Until recently most anthropologists believed that "modern" human behavior requiring symbolic thought did not originate until 40,000 or 50,000 years agoaround the same time that early humans first migrated out of Africa.
(See an interactive map of human migration.)
The archaeological record, particularly in Europe, suggests an explosive proliferation of such behavior about 45,000 years ago.
But a 2001 discovery by archaeologist Christopher Henshilwood shifted the debate on such theories.
Henshilwood's team found specialized bone tools and engraved red ocher in South Africa's Blombos Cave and dated them to 70,000 years ago, suggesting that the humans who left Africa might have already exhibited "modern" behaviors.
(Read "African Bone Tools Dispute Key Idea About Human Evolution" [November 8, 2001].)
Rupert Isaacson is an Austin, Texas-based journalist and the author of The Healing Land: The Bushmen and the Kalahari Desert. He says that rituals like those Coulson describes are depicted in ancient paintings throughout the Tsodilo Hills and endure among today's San, also known as Bushmen.
"That tradition remains unbroken," said Isaacson, who also advocates for the San through the Indigenous Land Rights Fund.
"Anywhere you go where Bushmen still exist you'll find trained healers who know how to go into trances, and they do them for the community at sacred sites, where they are more powerful."
Michigan State University anthropologist Larry Robbins studied Rhino Cave in the mid-1990s and has previously suggested that the site might have been used for rituals, based on rock paintings found there.
But he's not certain that such rituals were being practiced as far back as 70,000 years ago or that the "python rock" played a role.
"I'm not convinced that the rock is an intentional snake at all, or that all those depressions and grooves belong together in terms of their age," he said.
"It could be that perhaps even quite recently someone decided to make it look a little bit more like a snake."
"I'm also not convinced that the evidence shows a 70,000-year-old ritual," he added, "but I'd be very happy if that turns out to be the case."
Stanley Ambrose, an anthropologist at the University of Illinois at Urbana-Champaign, has similar reservations about the findings of Coulson's team.
He notes that dating artifacts in such a locale is a very difficult task, with different techniques producing widely divergent results.
"In this case I don't see anything that can unambiguously date these [artifacts]not in that time period and that place," he said.
Alec Campbell, founder of Botswanas National Museum and an authority on the Tsodilo Hills, suggested that some of the grooves on the python rock may have been made around the time that Coulson's team suggests. But he believes that other grooves were made perhaps as recently as a thousand years ago.
"You get these [grooves] all over the world, and they go back a very long time, possibly 300,000 years in one Indian location," he said.
Campbell is also unconvinced that the rock is meant to resemble a snake.
"The [grooves] likely possess some sort of symbolic purpose and possibly a religious one," he said.
"But to say that this particular frieze of [grooves] represents a snake and it's the earliest religious site that's known, I just don't think that makes sense."
The cumulative evidence, however, is convincing to Coulson.
"It is the whole package of behavior traits from our excavations that has led us to conclude that the only plausible explanation is that this site was used for ritual purposes," she said.
"The intentional stuffing of quartz flakes into a crack in the wall beneath the snake, the exceptional treatment of all the points recovered, [these] are behavioral patterns that do not fit any patterns we know of from the many other sites [from this era]."
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