[asa] AAAS Symposium on Human Origins

This afternoon I had the privilege of attending the Symposium on Human Origins at the AAAS meeting in Chicago. I wanted to record my notes while I still had some residual memory of them and thought some of you might enjoy reading them as well.

The Symposium was organized and sponsored by the Wenner-Gren Foundation for Anthropological Research. The moderator was Leslie Aiello of that foundation. Six speakers covered the spectrum of human evolution in the past 5 million years.

My overall impression was that the details of human origins are getting murkier. This is a good sign. It means a lot of new data is coming in. It reminds me of particle physics in the 60's when many new particles were being discovered but no one could make sense of it. In the 70's the standard model was developed that put it all in perspective. For human origins, all this new data seems confusing but will likely lead to better models. You'll see what I mean in the details that follow. It was also noted in several talks that the current trend is toward relating global climate change to hominid evolution. That is, paleoclimatology is increasingly viewed as a factor in influencing the direction of evolution and therefore can be used in helping to interpret fossils.

Bill Kimbel, Institute of Human Origins, Arizona State U. "Australopithecus and Human Evolution".
There were no known hominid fossils when Charles Darwin predicted that human ancestral fossils would be found in Africa. The prediction was based on his observation in various regions of the world that extant species were typically related to extinct species whose fossils were found in that region. The fossils of the genus Australopithecus are a clear and dramatic fulfillment of that prediction. Today there are 6-8 species in the genus. These do not fit in a simple lineage from the common ancestor with chimps to modern humans. The species range from A. Anemensis at 4.2 Mya to A. Afarensis to the co-existing species of A. Africanus, A. Garhi, and A. Aethiopicus at 1.4 Mya. The last one apparently split into A. Boisei and A. Robustus. They all seem to have gone extinct in a dead end except for A. Africanus which may have spawned the ancestor of H. Habilis. Virtually no fossils have been found in the range of 3.0 to 2.5 Mya.

David Lordkipanidze, Georgian National Museum, Tbilisi, Georgia, "Dmanisi and the Evolution and Dispersal of Homo"
In the last decade or so, Georgia has been the site of significant search for fossils. They have found significant lithic assemblage (tools!) similar to Olduwan tools from Africa. They have discovered 4 hominid skulls dated 1.8 to 1.7 Mya. Perhaps Dmanisi was the first stop for Homo Erectus in moving out of Africa. Yet there are some intriguing differences from H. Erectus and he is proposing a new species called H. Georgicus. Its relationship to H. Erectus is not clear.

Jose Maria Bermudez de Castro, National Research Center on Human Evolution, Burgos, Spain, "Atapuerca and Human Evolution in Europe"
About ten years ago, fossils were discovered in Atapuerca, Spain, that dated at 950 to 900 kya. Then in 2007 a 1.3 Mya fossil was found and reported in Nature in 2008. They have dubbed all of these H. Antecessor, again claiming distinctiveness from H. Erectus. Other speakers indicated they now were beginning to accept this designation.

Chris Stringer, Natural History Museum, London, UK, "Neanderthals and Human Evolution"
The split of the Neanderthal lineage and modern humans came around 370 kya. Nea appears to have been a very calorie intensive, meat-eating species. Their geographical range may have been farther than previously thought, possibly extending to Siberia and the mid-east. They have likely gone extinct. They may have been genetically absorbed into other Homo species, but according to yesterday's press release by the team in Germany, the comingling of DNA with H. Sapiens seems negligible.
There are four models of human migration: classic Out of Africa (OOA), OOA plus hybridization, Assimilation, and Multi-Regional Hypothesis. The last one seems to have been ruled out and the assimilation now seems less likely. Hybridization is apparently minimal, leaving the OOA as the most likely case.

Francesco d"Errico, National Scientific Research Centre, Talence, France, "Archaeological View of the Evolution of Humans and Modern Human Culture"
With symbolic thinking serving as a marker for modern human culture, the current models are all wrong. And all correct. Using pigmented beads and beadware as indicators it appears that neither an abrupt nor a gradual appearance of culture can explain the data, even though both have some merit. Rather, the record appears to be discontinuous with this behavior appearing, disappearing and reappearing at various times and places. There does seem to be a very significant difference between the lower and upper paleolithic periods with the latter showing a significant jump in bead usage.

William Jungers, Stony Brook U. Medical Center, NY "Homo Floresiensis and Human Evolution"
Jungers just returned from Indonesia a few days ago and is continuing research in this field. The story begins a decade or more ago when stone tools were discovered dating to 880 to 800 kya. This is the region beyond the Wallace line where supposedly no hominid could or had travelled. No fossils have been found that are associated with these tools. Then the so-called hobbit fossils were discovered. Including the fossils discovered this past year, there are now 5 or 6 individuals dating a mere 18 kya. The vigorous debate has now been essentially settled. No pathology or dwarfism leads to the characteristics seen in these fossils. (Glenn Morton said that on this list years ago!) The new species H. Floresiensis is accepted by almost everyone. As examples, the pectoral girdle, the iliac flaring, the wrist and the foot are all significantly more primitive than anything from modern humans. The foot can be characterized by a foot/femur length ratio of 0.72 (just like a bonobo) compared to a human ratio of 0.54. The big toe is very short and the other toes are long and curved. The result is that this species could walk but not run.
Though the controversy about its identity as a new species seems to be dying out, there is still a major controversy about what it is. Two main possibilities are being hotly contested:
1. an island-dwarfed descendent of SE Asian Homo Erectus
2. a descendent of an unidentified more primitive species ancestral to it and H. Erectus. (see A. D. Gordon, et. al., PNAS, Mar 25, 2008)

Possibility #1 would be puzzling because it would entail a peculiar unwinding of evolutionary "progress" from H. Erectus.
Possibility #2 would be puzzling because it would entail a third migration out of Africa, H. Sapiens, H. Erectus, and this ancestor.

So in summary, the big picture that Darwin predicted seems to be borne out. As long as there were only a few fossils, it was easy to draw a straight line connecting the species. Now that many more species have been found, it's harder to connect the dots. The years to come should be very interesting.

Randy

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Received on Fri Feb 13 22:26:56 2009