The problem of our common mitochondrial mother.

It has been suggested that the mitochondrial DNA (mtDNA) of all present-day human beings stems exclusively from one woman who lived about 200000 years ago in Africa; examination of the problem by the mathematical theory of random walks supposedly renders alternatives very unlikely. However, a statistical argument first used by Fisher indicates that this hypothesis is untenable, at least if the assumptions made by previous workers are accepted. All present-day mtDNA might go back to one individual, especially if small populations and population bottlenecks with very small numbers of reproducing individuals are assumed; nevertheless, this phase in the evolution of Homo sapiens probably dates back considerably more than 200000 years.