I will have to follow up with my own comments later, but I wanted to direct you to Ken Weiss’s follow-up piece to his comments on the single-species hypothesis yesterday. I will make one brief observation, though. Ken writes:
But let’s try to sort credible evidence from religion here. In truth, if the evidence is being reliably interpreted, there does seem to have been some mixing and mingling (and mating) among lineages of our ancestors who had been long-separated since their common ancestry in Africa. This clearly shows that a strict multiple species view was wrong. But much hinges not on incisive insight but on definition–of what a ‘species’ is and the criteria by which species are declared.
The issue is a definitional one, part of what I was trying to convey yesterday, but it is not, I think, strictly a definitional issue. Whether or not Neandertals and expanding “modern” humans were the same species is a technical/definitional taxonomic question, but it is also a question about what evolutionary processes are important in shaping the pattern of biological variation and trajectory of recent human evolution. As such, the argument is not solely semantic, but also about the basic framework through which we test hypotheses in the Pleistocene. The null hypotheses under a “the Out of Africa model is mostly right” frame of reference and under a “there is something to that Multiregional model” are, in most instances, likely to be quite different. The issue over what names to apply to a given set of fossils may be technical, but the implication for how we reconstruct the important processes at play in our evolutionary past are not. Ken seems to suggest the same in his closing:
What remains interesting is the question I raised last time: the way in which the more modern creatures expanded out of Africa, and met and interacted with their less modern-looking brethren. And why the modern-lookers did, the evidence still seems to suggest, drive the others out of existence. That is the really important question, and it’s far more interesting than the DNA-based food fight.
