A stash of bone tools unearthed in South Africa hints that people have been acting like people far longer than commonly thought. The discovery may also challenge the popular view of what pushed our ancient ancestors to leave Africa.
It's widely believed that between 40,000 and 50,000 years ago, groups of modern humans, Homo sapiens, departed Africa, a theory known as the Out of Africa model. As Neanderthals and other hominids became extinct, Homo sapiens came to dominate the globe. To explain that singular success, scientists have focused on behaviors thought to be unique to humans, such as language and art. A popular theory is that before leaving Africa, Homo sapiens experienced a "creative explosion," acquiring sophisticated toolmaking abilities, linguistic skills, and other traits that helped them survive diverse environments. But still in dispute is how quickly people left Africa after developing these skills.
Bone tools unearthed during the last few years in South Africa's Blombos Cave, 300 kilometers from Cape Town, might help resolve that debate, says archaeologist Curtis Marean of Arizona State University, in Tempe. In the December issue of the Journal of Human Evolution, Marean's group describes its analysis of 28 of these finely crafted bone tools, likely used as awls for working hides to make clothes or bags, or as projectile points for weapons. Because the external coating needed to date the bones had worn off, the scientists used carbon dating and laser technology to measure the age of charcoal and marine shells in the sand layer where the tools were found. They estimated that the sand was deposited at least 70,000 years ago.
If the dates are confirmed, the tools would suggest that modern behaviors began to accumulate long before Homo sapiens migrated out of Africa, says Marean. He adds that the tools could also call into question whether the bigger brains that helped generate the "creative explosion" also spurred humans to leave Africa.
But others remain skeptical. Because large artifacts can slide through layers of sand, dating the sand alone can make them seem older than they really are, says Richard Klein, a paleoanthropologist at Stanford University in Palo Alto, California. A larger sample is needed, Klein says, and scientists have yet to find bone tools in any nearby caves.