Monday, August 03, 2009

Homo floresiensis: An Early Split?

Debbie Argue of the Australian National University has published research suggesting that the remains consisting of Homo floresiensis diverged from the main hominin/hominid line as early as the early Pleistocene or late Pliocene, between 2 and 2.5 million years ago. The story, in ANU News, reports:

“Until now much of the debate about H. floresiensis has rested on analysis of the morphology and measurements of the remains found on the Indonesian island of Flores in 2004,” Ms Argue said. “Despite evidence supporting the idea that H. floresiensis constitutes a new species, some researchers continue to argue that it is the remains of a sick modern human or a near-human ancestor affected by island miniaturisation.”

To try to settle the debate, Ms Argue and her colleagues compared up to 60 characteristics from a range of early hominins, including H. erectus, and modern humans. They used two different computer-based modelling systems, testing relationships between the species to find the most parsimonious, or simplest, evolutionary line.

“Our cladistic analyses created two very similar evolutionary trees that establish a very early origin for H. floresiensis back around the emergence of the very first members of the Homo family. This suggests that H. floresiensis was not a sick modern human, not even a very close relative.

This, of course, assumes that the remains are not pathological, a position that has adherents. Recent studies have suggested that this is not the case, however. One has to be very careful in conducting cladistic analyses, which are trait driven, not morphologically driven. The specimen involved cannot have post-mortem deformation and the traits must be extremely clear. The article continues:
“The late survival of H. floresiensis on Flores could turn over the idea that H. sapiens was the only hominin around after the extinction of H. erectus and the Neanderthals,” Ms Argue said. “These two ideas represent paradigm shifts in the field of anthropology, forcing us to reconsider our long-held ideas about our species and its place in the world.”
If there was a second species running around after the transition from Homo erectus to Homo sapiens, it does raise questions about how many there might have been at other times. There is, for example, considerable morphological variation in Homo erectus in China, when compared to that of South East Asia and Africa. Whether this is suggestive of more than one species is not quite clear, though. If human evolutionary history is more like a bush than a tree, then this finding is in keeping with that idea. It is the same thinking that drove the idea to split Homo erectus into Homo erectus and Homo ergaster.

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