Who Is Mitochondrial Eve?

Mitochondrial DNA (mtDNA) are just a few genes that exist on the outside of a human ovum (the egg inside a woman waiting to be fertilised by a sperm). Mitochondrial DNA can only be passed down from a female to her children (so you inherit it only from your mother).  

Genes in mtDNA mutate (randomly change) at a fairly predictable (and slow) rate.  This makes it possible to guess when all present mtDNA lines converge; to trace back to a female ancestor from whom all women presently living on Earth descend.  This genetic mother Eve lived 200,000 years ago in Africa.

Well, That's how it is as long as we think we've sampled all the mtDNA on Earth.  Since that's impossible, the idea that all mtDNA in humans living today comes from a single woman alive 200,000 years ago seems less certain.  What is better accepted is the idea there must have been a genetic bottleneck, when the human population got down to relatively few people (less than 1000, maybe) at around 200,000 years ago.  That would explain why seemingly one woman is grandmother to us all not so long ago (relatively) in human evolution.