The name Corvidae for the family was introduced by the English zoologist William Elford Leach in a guide to the contents of the British Museum published in 1820. Over the years, much disagreement has arisen on the exact evolutionary relationships of the corvid family and their relatives. What eventually seemed clear was that corvids are derived from Australasian ancestors and from there spread throughout the world. Other lineages derived from these ancestors evolved into ecologically diverse, but often Australasian, groups. In the late 1970s and throughout the 1980s, Sibley and Ahlquist united the corvids with other taxa in the Corvida, based on DNA–DNA hybridization. The presumed corvid relatives included currawongs, birds of paradise, whipbirds, quail-thrushes, whistlers, monarch flycatchers and drongos, shrikes, vireos, and vangas, but current research favors the theory that this grouping is partly artificial. The corvids constitute the core group of the Corvoidea, together with their closest relatives (the birds of paradise, Australian mud-nesters, and shrikes). They are also the core group of the Corvida, which includes the related groups, such as Old World orioles and vireos.