Â鶹ÒùÔº

Researchers propose new hypothesis for the origin of stone tools

Sharp stone technology chipped over three million years allowed early humans to exploit animal and plant food resources, which in turn played a large role in increasing human brain size and kick-starting a technological trajectory that continues to this day. But how did the production of stone tools—called "knapping"—start?

Three Cleveland Museum of Natural History researchers have proposed a new hypothesis for the origin of stone technology in human evolution. Associate Curator and the Robert J. and Linnet E. Fritz Endowed Chair of Human Origins Dr. Emma Finestone and Museum research associates Drs. Michelle R. Bebber and Metin I. Eren (both also professors at Kent State University) led a team of 24 scientists to the new hypothesis in the journal Archaeometry.

"I don't think it was a 'Eureka!' moment whereby hominins first made a sharp stone flake by intention or by accident and then went to look for something to cut," says Eren. "There is no reason to produce sharp stone tools unless the need to cut is already in place."

The new hypothesis proposes that for a substantial amount of time, before early humans made their own stone tools, they first used and relied on naturally sharp rocks produced via natural geological processes like rocks being knocked together in a stream bed or biological processes like animal trampling of rocks. However, previous research suggested that naturally sharp rocks that could have been used as cutting tools—called "naturaliths"—are rare in nature.

Not so, says the new research. Through fieldwork around the world and an extensive survey of scientific literature, Finestone, Bebber, Eren, and their colleagues show that sharp rocks are endlessly produced in a wide range of settings and thus may occur on the landscape in far greater numbers than archaeologists currently understand or acknowledge.

"In some cases, sharp rocks are produced by Mother Nature in the hundreds, thousands, or more," says Bebber, who observed one such locality during her fieldwork in Oman. "It is quite astonishing… natural knives were likely readily available to our hominin ancestors."

And Finestone's field research in Kenya shows that early hominin food processing sites often occur near naturally occurring sources of stone. "A hominin could have picked up and used a naturally sharp rock to process a carcass or plant material that might have been difficult to access using just their hands and teeth," says Finestone.

Only after using naturally sharp rocks to cut would there have been selective pressure for early humans to start knapping their own stone tools at will. For example, one potential motivation for knapping would be to solve the problem of limited supply and how to acquire sharp stone flakes in contexts where naturaliths were not present. Or perhaps knapping was a way to improve upon mother nature's invention by producing stone flakes with desired characteristics, rather than spend time and energy searching for naturaliths that possessed them.

"This is the most parsimonious hypothesis for the origin of hominin stone technology to date," says Eren. "But parsimony is not necessarily correct—archaeologists now need to test our hypothesis and search for naturalith use by hominins between 3 and 6 million years ago. It is an exciting prospect… if hominins are using naturally sharp rocks as knives, then the archaeological record is going to get a whole lot older."