July 29, 2004

John and Alison left this afternoon to meet their children, who happen to be visiting Nairobi. They'll all go on a safari together to see the famed animals and landscapes of Kenya. While they're gone for a few days, work is continuing in Locality G. The excavators have uncovered many more stone tools that belong to the Middle Stone Age (MSA), and survey by John and Alison has uncovered evidence of Sangoan tools lying on the surface of the eroded slopes. As I mentioned before, the MSA is characterized by small, specially-shaped flakes, while the Sangoan (the technology between the Acheulean and MSA) is characterized by three-sided picks and large, crude flakes. You can see large Sangoan tools at the top of the photograph, and small, fine MSA points at the bottom.

Tools from Locality G

What's particularly interesting about the Sangoan and the MSA is that these technologies are thought to be roughly the same age as the origin of our own species, Homo sapiens. We know that the humans who lived after 200,000 to 150,000 years ago were the same biologically as we are (we call them biologically modern humans). But one of the big questions remaining in paleoanthropology is, when did they start acting the same as we do?

This may seem an odd question, but the first step is to define what we mean when we say "acting the same as we do". That is, what types of behavior make a modern human unique? Most archeologists include things like the ability to speak, to produce art and to think in a symbolic manner. They'll also include the ability to make complex tools and to engage in complex social behavior, like trading between groups, in their definition of modern behavior.

The problem is it's very hard to 'see' these behaviors in the archeological record, because things like words or complex grammar don't leave any fossils behind. So, archeologists have come up with several different lines of evidence of what they think defines modern behavior. I've made a table where you can see what I'm talking about. On the left side is the name of a particular behavior, and on the right is the kind of evidence archeologists use to detect that behavior.

Behavior: Artifacts:
Personal decoration Beads, jewelry, red ochre (a kind of earth that can be used to make red pigment)
Fishing Harpoon points
Art and symbolic behavior Drawings on cave walls, carving on bones
Complex tools Evidence of hafting (using handles to hold the stone blades)
Trading (exchange between distant groups) Significant amounts of stone material over 100 km away from its source
Ritual Burials with grave goods

This list doesn't exhaust all the possible ways of defining "modern behavior", but it gives you some idea of what archeologists look for. But when do we see these different behaviors first crop up in the archeological record? There are two basic camps in the debate. The first is what I call the "late, abrupt hypothesis", which means that the capacity for modern human behavior didn't evolve until very late, about 50,000 to 40,000 years ago. The second camp, called the "early, gradual hypothesis", claims that the capacity for modern behavior developed beginning a couple hundred thousand years ago, and that we see archeological evidence of modern behavior over many tens of thousands of years. Advocates of the late, abrupt idea consider the arrival of modern humans in Europe and the explosion of cave art, jewelry, carvings, complex tools, and other inventions on that continent between 40,000 and 30,000 years ago to mark the big event - the dawn of modern human cultural behavior. But advocates of the early, gradual interpretation point to evidence in Africa of pigment grindstones, complex tools, and specialized types of foraging, such as fishing, which are all earlier than 50,000 years old. According to this idea, then, it wasn't one single genetic change that spurred the development of modern human behavior. Instead, the capacity was built up slowly, and modern behavior became more and more advanced over time. It turns out that one member of our research group, Alison Brooks, is a strong supporter of this second hypothesis. She's done a lot of research to show that there's evidence of beads and other symbolic behavior, like cave art, in Africa between 90,000 and 70,000 years old. Part of her interest in working with our team at Olorgesailie is to see whether there's more evidence one way or the other about the evolution of modern behavior.