While I generally agree with Glenn regarding the fossil record, readers have
to be very careful examining the evidence for hybridization as presented in
the PNAS paper.
As Tattersall and Schwartz note in a commentary in the same issue of PNAS (p
7117 - 7119) , many of the features that Duarte et al advocate as indicating
hybridism are in fact highly variable in H. sapiens and in H.
neanderthalensis - "there is nothing about the craniodental elements thus
far know and described that would be unusual for a Homo sapiens at this
young developmental age." As they note, this is a "brave and imaginative
interpretation of which it is unlikely that a majority of
paleoanthropologists will consider proven."
Sample sizes of one can tell us very little, particularly if the authors
want to extrapolate the results to indicate that hybridization had been
ongoing for serveral millennia (which they are forced to do, as they were
not able to argue that the specimen was a 50:50 [F1] hybrid). Until further
putative hybrids are found, it is best not to beleive that hybridization is
proven in any way.
Let's wait and see what happens ...
-jml