Via Yann a link to a new article by Erik Trinkaus suggesting that early modern humans in Europe cannot be simply explained as the result of an expansion of African modern humans but exhibit features that are not found in earliest African modern humans.
According to Trinkaus, the early modern Europeans exhibit features that are consistent with Neanderthal admixture. This is certainly the case, but that does not mean that the case of admixture is clear-cut: the earliest modern Africans are represented by less than a handful of specimens; moreover these are separated by 100ky at least from the earliest modern Europeans. Thus, neither the African population of origin, neither its evolutionary history up to the time of the African Exodus are well characterized.
It is possible that modern Out-of-Africans (whom I have called elsewhere Afrasians) were already different from the earliest anatomically modern Africans. We simply do not know much about them skeletally. Their main features are usually inferred by either (a) looking at early modern humans in Africa and seeing how they differ from previous Africans, or (b) looking at early modern humans in Eurasia and seeing how they are different from previous Eurasians and similar to each other. Both these approaches have led to a rather minimalist definition of modern humans; consequently, features that cannot be explained well under this definition are attributed to admixture.
As the genomic study of Neanderthals progresses, we should be able to find direct evidence for the introgression of Neanderthal genetic material into Homo sapiens. I suspect that such positive evidence (or negative evidence, assuming enough Neanderthal DNA is retrieved) would finally decide the question one way or another.
PNAS (Published online)
European early modern humans and the fate of the Neandertals
Abstract: A consideration of the morphological aspects of the earliest modern humans in Europe (more than 33,000 B.P.) and the subsequent Gravettian human remains indicates that they possess an anatomical pattern congruent with the autapomorphic (derived) morphology of the earliest (Middle Paleolithic) African modern humans. However, they exhibit a variable suite of features that are either distinctive Neandertal traits and/or plesiomorphic (ancestral) aspects that had been lost among the African Middle Paleolithic modern humans. These features include aspects of neurocranial shape, basicranial external morphology, mandibular ramal and symphyseal form, dental morphology and size, and anteroposterior dental proportions, as well as aspects of the clavicles, scapulae, metacarpals, and appendicular proportions. The ubiquitous and variable presence of these morphological features in the European earlier modern human samples can only be parsimoniously explained as a product of modest levels of assimilation of Neandertals into early modern human populations as the latter dispersed across Europe. This interpretation is in agreement with current analyses of recent and past human molecular data.