Stone Age era hand axes, long thought to be simple tools early humans created without needing higher-order brain functions, are in fact the result of complex cognition, a new study suggests.
Stone tools created by striking a large stone with a piece of bone, antler, or another stone to shape or sharpen it represent some of the best evidence of human behavioral change over time, researchers say.
While simple stone flakes used as tools date back 2.6 million years, the skills involved in making a more sophisticated Stone Age hand ax are "more complicated and nuanced than many people realize," says study leader Dietrick Stout, an archaeologist at Emory University. "It's not just a bunch of ape-men banging rocks together. We should have respect for Stone Age tool makers."
Researchers at Emory, along with colleagues at Britain's Exeter University and France's Aix-Marseille University, wanted to see if they could determine what amount of brain power was needed to recreate a hand ax of the Late Acheulean period 500,000 years ago.
Such an ax is much more complex that a simple flake tool, having a carefully shaped stone core that tapers down to sharp, symmetrical edges.
"We wanted to tease apart and compare what parts of the brain were most actively involved in these stone tool technologies, particularly the role of motor control versus strategic thinking," Stout says.
Six Exeter archaeology students were trained in a skill known as "knapping" to make stone tools, both simple flake tools and the more complex hand axes.
MRI scans were performed while the students made decisions about how and where to strike a stone to get the desired result.
The researchers detected what's known as executive control function, linked with prefrontal cortex activity, which lets a person predict what's liable to occur as a future consequence of an action.
"It's kind of like mental time travel, or using a computer simulation," Stout explains. "It's considered a high-level, human cognitive capacity."
It suggests early humans, in fashioning hand axes, were not engaging in rote, autopilot brain activity but were performing some sophisticated thinking, he says.
And the majority of the axes created by the student participants wouldn't have passed muster compared with an actual Stone Age ax, he notes.
"They weren't up to the high standards of 500,000 years ago," he says.
The researchers had previously determined that creating stone tools created structural alterations in pathways connecting the brain's frontal and parietal lobes, changes linked with improved performance. The results were published in the journal PLOS One.
"This adds to evidence of the importance of these brain systems for stone tool making, and also shows how tool making may have shaped the brain evolutionarily," Stout says.
