August 6, 2004

The National Museums of Kenya is one of the finest museums (actually a combination of many different museums) in all of Africa. They do a good job of trying to preserve many outdoor museums, including the one at Olorgesailie. During our excavation season here, I often talk to school groups, tourists, and local visitors, all of whom are eager to see the famed concentrations of handaxes that are on display. A couple weeks ago, I talked to the geology students and a group of visitors from a United Nations school in Nairobi, who were tagging along, about one of the most interesting handaxe sites. It's called DE 89, and its original excavation was carried out by Louis Leakey (in the 1940s) and later by Glynn Isaac (in the 1960s). The site is about 900,000 years old.

Handaxes at DE89

In the photo above, you can see part of the excavated concentration of stone tools, which was left in place for visitors to see. Why are all of these handaxes, more than 500 of them, clustered together here? OK, let me give you some clues to see if you can figure it out.

Clue #1: The artifacts are found in sands deposited in a stream channel. It could be that the artifacts were moved to this spot by fast-moving water. It would have to be a strong current of water, since the handaxes are large and heavy, and it would take a lot of force to move them.

Clue #2: The channel was very broad but very shallow, probably a maximum depth of no more than about 50 centimeters. The channel would have been dry during the dry season. Hmm, this means that the water flow was not very strong.

Clue #3: The handaxes generally have pretty fresh, sharp edges, and the flaking scars made by the toolmakers are clear. However, there aren't a lot of really small flakes - the debris that came from chipping them at the spot is gone. OK, this evidence further suggests that the handaxes weren't very affected by water flow, which otherwise would have abraded the edges and flake scars. But either the hominins didn't actually make the stone tools at DE 89, or the flow of water in the sandy channel was strong enough to move the small stone chips away.

Clue #4: There were lots of bones of a large species of baboon, known as Theropithecus oswaldi, found in the excavation, and these bones were found close to the handaxes. In fact, a minimum of about 90 individual baboons died at this site. Gee, doesn't it seem obvious? The hominins must have been hunting, butchering, and eating the baboons.

Clue #5: The baboon bones don't show any definite stone-tool butchery marks (or percussion marks from opening the bones for the fat-rich marrow). But carnivore bite marks can be seen. This means that we don't have clear evidence that the toolmakers were actually eating the baboons, but carnivores did gnaw on their bones.

So, what does all this add up to? What do you think?

DE 89 remains a mystery to archeologists. It's possible that early humans obtained meat from the baboons from very careful butchery. Or maybe the bone surfaces just aren't well enough preserved to show tool cut marks. But it's odd, then, that the surfaces do show the tooth marks left by carnivores. We know that baboons are often the prey of predators at night, where the baboons sleep in trees or cliffs near water holes.

You may recall that one reason we think that early human fossils are so rare at Olorgesailie is that the hominins were living in the highlands. Almost certainly they weren't living (and dying) down by the water's edge at night, when predators are very active. As you may also recall, we think that the dense handaxe concentrations may have been left by the hominins at watering holes before they walked back up into the highlands, following a trip to the lowlands to obtain meat and plant foods. Finally, remember (part of clue #2) that the shallow stream channels were probably dry at times, and we think they may have contained a few ponds as the water dried up.

If so, it's possible that the handaxe-makers left their handaxes near these water holes during the day before they traveled along one of the nearby volcanic ridges back up to Mt. Olorgesailie. At night time, the baboons may have slept near these same dry-season water holes, where predatory cats and hyenas may have lurked - and where they did their harm to unsuspecting baboons.

It's interesting, then, that the baboon bones and the handaxes maybe didn't have much to do with one another, even though they are found together. It's still a mystery, and different researchers have different interpretations of this intriguing site.