This Week in the Primate Family: What Are Brains Good For?



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Aug. 12 2010 12:38 PM


In its current cover story, Nature publishes research from archaeologists who have concluded that proto-humans were cutting meat off bones at least 3.24 million years ago—meaning stone tools may have been in use 800,000 years earlier than previously thought.

The evidence is limited: two fossil bones, each with marks on them that look like the tracks of stone tools. But paleoanthropologists spend a lot of time figuring out how to tell intentionally sharpened rocks from regular rocks, and finding ways to distinguish the cut marks those tools make on bones from the marks made when bones are gnawed on or stepped on:


Some of the cuts are V-shaped in cross section, for instance — a shape characteristic of those made by sharp tools — with scratches inside the cuts left by the tool's rough edge. Other marks showed signs of scraping, and still others indicated that the bones had been bashed with blunt rocks — perhaps in an effort to reach the marrow.

Paul Renne directs the Berkeley Geochronology Center in California, and has worked on studies of some of the oldest known cut-marked bones found previously. "It sure looks convincing to me," he says of the new find.

This is a routine kind of surprise in paleoanthropology; the longer people look, the further back the human or prehuman story goes. What makes this find noteworthy is that if the scientists are right, the documented use of cutting tools has jumped clear back out of the genus Homo , into the australopithecines.

The area where the bones came from is associated with Australopithecus afarensis , the small-brained, upright-walking species best known by the fossil skeleton nicknamed " Lucy ." People usually call Lucy a human ancestor, because it's easy shorthand and it makes better copy, but when you get back into 3 and 4 million years ago, it's hard to draw a straight line of descent. There were multiple kinds of upright-walking apes around, and it's possible that Australopithecus afarensis was a side branch on our family tree. Our direct forebears might have been some other bipedal primate instead.

But that only emphasizes what's really striking about the find: these bones were cut up by creatures that were very far from being human beings. Our human brain, that big wrinkly mass of fat and nerves we're so proud of, was nowhere near the scene.

Yet the australopithecines, with their unimpressive skulls, were butchering carcasses, using rocks that the scientists say had to have come from more than three miles away. They may have been scavenging rather than hunting; they may have found naturally sharp rocks rather than actually making them. Even so, they were stepping into what we think of as human territory:

It's an important find, says David Braun, a Palaeolithic archaeologist at the University of Cape Town in South Africa, because our closest living relatives don't engage in such behaviours. "Chimpanzees do not recognize large animals or carcasses killed by other animals as food," he says. "At some point, hominins did."

Besides being the umpteenth nail in the coffin of vegetarian propaganda, the discovery helps deepen the mystery of what makes humans special. That brain of ours—we're sure that it marks a distinct break from other animals, that its higher functions evolved for some task unique to us.

The more we learn, though, the less clear it is what that cognitive application would have been. Such definitively human behaviors as using words and banding together to kill for territory have already turned up outside our species. Now we have large-animal butchering being done by animals that were basically chimpanzees with better posture.  

On the other hand, this week also brings news that we may have been overestimating some of our primate relatives. The Boston Globe reported on Tuesday that Marc Hauser, the Harvard professor who has gotten famous studying the relationship between primate and human cognition, is on leave after being accused of academic misconduct :

The findings have resulted in the retraction of an influential study that he led. "MH accepts responsibility for the error,’’ says the retraction of the study on whether monkeys learn rules, which was published in 2002 in the journal Cognition.

Back in 1995, the Globe reports, another Hauser study was challenged, with another scientist reviewing Hauser's research videotapes of cotton-top tamarins and concluding "there was not a thread of compelling evidence" that the monkeys could identify themselves in a mirror, as claimed.

The easy punchline would be to say that only human beings would think to fake results like that. Unfortunately, chimpanzees are good at deception , too.