Love Dalén, Anders Götherström and colleagues have an interesting short article available in advance view in Molecular Biology and Evolution. The article argues, on the basis of Neandertal mtDNA data, for a distinction between Western and Eastern Neandertals, with the former group suffering a population collapse prior to the arrival of anatomically modern Homo sapiens.
One evolutionary scenario that could explain the genetic data and would be consistent with the simulation results would be an initial divergence between neandertal populations in Eastern and Western Europe ca. 55-70 kyr ago (Fig. S2, Table S3) followed by an extinction of western neandertals throughout most of their range and a subsequent recolonisation of the region either from the east or from a small refugium in the western part of their distribution
This idea is consistent with a project that I am working on, but I think could also be predicted on the basis of demographic reconstruction of Neandertals and other early human groups. A paper by Rachel Caspari and Sang-Hee Lee several years ago made the rather striking observation that older adults do not begin appearing in the fossil record in large numbers until near the end of the Pleistocene. I’ve gone work examining the feasibility of their data and observations with real demographic models, and they seem to hold up. It is likely that human populations prior to the last 20-30,000 years walked a real demographic tightrope, with fertility just keeping up with relatively early adult mortality and extended childhood development. Given this demographic background and the limits of Paleolithic technology to manipulate environmental factors, human population collapses were probably a hallmark of human evolutionary history. The interesting question is when, how geographically widespread, and to what extent these collapses may have occurred. I think there likely was a European Neandertal collapse, but it was most likely one of many such events that have shaped the evolutionary trajectory of humans.
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1. Dalon, L., L. Orlando, et al. (2012). “Partial genetic turnover in neandertals: continuity in the east and population replacement in the west.” Molecular Biology and Evolution. doi:10.1093/molbev/mss074
2. Caspari, R. and S.-H. Lee (2004). “Older age becomes common late in human evolution.” Proceedings of the National Academy of Sciences of the United States of America 101(30): 10895-10900. doi:10.1073/pnas.0402857101
