in what is now known as Mexico in only a few thousand years, starting between about 7,000 and 12,000 years ago, from still uncertain origins. In the light of this extraordinarily rapid rate of evolution, through (prehistoric) artificial selection, George C. Williams and others, have remarked that:

The question of evolutionary change in relation to available geological time is indeed a serious theoretical challenge, but the reasons are exactly the opposite of that inspired by most people's intuition. Organisms in general have not done nearly as much evolving as we should reasonably expect. Long term rates of change, even in lineages of unusual rapid evolution, are almost always far slower than they theoretically could be. The basis for such expectation is to be found most clearly in observed rates of evolution under artificial selection, along with the often high rates of change in environmental conditions that must imply rapid change in intensity and direction of selection in nature.