With National Science Foundation support, Richard Klein and a multidisciplinary American/South African team will excavate for two seasons at the Ysterfontein 1 rockshelter, about 70 km north of Cape Town, South Africa. The excavation is designed to illuminate the behavioral changes that allowed modern humans to expand from Africa about 50,000 years ago and to swamp or replace the Neanderthals and other non-modern Eurasians.
Specialists disagree sharply about whether behavior changed abruptly in Africa just before 50,000 years ago or more gradually over a long interval between 250,000 and 50,000 years ago. The relevant African sites between 250,000 and 50,000 years ago are assigned to the Middle Stone Age (MSA), and the large majority lack standardized bone artifacts, art or jewelry, and other archaeological items that were widespread among historic hunter-gatherers and that became commonplace only after 50,000 years ago. Most MSA sites thus support the idea of abrupt change. However, there are a few, such as the Katanda cluster in the Democratic Republic of the Congo and Blombos Cave in South Africa, where markers of advanced behavior have been reported, and these sites support the gradual or piecemeal hypothesis.
Ysterfontein 1 contains artifacts and animal remains that can be used to test the alternatives, together with the idea based on a small number of other sites, that MSA people hunted and gathered less effectively than their successors. Ysterfontein 1 is particularly notable for large numbers of humanly collected intertidal shells, which can be used to track MSA population density, since average shell size probably reflects the number of human collectors. In aggregate, the Ysterfontein 1 shells tend to be very large, implying small MSA populations, but the new excavation aims to establish shellfish size layer by layer to determine if average size declines progressively through time. The project will use state-of-the-art technology to date the deposits precisely, but it is already clear that they span thousands or tens of thousands of years sometime between 100,000 and 50,000 years ago. Thus, a progressive decline in shellfish size would imply that MSA populations were growing through time, and it would support the piecemeal or gradual model of MSA behavioral change. It could even mean that population growth underlay the modern human expansion from Africa 50,000 years ago. In contrast, the failure of shellfish size to decline through time would imply consistently small MSA populations, and it would support the idea of abrupt behavioral change near the end of the MSA. The most plausible explanation for such abrupt change would be a serendipitous genetic mutation that promoted the modern human brain.
The project is intended primarily to inform on the behavioral origins of modern humans, but it will also serve to train American and South African students in state-of-the-art methods for recovering large, unbiased, stratigraphically controlled artifact and faunal samples from a deeply stratified rockshelter. The need for future generations of archaeologists to expand the sample of carefully excavated sites is vital not only for resolving uncertainties in modern human origins, but also for illuminating many other outstanding problems in human evolution.
