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Yes, yes, and no.

There is in fact a single woman who is the most recent direct female ancestor of everyone alive today. She is known as Mitochondrial Eve. Daniel Dennett, in his book Darwin's Dangerous Idea, demonstrated her necessary existence as follows:

"Mitochondrial Eve is the woman who is the most recent direct ancestor, in the female line, of every human being alive today. People have a hard time thinking about this individual woman, so let's just review the reasoning. Consider the set A, of all human beings alive today. Each was born of one and only one mother, so consider next the set, B, of all the mothers of those alive today. B is of necessity smaller than A, since no one has more than one mother, and some mothers have more than one child. Continue with set C, of mothers of all those mothers in set B. It is smaller still. Continue on with sets D and E and so forth. The sets must contract as we go back each generation. Notice that as we move back through the years, we exclude many women who were contemporaries of those in our set. Among these excluded women are those who either lived and died childless or whose female progeny did. Eventually, this set must funnel down to one-- the woman who is the closest direct female ancestor of everybody alive on earth today. She is Mitochondrial Eve, so named (by Cann et. al 1987) because since the mitochondria in our cells are passed throug the maternal line alone, all the cells in all the people alive today are direct descendents of the mitochondria in her cells."

The same reasoning can be applied to the male lineage.

Since there is a Mitochondrial Eve, it logically follows that for any two people alive, they share a common female grand-eve. She may be Mitochondrial Eve, or more likely, a female descendent of Mitochondrial Eve.

Did your and my Grand Eve and Grand Adam necessarily know each other? No. If our Grand Eve is Mitochondrial Eve, almost certainly not. Our Grand Adam may have been born centuries before or after Mitochondrial Eve.

Why?

Let's say our Grand Eve-- let's call her Evelyn-- lived in Germany five hundred years ago. Evelyn must have had at least two daughters (if she had only one, that daughter would be our Grand Eve). One daugther's lineage eventually produced me, the other eventually produced you. Did our Grand Adam know Evelyn? It's possible, but by no means necessary. In this example I make the assumption you have German blood on your Mother's side stemming from the 16th century. So you could be 100% German. But my father is Chinese. If you don't have Chinese blood, we could still share a Grand Eve as recent as Evelyn, but our Grand Adam might date back tens of thousands years to a tribe living it what is now the Middle East.

Scientify American had an interest Ask The Expert recently that explores the most recent ancestor that you or I might share with our more remote relatives- like apes, tetrapods and fungi.

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