversification of Corvus corresponded with a quick geographic expansion. The radiation of the genus resulted in rapid expansion of morphological diversity and fast speciation rates, especially around the beginning of the genus' radiation around 10 million years ago.

The genus was originally described by Carl Linnaeus in his 1758 10th edition of Systema Naturae. The name is derived from the Latin corvus meaning "raven". The type species is the common raven (Corvus corax); others named by Linnaeus in the same work include the carrion crow (C. corone), hooded crow (C. cornix), rook (C. frugilegus), and two species which have since been moved to other genera, the western jackdaw (now Coloeus monedula) and the Eurasian magpie (now Pica pica). At least 42 extant species are now considered to be members of Corvus, and at least 14 extinct species have been described.

The fossil record of crows is rather dense in Europe, but the relationships among most prehistoric species are not clear. Corvids are found in major cities across the world, and a major increase in the number of crows in urban settings has occurred since the 1900s. Historical records suggest that the population of American crows found in North America has been growing steadily since the introduction of European colonization, and spread east to west with the opening of the frontier. Crows were uncommon in the Pacific Northwest in the 1900s, except in riparian habitats. Populations in the west increased substantially from the late 1800s to the mid-1900s. Crows and ravens spread along with agriculture and urbanization into the western part of North America.