There is one important point that needs consideration.
They used mitochondrial DNA instead of nuclear DNA. Nuclear DNA is inherited from both parents through recombination, mitochondrial DNA is inherited only from the mother.
Thus in mitochondrial DNA the diversifying effect of mutation is countered by the homogenising effect of matrilineal lineages dying out (a female who only has male offspring cannot pass on mitochondrial DNA but will pass on nuclear DNA). This is the effect that causes a mitochondrial Eve
(Note that this paper is pretty bad news for Faith. All variation in human mitochondrial DNA would have to be mutation since the creation of Eve.)