If you are in the San Francisco area and interested in human evolution, you should stop by our session at the AAAs this afternoon. There is a great group of panelists who have agreed to contribute and I am excited to see how all of the talks fit together in the session. Here is a draft of my talk (link to dropbox).
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My paper will begin with a brief discussion of the problem presented by a lack of appropriate comparative models for questions in paleoanthropology. I will then suggest that Neandertals, rather than being a problem in need of explanation by paleoanthropology, represent one of the best available comparative lenses through which to view human evolutionary processes in the Pleistocene. The active production of genetic knowledge relating Neandertals and living and recent human populations, in particular, poses challenges to the commonly held view of Neandertals as a reproductively-isolated biological species, distinct from living humans and our immediate ancestors.
The hypothesis that I am interested in is whether other recognized Pleistocene taxa exceed the variation present in a combined Neandertal/fossil human sample. In addition to developing a multivariate characterization of the variability of this sample, I look at how that variation is patterned across time and space within the sample. I then apply these data to a much larger sample of Pleistocene specimens (143 in total), including fossils traditionally designated as Homo erectus, Homo heidelbergensis, Homo habilis, Australopithecus robustus, Au. boisei and Au. africanus (H. florisiensis and Au. sediba, too, but the samples are obviously limited for those comps). A couple of interesting results come out using the human-Neandertal variation as a guide. First, while temporal displacement only explains a very small amount of the variation in the human-Neandertal sample, it provides a very good prediction of the morphological divergence between the other well-sampled Homo lineages (e.g. erectus and heidelbergensis) and humans and Neandertals. In contrast, the well-sampled Australopithecine lineages fall well outside this prediction. In fact, while the average pairwise morphological difference between the well-sampled Homo lineages fails to achieve significance using a Neandertal-modern human critical value, all of the Australopithecus/Homo comparisons are significant. The remains from Flores and Malapa are also distinctive, though the limited sample of available data makes the comparisons more problematic. In other words, if you use the Neandertal-human comparison as a threshold value, basically outlining the limits of morphological/temporal divergence, the results support only a small number of hominin lineages in the Pleistocene, smaller than most traditional views hold.
Finally, I interrogate the theoretical basis of using a Neandertal-human perspective a little more. First, I point out that while time had only a small impact on the pattern of morphological variability, within constrained time comparisons, geographic displacement had a more significant impact. Furthermore, the validity of such comparisons depend on the impact other forces have on the rate of divergence across time and space. I end by considering how several other factors–demographic changes throughout the Pleistocene, climatic changes, and most importantly the application of cultural technology to ecological challenges–might impact evolutionary rates of divergence in Pleistocene humans.
Hopefully it is enjoyable and/or insightful.
