BY BRONWYN BARNETT
By 100,000 years ago, Homo sapiens had evolved on the continent of Africa. For 50,000 years, they were confined there, and they behaved just like H. neanderthalensis then inhabiting parts of Europe and H. erectus living in Asia. Then their behavior changed dramatically -- and anthropologists aren't entirely certain what happened.
Today, breakthroughs in genetics may provide anthropologists with valuable insight into what happened all those years ago and why.
Richard Klein, a professor of anthropological sciences at Stanford, has an explanation, albeit a controversial one: "I think there was a biological change -- a genetic mutation of some kind that promoted the fully modern ability to create and innovate." Klein will present his perspective Feb. 15 at the annual meeting of the American Association for the Advancement of Science in Denver.
His comments are part of the symposium "Revolution and Evolution in Modern Human Origins: When, Where and Why?" which also will include talks by Alison S. Brooks (George Washington University and the Smithsonian Institution), Terrence Deacon (University of California-Berkeley), Francesco D'Errico, (Institut de Préhistoire, Université de Bordeaux), Richard Potts (Smithsonian Institution), Mary Stiner (University of Arizona) and Wentzel van Huyssteen (Princeton Theological Seminary).
For the past 35 years, Klein has traveled to South Africa at least once a year to study the change that spurred human creativity. "When you look at the archaeological record before 50,000 years ago, it's remarkably homogeneous," he says. "There are no geographically delineated groups of artifacts." Artifacts made by modern humans of that era in Africa closely resemble those found in France, made by Neanderthals.
Then something happened.
"Suddenly, modern-looking people began to behave in a modern way, in producing art and jewelry and doing a whole variety of other things that they hadn't done before," he said.
Over the next 10,000 years, these behaviorally modern humans arrived in Western Asia, Eastern Europe and finally Western Europe, and displaced the Neanderthals as they went.
"Suddenly you see geographically and chronologically restricted groups of artifacts with a lot of style involved in the manufacturing, and the geographic distribution is very limited," he said. Anthropologists believe these differentiated remains indicate the presence of different ethnic groups.
Why did people suddenly begin to behave in a more modern fashion? This question has been a source of discord among many anthropologists. Some think people's behavior changed gradually. Klein thinks they're wrong.
Klein holds a minority opinion among anthropologists, most of whom believe the change to modern behavior was the result of "some kind of cultural or demographic change," he said. Many of his opponents believe a population buildup could have caused the change, but Klein sees no evidence for this theory.
But new breakthroughs in the field of genetics may lend Klein's view convincing support. Genes interact with environment to influence appearance, behavior and mental faculties. By isolating a gene and finding out when it evolved, scientists can obtain clues that help them figure out when humans developed certain skills, and possibly what triggered a change in behavior.
Every generation of humans produces new mutations, or variants, among genes. The longer a gene has existed, the more variants of that gene tend be found in today's population. By isolating a gene and measuring the amount of current variation, and estimating the rate at which the mutations have occurred, geneticists can give anthropologists rough estimates of when that particular gene evolved.
Geneticists have done this with the foxp2 gene, which is involved in human speech and language. The dating indicates that this gene evolved "sometime between last Tuesday and 200,000 years ago," Klein said. He believes this estimate is extremely conservative, and that the gene evolved closer to 50,000 years ago -- a date that would support a biological cause for the change in behavior that anthropologists observe.
"There may be other genes that we can identify that all changed in some way around 50,000 years ago. They would have to be genes involved in cognition or communication. If you can show that, then my idea would be, I think, widely accepted."
What about fossils? Do they reveal evidence of a biological change? "Not really," Klein says. "There's nothing about the outside of the skull, or even the inside, that tells you very much about how a brain functioned." He hopes the genes will prove to be a valuable supplement to a fragmented fossil record.
In recent years, scientists have developed increasingly efficient ways to isolate and accurately date genes. Technological advances have allowed them to analyze vast amounts of genetic data in ever-shorter periods of time. "I'm very excited about this gene work," said Klein. "The technology is just amazing." But the sea of available genetic data is huge. "There's an enormous amount of work to be done on this," he says.
He admits that anthropologists may never be completely sure what happened 50,000 years ago. "It's kind of like the criminal justice system," he says. "It's never 100 percent. ... There are always some ambiguities, some contradiction in the evidence, even when eyewitness accounts are available. And the fact is, of course, that the jury themselves cannot be eyewitnesses," he says. "Unless we get a time machine or eyewitnesses, there will always be some uncertainty about what happened in prehistory."
Bronwyn Barnett is a
science writing intern with Stanford News Service.
Stanford Report, February 26, 2003