The first modern humans may have evolved on the south coast of South Africa, where they were making and using stone weapons far earlier than previously believed.
Scientists have found evidence for what they say is an advanced stone age technology dating way back to 71,000 years ago at Pinnacle Point near Mossel Bay.
A similar use of weapons doesn't seem to have taken hold in other regions of Africa and Eurasia until about 20,000 years ago.
"Every time we excavate a new site in coastal South Africa with advanced field techniques, we discover new and surprising results that push back in time the evidence for uniquely human behaviors," says Curtis Marean, of Arizona State University.
Thesea early people were carefully producing long, thin blades of stone that were then blunted or 'backed' on one edge so that they could be glued into slots carved in wood or bone. They could then be used as projectiles such as arrows, or more likely atlatls - tools used to throw spears, and much more efficient than the hand-cast version. The stone used to produce these blades was transformed for easier flaking by heat treatment.
This microlithic technology is known to have appeared briefly between 65,000 and 60,000 years ago during a worldwide glacial phase - but was thought to have then flickered out, perhaps as small populations struggled to survive.
But, says Marean, "Eleven thousand years of continuity is, in reality, an almost unimaginable time span for people to consistently make tools the same way. This is certainly not a flickering pattern."
Instead, says Marean, the appearance and disappearance of this technology is more likely a function of the small sample of well-excavated sites in Africa.
And it could have been a big factor in helping modern humans out-compete Neanderthals, who appear to have lacked true projectile weapons.
"When Africans left Africa and entered Neanderthal territory they had projectiles with greater killing reach, and these early moderns probably also had higher levels of pro-social (hyper-cooperative) behavior. These two traits were a knockout punch," says Marean.
"This probably laid the foundation for the expansion out of Africa of modern humans and the extinction of many prey, as well as our sister species such as Neanderthals."