August 11, 2004
Today, the excavators, transit fundis, and I completed our final lift of the season at Site 15. This last haul of about 100 fossil bones and stone tools helped a lot in figuring out exactly what happened at this site, about 990,000 years ago. We found several fragments of leg bones with sharp fractures, indicating that the bones had been broken while still fresh. They were found along side stone flakes, a couple cobbles, and teeth of a really old zebra. You can see two of the teeth, with worn chewing surfaces of an incisor (near the top) and a premolar (below), along with some small bone fragments. These finds are similar to something we observed some years ago - the teeth of zebras and antelopes discovered with concentrations of stone tools are almost always really worn down. In other words, they came from animals that either were very old or had eaten grass so amazingly abrasive that the teeth had neared the end of their usefulness very quickly.
What do you think this might mean? On the face of it, could it be that the Olorgesailie toolmakers were selectively butchering and eating old individuals, or at least animals that had teeth in pretty poor condition? Could it be, then, that the hominins were hunting these animals, focusing on weaker prey a little easier to bring down?
The issue of hunting and scavenging - that is, whether early humans killed large prey or had the ability to chase away lions and other carnivores from their kills - is a difficult one in our field of study. There are good reasons, and poor ones, that have been advanced on both sides of the debate. I think the debate is usually a "false" one - by that I mean that researchers begin by thinking of it as an "either/or" question (either the hominins hunted or they scavenged). Then they line up on one side or the other of the debate. In fact, if you look at most predators, including daunting ones like lions, there are times when they hunt for themselves and times when they scavenge from the kills of other predators. Hyenas are well known for scavenging, but they can also be fearsome killers and can be the main predator in any African habitat where lions are scarce.
The selection of old individuals is indeed a notorious hunting strategy - and so it seems at first glance that the Olorgesailie hominins were using this approach for obtaining meat. What I need to do, though, is to study all of the bones on which I can see butchery marks and percussion marks (the latter occur when the hominins smashed the bones to get to the fatty marrow inside). Are these the meatiest and most nutritious bones, like those from the upper leg (the femur and humerus)? Or are they the lower leg bones with little meat but pretty good sources of marrow?
At the excavation today, I was reminded of these questions - and, yep, there's a lot of studying to do back in the lab to answer them. But just as intriguing is the attention directed toward the cobble stones. Read the August 9th dispatch to see why. And look at the second photo, which shows a flat-topped rock we lifted from the Site 15 excavation today. Looks familiar? The indentation on the top indicates it was used as an anvil stone. Did early humans break the limb bones of a zebra and other animals on this rock, by using a hammerstone over and over again? Or, as we think at Site CL1-1, were there plant foods involved? The depth of the indentation suggests that there was a lot of food processing going on here, and the similarity to anvils used in preparing plant food is striking.
So, we would be wise to remember, the real challenge faced by early humans was getting food by hunting and scavenging AND by collecting edible plants.