Their model begins about 250,000 years ago, when Homo heidelbergensis arrived in India toting crude stone tools. Digs in central India in the 1980s turned up skeletal remains of the species, and other sites revealed almond-shaped hand axes chipped from stone.
Meanwhile in Africa modern humans arose about 190,000 years ago, most archaeologists believe. These humans too developed stone tools.
Scattered evidence, such as red ochreperhaps used as body paintsuggests early African humans also dabbled in the creative arts.
The new theory posits that as much as 70,000 years ago, a group of these modern humans migrated east, arriving in India with technology comparable to that developed by Homo heidelbergensis.
"The tools were not so different," Petraglia says. "The technology that the moderns had wasn't of a great advantage over what [Homo heidelbergensis] were using."
But modern humans outcompeted the natives, slowly but inexorably driving them to extinction, Petraglia says. "It's just like the story in Western Europe, where [modern humans] drove Neandertals to extinction," he says.
The modern humans who colonized India may also have been responsible for the disappearance of the so-called Hobbits, whose fossilized bones were discovered recently on the Indonesian island of Flores.
But Athreya of Texas A&M argues that the evidence for such a "replacement event" in India remains weak.
"You have to explain the reasons for the replacement, [such as] technical superiority," she said.
"The genetic evidence shows there were multiple migrations out of Africa, so there would have been multiple migrations into [India]. But I think these migrating populations didn't completely replace the indigenous group."
Petraglia and James's report presents evidence of creativity and culture in India starting about 45,000 years ago. Sophisticated stone blades arrive first, along with rudimentary stone architecture.
Beads, red ochre paint, ostrich shell jewelry, and perhaps even shrines to long-lost godsthe hallmarks of an early symbolic cultureappear by 28,500 years ago.
This slow change is in contrast to what many scientists believe played out in Europe. Modern humans blew through the continent like a storm about 40,000 years ago, and Neandertals quickly disappeared.
The switch happened so rapidlyas evidenced by the sudden arrival of advanced stone tools and an explosion of cave painting and other artthat anthropologists call it the "human revolution."
"What we have is a much patchier, very slow and gradual accumulation of what we call modern human behavior in South Asia," Petraglia says.
"And that just simply means that culture developed in a slightly different way in South Asia than it did in Western Europe."
A dearth of fossils and artifacts in India makes Petraglia and James's research even more valuable, writes Robin Dennell, professor of archeology at the University of Sheffield, in a comment accompanying the study.
The subcontinent has produced just one set of early Homo sapiens fossils, found in a cave in Sri Lanka and dated to about 36,000 years ago.
Despite this, Petraglia hopes his analysis throws new light onto early human history in India.
"We're trying to give a wake up call to anthropologists saying that we have to be looking at all parts of the world," he says.
"If we really want to tell the story of human evolution we've got to bring all parts of the world into the story."
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