Update II: John Hawks leaves a comment.
Update: Kambiz has much more comment.
… Here we use a variety of statistical tests founded on explicit predictions from quantitative- and population-genetic theory to show that genetic drift can explain cranial differences between Neandertals and modern humans. These tests are based on thirty-seven standard cranial measurements from a sample of 2524 modern humans from 30 populations and 20 Neandertal fossils. As a further test, we compare our results for modern human cranial measurements with those for a genetic dataset consisting of 377 microsatellites typed for a sample of 1056 modern humans from 52 populations. We conclude that rather than requiring special adaptive accounts, Neandertal and modern human crania may simply represent two outcomes from a vast space of random evolutionary possibilities.
I am generally skeptical of drift as a catchall explanation (it often serves as a deus ex machina, just as sexual selection has become), but from what little I have gleaned from paleoanthropology it seems that some workers contend that the morphological differences between Neandertals and “modern” humans are overemphasized. I’m thinking here body form, e.g., the short & stocky build typical of Arctic peoples. Obviously the consistent patterns of changes in size and proportion of large mammalian species (larger & stockier the further north) across many taxa point to common selective pressures due to environment; but what about cranium? I simply don’t know. I do know that human bone structure and teeth have become less robust over the last 10,000 years, perhaps due to agriculture. This might simply be relaxing the selection for more robust physiques. I hope John takes a minute from his grant application and comments….