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Tools tell a more complicated tale of the origin of the human genus

4:54pm, September 5, 2011
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The first animals that could arguably be called “human” made the evolutionary scene a little less than 2 million years ago.

These aren’t folks you’d mistake for modern-day Homo sapiens, or even the GEICO caveman. But they were clearly distinct from their more apelike predecessors. They had bigger brains, for one thing, and walked fully upright — presumably an adaptation to life out in the open rather than up in the trees. They hunted at least some of their food, tamed fire and may have spoken some form of language.

Paleoanthropologists have long been convinced that this revolutionary species, Homo erectus, was born on the African savanna almost 2 million years ago and spread over the next million years or so into Europe and Asia. Presumably its anatomical innovations and cultural sophistication made it the first species in the human evolutionary lineage that could survive outside Africa.

But some recent discoveries suggest that the story isn’t so neat and simple. Big events in the physical and cultural evolution of Homo erectus — the first campfire, the invention of the hand ax, the development of a capacity for long-distance travel — might just as easily have transpired on the steppes of central Asia as on the African savanna.

Much of the evidence for this heretical notion — it would have been outright laughable a decade ago — comes from a site called Dmanisi in the Republic of Georgia. Archaeologists started excavating a medieval village there in 1936, when native Georgian and Soviet premier Josef Stalin was just embarking on a genocidal purge that would kill more than a million people. Three-quarters of a century and one empire later, archaeologists are still digging at Dmanisi and finding evidence for earlier and earlier human habitation.

The oldest human bones from Dmanisi date back to 1.77 million years ago, almost as old as the earliest African fossils of Homo erectus. And though many paleoanthropologists would say the Dmanisi fossils are Homo erectus too, the bones actually look more primitive than that — primitive enough that some people give them a classification all their own: Homo georgicus.

Those bones alone are enough to suggest that some older, more apelike branch of the human family tree made it out of Africa long before the appearance of Homo erectus. But like an archaeological bottomless pit, Dmanisi has produced yet another layer of finds. Below the oldest bones are even older stone tools dating to 1.85 million years ago, the site’s excavators report in the June 28 Proceedings of the National Academy of Sciences. Like the fossils, these tools look too primitive to have been made by full-fledged Homo erectus.

Stone axes and other implements that Homo erectus used are known as Acheulean tools. In Africa, the oldest Acheulean tools date to 1.76 million years ago. More robust and versatile than earlier stone tools, they probably signal an increased role for meat in the prehuman diet. Acheulean tools are also considered an important factor in the migration of Homo erectus out of Africa sometime after 2 million years ago.

How could it be that very close to 2 million years ago, people who were physically more primitive than Homo erectus were using tools more primitive than the ones that supposedly came from Africa?

In the June Quaternary Science Reviews, Jordi Agustí of Universitat Rovira i Virgili in Tarragona, Spain, and David Lordkipanidze of the Georgian National Museum suggest that Homo erectus never expanded out of Africa at all. Shorter, smaller-brained members of the human lineage must have colonized Eurasia from Africa more than 2 million years ago, the researchers conclude.

That means that Homo erectus, with its big brain, fully human gait and sophisticated toolkit, could just as easily have migrated back into Africa as out of it. Bernard Wood of George Washington University in Washington, D.C., argues for that scenario in another paper in the June 28 Proceedings of the National Academy of Sciences. He even suggests that the controversial “hobbit” skull from the Indonesian island of Flores may be a descendant of whatever primitive member of the human lineage really was the first to leave Africa.

The only way to test a claim like that is to find more fossils. And now that it’s conceivable that pretty much all of the world’s largest landmass could have played a pivotal part in the rise of the human genus, there are plenty of places to look.

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