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For all the attributes that humans share with other animals, there is a trait that clearly sets us apart: our reliance on symbolism. Exactly where and when in our lineage this and other aspects of modern human behavior emerged, however, have proved difficult to pinpoint. The fossil record indicates that anatomically modern humans had evolved by 100,000 years ago. Yet clear and abundant evidence for behavioral modernity only appears after 40,000 years ago. Now new findings may help to close that gap. According to a report published online today by the journal Science, excavations at a South African cave site have turned up two pieces of ochre bearing symbolic engravings that date back about 77,000 years to the so-called Middle Stone Age (MSA).

Ochre, a form of iron ore, appears relatively frequently among the scraps of culture left behind by our Stone Age predecessors, who may have used it to tan hides or to paint with. But the newly discovered pieces bear unequivocal signs of use as symbolic objects. Christopher S. Henshilwood of the Iziko Museums of Cape Town and his colleagues report that both specimens bear cross-hatched markings that appear to have been produced through a deliberate sequence of choices.

"The Blombos Cave motifs suggest arbitrary conventions unrelated to reality-based cognition ... and they may have been constructed with symbolic intent, the meaning of which is now unknown" the authors. note. "These finds demonstrate that ochre use in the MSA was not exclusively utilitarian and arguably, the transmission and sharing of the meaning of the engravings relied on fully syntactical language." Given that evidence of abstract thought is the only criterion scholars seem to agree on when it comes to identifying modern behavior in the archaeological record, the team writes, "it seems that, at least in southern Africa, Homo sapiens was behaviorally modern about 77,000 years ago."

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