Tales from the DNA of domestic horses.

In our study of the origins of domestic horses, published in 1998, my colleagues and I examined sequence data of the mitochondrial DNA control region from 29 individuals, including Przewalski's horse and 14 domestic breeds (1). We found virtual genetic constancy within Przewalski's horse, unsurprising considering its severe historical bottlenecking, but a great deal of variation within and among domestic breeds. We wrote, “Overall, the amount of sequence divergence among modern breeds is greater than could have arisen within any plausible timescale of domestication (approximately 5,000 years by current archaeological estimates), and clearly reflects more ancient haplotype diversity.” We concluded, “The extent of modern haplotype diversity probably reflects an input of wild animals from different areas. It is unlikely that all domestic horses sprang from a single, local population. Domestic horses arose from wild stock distributed over a moderately extensive geographical region, large enough to have contained within it considerable pre-existing haplotype diversity.”