Human ancestor development may have occurred earlier than thought

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Archaeologists in Africa have discovered evidence suggesting that human ancestors demonstrated sophisticated behavior 80,000 years earlier than previously thought, according to research published Nov. 13.

The paper found that 280,000-year-old pointed rock fragments were used on the tips of throwing spears by Homo heidelbergensis — a species that was most likely a predecessor of Neanderthals and Homo sapiens. The study, published in scientific journal PLOS ONE, was conducted by an international team of researchers, including head author Yonatan Sahle, a postdoctoral researcher at UC Berkeley’s Human Evolution Research Center.

The fashioning of stone-tipped spears as a composite weapon used for throwing rather than thrusting is indicative of complex behavior that researchers previously thought distinguished Homo sapiens from their less capable ancestors, according to the study.

“Projectile weapons are among the technological traits considered as the indications of ‘complex’ behavior,” Sahle said. “Our findings for the earliest composite projectile show that hafted and thrown spears predate the emergence of our species by about 85,000 years.”

Years of excavation at an Ethiopian Stone Age site known as the Gademotta Formation allowed archaeologists to collect scores of pointed shards of volcanic glass known as obsidian, 16 of which indicated features unique to impact at high velocity. Archeologists were recently able to study the artifacts’ shapes, breakage patterns and signs of hafting — a technique of attaching a handle to a blade — in order to determine whether the pointed stone was used as a tool or a tip on a projectile hunting weapon.

To rule out the possibility that hafted and broken pointed pieces of obsidian were used for handheld thrusting tools such as daggers, researchers used close analysis of the distinct microscopic features on the artifacts to determine whether the force of impact on the tool is specifically associated with projectile weapons such as javelins.

“(The) method allows one to confidently identify the mode of delivery of a weapon based on the unique crack velocity associated with different impact sources,” Sahle said. If the velocity of the impact crack fulfills a certain threshold, then it can be attributed to projectile use and no other known impact source, Sahle explained.

In a study published last year, a separate group of archeologists linked the earliest hafted spears used for thrusting into prey with Homo heidelbergensis — aka the Heidelberg Man. Now, the discoveries at the Gademotta site provide evidence that complex technological behaviors were not only the domains of Homo sapiens but also part of the era of the Heidelberg Man.

“(The artifacts) also derive from a region often considered as the backwater of technological innovations,” Sahle said. “Therefore, they remind us of the need to rethink our views that ‘complex’ behaviors emerged much later only among Homo sapiens and in southern Africa.”

Exhaustive study of the paleolithic record of southern Africa has made the region an integral part of the examination of the emergence of modern humans. The data in the recent study now include eastern Africa as a possible source of humans’ historical development as well, according to Sahle.

Contact Jeff Landa at [email protected] and follow him on Twitter @JeffLanda.