August 3, 2004

Last week I mentioned the debate about modern human origins - how some people think that modern human behavior originated quite late in prehistory, around the time when biologically modern humans arrived in Europe, while others think it developed earlier and very gradually, particularly in Africa.

Alison is a strong proponent of the early, gradual hypothesis. Her work in other places in Africa has shown many cases where early modern humans had more complex behavior than was expected during the Middle Stone Age (MSA). In Botswana, fossil animal bones showed that humans were hunting large, dangerous animals that no one thought they'd have the technology or ability to go after. At Katanda in Zaire (now Democratic Republic of Congo), Alison and John found barbed bone points and many catfish bones, all from fish of the same size, which is good evidence of fishing. In Ethiopia, there were many stone tools made from obsidian, which was not found locally, and this suggests long distance trade.

Research on the MSA at Olorgesailie may bring more evidence to this debate. So far, we've found a few artifacts that may indicate an early emergence of modern behavior. I've already mentioned the stone points that Alison and John have found in previous years. These points are often made of obsidian or chert, neither of which is found in the Olorgesailie basin. It could be that some sort of social system was in place that allowed these humans to exchange (trade) them or otherwise get these stones without having to travel great distances to get them. While we don't often see complete points, the ones we do have seem to have been specially thinned and shaped, the way you'd expect if the maker had wanted to haft the points. We find many more broken point tips, which we'd expect if they had been hafted onto a shaft and then hit against something hard. Besides the points, another clue of modern behavior at Olorgesailie is the fragment of a grindstone, shown in the photograph, which seems to have traces of red ochere on it. As I mentioned before, red ochre is a kind of earth used in making red pigment, and the grinding of ochre may signal some sort of symbolic or artistic behavior. This stone was found in sediments that date to about ninety thousand years ago - rather older than most researchers who are in the late, abrupt group would expect.

Grindstone fragment