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By Root 1839 0

would be evidence of interbreeding, but that is not at all easy to prove, or disprove, from fossils. In 1999, archeologists in Portugal found the skeleton of a child about four years old that died 24,500 years ago. The skeleton was modern overall, but with certain archaic, possibly Neandertal, characteristics: unusually sturdy leg bones, teeth bearing a distinctive “shoveling” pattern, and (though not everyone agrees on it) an indentation at the back of the skull called a suprainiac fossa, a feature exclusive to Neandertals. Erik Trinkaus of Washington University in St. Louis, the leading authority on Neandertals, announced the child to be a hybrid: proof that modern humans and Neandertals interbred. Others, however, were troubled that the Neandertal and modern features weren't more blended. As one critic put it: “If you look at a mule, you don't have the front end looking like a donkey and the back end looking like a horse.”

Ian Tattersall declared it to be nothing more than “a chunky modern child.” He accepts that there may well have been some “hanky-panky” between Neandertals and moderns, but doesn't believe it could have resulted in reproductively successful offspring.*49 “I don't know of any two organisms from any realm of biology that are that different and still in the same species,” he says.

With the fossil record so unhelpful, scientists have turned increasingly to genetic studies, in particular the part known as mitochondrial DNA. Mitochondrial DNA was only discovered in 1964, but by the 1980s some ingenious souls at the University of California at Berkeley had realized that it has two features that lend it a particular convenience as a kind of molecular clock: it is passed on only through the female line, so it doesn't become scrambled with paternal DNA with each new generation, and it mutates about twenty times faster than normal nuclear DNA, making it easier to detect and follow genetic patterns over time. By tracking the rates of mutation they could work out the genetic history and relationships of whole groups of people.

In 1987, the Berkeley team, led by the late Allan Wilson, did an analysis of mitochondrial DNA from 147 individuals and declared that the rise of anatomically modern humans occurred in Africa within the last 140,000 years and that “all present-day humans are descended from that population.” It was a serious blow to the multiregionalists. But then people began to look a little more closely at the data. One of the most extraordinary points—almost too extraordinary to credit really—was that the “Africans” used in the study were actually African-Americans, whose genes had obviously been subjected to considerable mediation in the past few hundred years. Doubts also soon emerged about the assumed rates of mutations.

By 1992, the study was largely discredited. But the techniques of genetic analysis continued to be refined, and in 1997 scientists from the University of Munich managed to extract and analyze some DNA from the arm bone of the original Neandertal man, and this time the evidence stood up. The Munich study found that the Neandertal DNA was unlike any DNA found on Earth now, strongly indicating that there was no genetic connection between Neandertals and modern humans. Now this really was a blow to multiregionalism.

Then in late 2000 Nature and other publications reported on a Swedish study of the mitochondrial DNA of fifty-three people, which suggested that all modern humans emerged from Africa within the past 100,000 years and came from a breeding stock of no more than 10,000 individuals. Soon afterward, Eric Lander, director of the Whitehead Institute/Massachusetts Institute of Technology Center for Genome Research, announced that modern Europeans, and perhaps people farther afield, are descended from “no more than a few hundred Africans who left their homeland as recently as 25,000 years ago.”

As we have noted elsewhere in the book, modern human beings show remarkably little genetic variability—“there's more diversity in one social group of fifty-five chimps than in the entire