In the cover story of the August Scientific American Curtis Marean of Arizona State University in Tempe tackles a long-standing question in paleoanthropology: How did our species, Homo sapiens, disperse so far and wide? Other human species colonized Africa, Europe and Asia but only our kind managed to spread across the entire globe. Marean suggests that the emergence in our species of a special propensity for cooperation and the invention of a game-changing technology—projectile weaponry—powered our ancestors’ march across the planet, allowing them to go places no member of the human family had gone before.

Marean’s hypothesis derives in part from discoveries he and his colleagues have made at archaeological sites on the South African coast where early H. sapiens once eked out a living. This summer the team returned to the region to dig at a seaside rock shelter at Pinnacle Point known as PP5-6, which they have been excavating since 2007. The site dates from about 90,000 to 50,000 years ago, preserving the shift from interglacial to glacial conditions at about 74,000 years ago.

Significant technological changes occur near that boundary. “Before 74,000 years ago people mostly use quartzite for stone tools, and they make large flakes, blades and points from it. After that transition they shift to heat-treated silcrete, and on that finer raw material they make little blades and microliths, probably for use as projectiles on advanced weapons,” Marean observes. “These are the oldest microliths in the world, and they must have been formidable weapons to use in hunting the large game that would have been moving across the plain in front of the cave that was revealed by lower sea levels of the glacial.”

The team also excavated some sites at a new locality known as Vleesbaai, a half-moon bay just west of Pinnacle Point. These sites are the open-air activity sites of the inhabitants of the Pinnacle Point caves and rock shelters. Whereas these ancient people based their camps in the caves and rock shelters at Pinnacle Point, they foraged for food and firewood, along with stone for making tools, at Vleesbaai. “This is a very unique preservation context where we have sites that sample both the homes and activity sites of people who would have belonged to the same social groups of hunter–gatherers,” Marean remarks.