EVIDENCE FOR 2 INDEPENDENT DOMESTICATIONS OF CATTLE

The origin and taxonomic status of domesticated cattle are controversi al. Zebu and taurine breeds are differentiated primarily by the presen ce or absence of a hump and have been recognized as separate species ( Bos indicus and Bos taurus). However, the most widely held view is tha t both types of cattle derive from a single domestication event 8000-1 0,000 years ago. We have examined mtDNA sequences from representatives of six European (taurine) breeds, three Indian (zebu) breeds, and fou r African (three zebu, one taurine) breeds. Similar levels of average sequence divergence were observed among animals within each of the maj or continental groups: 0.41% (European), 0.38% (African), and 0.42% (I ndian). However, the sequences fell into two very distinct geographic lineages that do not correspond with the taurine-zebu dichotomy: all E uropean and African breeds are in one lineage, and all Indian breeds a re in the other. There was little indication of breed clustering withi n either lineage. Application of a molecular clock suggests that the t wo major mtDNA clades diverged at least 200,000, and possibly as much as 1 million, years ago. This relatively large divergence is interpret ed most simply as evidence for two separate domestication events, pres umably of different subspecies of the aurochs, Bos primigenius. The cl ustering of all African zebu mtDNA sequences within the taurine lineag e is attributed to ancestral crossbreeding with the earlier B. taurus inhabitants of the continent.