“They repeated this process for all 147 samples and, based on the differences in their mtDNA sequences, estimated how long one would need to look back to find a common ancestor. They looked back further and further, and the giant genetic tree they were drawing got narrower and narrower. Eventually Wilson and his students realized that the mtDNA sequences of all 147 individuals, who came from all over the world, could be mapped back to a single mtDNA sequence that belonged to a woman in Africa 200,000 years ago—and by extension, so could everyone else, from Buenos Aires to Beijing. The implication was not that she was the only woman on earth—there would have been other men and women who lived at the same time—but at some point the descendants of those other women stopped having daughters and their mitochondrial DNA died off, just as a last name might in a traditional patriarchal family without sons.”