Speciation reversal and the closing of the sapiens-Neanderthal divide.
A recent paper in Nature described how the collapse of an ecological niche, containing a species closely related to those in adjoining niches, could result in an interesting kind of double extinction (the term is used loosely here) as a consequence of both populations merging in the still viable eco-niche, interbreeding and producing a new hybrid species. While this particular paper spoke of varieties of lake fish, the situation with the discovery of Neanderthal genes in the modern human genome immediately jumped to mind.
For anyone interested, the paper I speak of is:
‘Eutrophication causes speciation reversal in whitefish adaptive radiations’ by Vonlanthen et al. in Nature volume 482, pages 357-363.
While there are many schools of thought on how this interbreeding took place, a common viewpoint is that Homos neanderthalensis and sapiens simply represented different radiations, and that the later (sapiens) simply displaced/absorbed the earlier (neanderthalensis) through either direct or indirect competition. The hybridisation of these species seems to have been treated by many workers as something that ‘just happened’ and really deserves greater thought. Could it be that climactic changes pressed Neanderthal populations into an overlap with their expansive ‘modern’ relatives? Who says that sapiens was the only population on the move? Additionally, if climate change had the result of reducing Neanderthal numbers then a shortage of mates may well have compounded this situaiton, drawing neanderthal populations closer to modern groups of out necessity. This could have fostered a situation of speciation reversal as described by Vonlanthen et al. with their lake fish. Worth thinking about, the person typing this article is, after all, a member of the resultant hybrid species.
Update: It seems that a recent paper has pressed the same viewpoint I was getting at above. I shall post on this shortly.