RETURN TO THE HOMINID JOURNEY....
So is multiregionalism dead? Should Java Man and the Neanderthals be barred from any future family reunions? Not at all -- at least not if you ask Alan Templeton, a geneticist at Washington University in St. Louis, Missouri. His quarrel with Eve goes back to 1991, when he showed that Wilson's team had inadvertently misused the computer program that constructed their evolutionary tree. That part of their work, he proved, was invalid.
Now Templeton is launching a more sweeping critique, to be published in an upcoming book. He argues that the genetic studies to date have made a fatal, untested assumption: They presume that different populations of humans could not, or would not, interbreed.
For instance, the Out of Africa supporters assume that modern humans left Africa some 100,000 years ago and scattered across the planet. The fragmented populations were never again in close enough contact to interbreed. If this is what really happened, any genetic mutation they all shared and passed to current populations must have cropped up before their populations split.
Under these assumptions, the 200,000 year date for Eve has important implications. It tells us when our species arose and helps pinpoint the date of our great migration out of Africa. But what if, as Wolpoff and Templeton believe, there was no one great migration, no time when the population fragmented into isolated units? What if, instead, different human groups have always been moving about and swapping genes through breeding? If that is true, a 200,000-year-old date for Eve has no special meaning. It doesn't represent the first budding of a new branch on the family tree. Nor does it suggest that a conquering horde of Eve's descendants wiped out more ancient lineages. It just means that people were simply breeding at random, and Eve's mutation just happened to arise by chance and spread by interbreeding through the species.
Templeton gives a modern-day analogy: the presence of a gene for sickle cell anemia in Caucasians in Portugal. The gene traces back to a mutation that occurred in Africa and spread through interbreeding between Africans and Europeans. "The Africans didn't come up, reconquer the Iberian peninsula, kill off all the Europeans, and that's why there are sickle cell alleles in Portugal today," he says. The presence of the sickle cell gene in Portugal "means that Portuguese and Africans have met and they've interbred, just like humans tend to do."
Templeton interprets the genetic data used to support the Out of Africa theory in the same way. To him, the evidence suggests unbroken interbreeding, not a complicated scenario that requires people to migrate en masse out of Africa, to fragment and then to annihiliate other established groups. "There wasn't an Out of Africa event," he says. "It wasn't even a close call."
Of course, Out of Africa proponents haven't let Templeton go unchallenged. Many other geneticists, such as Masatoshi Nei of Pennsylvania State University, think it's highly implausible that all of the human groups were in close enough contact to stay genetically connected. It's far more likely, Nei says, that populations were scattered and isolated for long periods. The world of Homo erectus, after all, was a mosaic of different environments. Once a population settled down, its members would stop breeding with groups in other areas. Over time, so many genetic differences would build up that the population would become reproductively cut off as well. Unable to breed with other populations, it would become a separate species.
Nei concedes that Out of Africa does rest on untested assumptions. But he says multiregionalists make unsupported claims as well. For instance, Wolpoff and others argue that populations today retain distinct regional features dating back a long time, like the phenomenal Neanderthal nose. This suggests that mixing of genes and dilution of traits between populations was limited. But to explain how we evolved as a single, unified species, they also claim that people must have interbred widely across continents. How can the multiregionalists have it both ways? Nei asks.
No one knows what will resolve this dispute. More evidence would help: fossils with more reliable dates, genetic tests with more discriminating power. But even so, the conflict may remain intractable for reasons that have nothing to do with science. The issue, after all, involves our own species, our own history. And as Tattersall and Templeton point out, when we study ourselves we can never shake off deep-seated bias and emotion.
In Tattersall's mind, scientists show this bias by lumping diverse human forms together -- the multiregionalists' penchant for linking everything from Homo erectus to Homo sapiens into "one big happy species," as he puts it. Paleontologists don't give other animals such special treatment, he says. Nor do they blink at the notion of one species driving another to extinction. Why is it unthinkable that our ancestors did the same?
Templeton says Out of Africa proponents betray bias by excessively splitting the human line. We make far too much of our anatomical differences, as our fixation on trivial racial differences so often tragically demonstrates. Biologists who study, say, fruit flies know that each population can look quite distinct, he says, and yet they're not tempted to hastily split them into separate species. Why must we look at ourselves any differently? "A lot of the special treatment this controversy gets is just the fact that we're talking about humans," he says. "If this were a fruitfly dataset, there would be no controversy at all."
On that single point at least, both sides would heartily agree.
Ruth Flanagan is a contributing editor of EARTH magazine.