By about 320,000 years ago, axe-wielding ancient humans had been thriving in the Olorgesailie Basin in modern-day Southern Kenya for nearly a million years. And, according to evidence from three new studies published together in Science, we now know this ancestral population became capable of advanced social and inventive behavior tens of thousands of years earlier than we previously thought.
The evidence for this was first collected in 2002, when researchers investigating the historically rich Olorgesailie area found a handful of sophisticated stone tools that were carefully shaped for specific tasks. These implements, some of which appeared to be suited for attachment to projectile weapons and others for processing fur and skins into clothing, were quite different from the larger multipurpose blades frequently unearthed in the basin since excavations began in 1942. Dated to between 1.2 million and 490,000 years ago, the primitive weapons, referred to as handaxes, are believed to have been used by hunter-gatherer Homo erectus groups.
In addition to the modified stone tools, the teams led by Rick Potts of the Human Origins Program and Alison Brooks of the Center for the Advanced Study of Human Paleobiology discovered both unshaped and modified obsidian fragments – a type of rock that does not occur naturally in Olorgesailie – and manganese and ochre rocks showing evidence that they had been processed to make dyes.
After enlisting isotopic dating expert Alan Deino from the Berkeley Geochronology Center, the collaborative group was able to reveal that the items were in use between 320,000 and 305,000 years ago. Taken altogether, the artifacts imply that the populations living during that time were creating specialized tools, decorating items with color, and trading items with other peoples. Yet before now, paleoanthropologists surmised that the shift toward such behaviors hadn’t occurred until the Middle Stone Age, approximately 280,000 years ago.
"We don't know what the coloring was used on, but coloring is often taken by archeologists as the root of complex symbolic communication," Potts said in a statement.
For context, the oldest fossil remains of a modern human, a Homo sapien, are also about 300,000 years old. While we can’t be certain if the Olorgesailie discoveries were used by a Homo sapien or a precursor species like Homo habilis, it appears that a rapid technological shift took place in the area between 490,000 and 320,000 years ago.
"This change to a very sophisticated set of behaviors that involved greater mental abilities and more complex social lives may have been the leading edge that distinguished our lineage from other early humans," said Potts in a statement.
To determine what environmental pressures may have precipitated our ancestor’s innovation, the team reviewed a wealth of geological, paleobotanical, paleofaunal, and geochemical data in order to reconstruct what living conditions in the basin were like.
The resulting snapshot in time is one of wet and dry climatic instability and frequent earthquakes. As with other periods in human history, Pott hypothesizes that the difficult periods drove selection of human ingenuity: The groups who quickly adopted better tools, social exchange networks, and early symbolic communication were the ones who survived.