Evolution and dispersal of mammoths across the Northern Hemisphere.

Mammoths provide a detailed example of species origins and dispersal, but understanding has been impeded by taxonomic confusion, especially in North America. The Columbian mammoth Mammuthus columbi was thought to have evolved in North America from a more primitive Eurasian immigrant. The earliest American mammoths (1.5 million years ago), however, resemble the advanced Eurasian M. trogontherii that crossed the Bering land bridge around that time, giving rise directly to M. columbi. Woolly mammoth M. primigenius later evolved in Beringia and spread into Europe and North America, leading to a diversity of morphologies as it encountered endemic M. trogontherii and M. columbi, respectively. In North America, this included intermediates ("M. jeffersonii"), suggesting introgression of M. primigenius with M. columbi. The lineage illustrates the dynamic interplay of local adaptation, dispersal, and gene flow in the evolution of a widely distributed species complex.