Bad news for the objectively anti-Neanderthal and anti-Denisovan bigots and others concerned about genetic variation among populations in the deep south of Georgia: some early hominid "species" may not be different species after all:
Early, diverse fossils — those currently recognized as coming from distinct species like Homo habilis, Homo erectus and others — may actually represent variation among members of a single, evolving lineage. In other words: just as people look different from one another today, so did early hominids look different from one another, and the dissimilarity of the bones they left behind may have fooled scientists into thinking they came from different species. (source: NYTimes)
The idea is that Homo habilis, Homo rudolfensis and Homo erectus are not branches but variation within the single trunk. Further, the degree of variation among the skulls from Georgia– all evidently from a single population– is similar to, or greater than, the degree of variation among skulls from Africa. This suggests that speciation has been overprojected for Africa, too. Finally, the differences between the Georgian and African fossils are similar to the differences among the Georgian fossils. So speciation relative to migration may have been overprojected:
Naturally, some scholars affirm and some dissent. A lot of bones to pick!
[Fred Spoor from University College London] added that the very specific characteristics that had been used to define H.erectus, H.habilis and H.rudolfensis "were not captured by the landmarks that they used".
"They did not consider that the thick and protruding brow ridges, the angular back of the braincase and some details of the base of the cranium are derived features for H.erectus, and not present in H.habilisand H.rudolfensis."
Chris Stringer at the Natural History Museum in London said that the team had made an excellent case "that this remarkable new skull, with its huge jawbone", was part of the natural variation of the Dmanisi population.
But he said he was doubtful that all of the early Homo fossils can be "lumped into an evolving H.erectus lineage".
So the dispute is over which features different among the samples are sufficient to assert speciation, and which count as natural variation within a single species. Seems like we'll need more fossils before that issue can be resolved definitively. The site in Dmanisi may well provide them!
Update: interesting, slightly different coverage from WSJ: http://online.wsj.com/news/articles/SB10001424052702304384104579141600675336982