African Populations and the Evolution of

The proposal that all mitochondrial DNA (mtDNA) types in contemporary humans stem from a common ancestor present in an African population some 200,000 years ago has attracted much attention. To study this proposal further, two hypervariable segments ofmtDNA were sequenced from 189 people of diverse geographic origin, including 121 native Africans. Geographic speci-ficity was observed in that identical mtDNA types are shared within but not between populations. A tree relat-ing these mtDNA sequences to one another and to a chimpanzee sequence has many deep branches leading exclusively to African mtDNAs. An African origin for human mtDNA is supported by two statistical tests. With the use of the chimpanzee and human sequences to calibrate the rate of mtDNA evolution, the age of th