Because all modern humans are genetically related (as members of the same species), it follows that we descended from a common ancestor. In 1987 a group of scientists claimed to have identified this ancestor as a Homo sapiens sapiens woman living in Africa about 200,000 B.P.1
Since then, however, other scientists have questioned this conclusion, pointing out that the research relies heavily on assumptions—which may be inaccurate—about the rate of natural mutation and the length of a generation.2 Other scientists have criticized the basic methodology of the DNA studies. They note that the order in which the data were entered into the computer affected the outcome, and that although each computer run produced several possible results—almost identical in terms of probability, but very different in their implications—only one of these alternatives was reported.3
The genetic studies have continued, however, and so have the warnings about relying too heavily on them. Recent tests compared Neandertal DNA and modern human DNA and concluded that Neandertals and modern humans are not related.4 However, critics of this study have noted that the DNA samples being compared are 20,000 or more years apart in age, and that the degraded and fragmentary Neandertal DNA had to be reconstructed in the laboratory before it could be used. There’s no way to know if the reconstructed sequences match the original DNA. Perhaps more significantly, almost all excavated Neandertal bones are contaminated by modern DNA (transferred from the hands of archaeologists and scientists).
Until these problems have been dealt with, any conclusions resulting from DNA studies will be highly speculative.
