Mitochondrial Eve is the name given by researchers to the woman who is the most recent common matrilineal ancestor of all living humans. We know about Eve because of mitochondria.
Naming Mitochondrial Eve after Eve of the Genesis creation story, has led to some misunderstandings among the general public. A common misconception is that Mitochondrial Eve was the only living female of her time — she was not (indeed, had she been, humanity would have probably become extinct). Many women alive at the same time as Mitochondrial Eve have descendants alive today. However, only Mitochondrial Eve produced an unbroken line of daughters that persists today — each of the other matrilineal lineages was broken when all the women in a particular matriarchal ancestry had only sons, or no children at all.
Simply put, Eve was a survivor. A maternal line can become extinct for a number of reasons. A soman may not have children, she may bear only sons, (who do not pass mtDNA to the next generation). She may fall victim to a catastrophic event (Volcanic eruption, landslide, flood, famine, etc), all of which have plagued humanity since the dawn of time.
After getting my DNA results back from the NGS my DNA goes all the way back to the Mitochondrial Eve, starting somewhere in or around the Olduvai gorge in Kenya, East Africa.
More on my DNA's particular journey in the next post.