Who is "Mitochondrial Eve?"

In the Biblical account, after the first humans were banished from Eden, Adam named his wife “Eve,” a name symbolizing she would become “mother of all the living” (Gen. 3:20).  Our mitochondrial DNA also reveals that we descend from a common female ancestor, and hence we colloquially call this ancestor “Mitochondrial Eve.”  Who are we talking about when we use the term “Mitochondrial Eve?” 

A 1988 article by Newsweek is among the
first popular articles to discuss
Mitochondrial Eve. 

Mitochondrial Eve is defined by geneticists as the most recent matrilineal ancestor of all humans alive today.  Since mitochondrial DNA is inherited directly from one’s mother, uncombined with any DNA of a male ancestor, it can only change due to mutations.  Those mutations are traceable, through maternal ancestry.  The mutations are nested, in that a certain mutation, let’s name it “B” always occurs when “A” is also present.  However, the opposite is not true: “A” can be present without “B.” Therefore one can determine which mutations occurred more recently and which ones are more ancient.   In this example “A” is older than “B.”  This nesting pattern is the scientific basis behind the study of cladistics.

As we trace mtDNA haplotypes back through time we encounter less and less human genetic variation, and ultimately converge to a single, common matriarchal ancestor.  My haplotype T2b2, descends in an unbroken chain from T2b > T2 > T > JT > R2’JT > R > N > L3, and then  through several steps in haplogroup L back to Mitochondrial Eve.  Every person’s tree will lead back to Mitochondrial Eve. Although we cannot pinpoint an exact generation or date in which the maternal convergence of all humans occurred, it was sometime around 10,000 generations ago, approximately 200,000 years ago.  However, don’t get caught up on this convergence as a specific “event” in its own time. This convergence only has meaning from the perspective of our modern time (in this generation). Here’s why:

Think of it this way.  The set of humans presently alive is approximately 7.3 billion. This large number is only a subset of the number of humans who have ever existed.  If, say 500 years ago, we were able to take DNA samples from across the ethnic groups of humans alive, we would find lineages that have since become extinct, particularly among indigenous peoples whose lineages have been exterminated by the impact of colonialism.  Some of those extinct lineages, particularly in Africa, would descend from the basal branches of our current tree. Therefore the “Mitochondrial Eve” of 500 years ago was an earlier ancestor of the “Mitochondrial Eve” we have today.  The trunk of the tree would need to be extended back further to take into account the lineages that went extinct.  The female ancestor that unites all people living 500 years ago would have herself lived earlier than Mitochondrial Eve, as defined today.

We should also note that basal lineages are no closer to our ancestors than ourselves.  We are all the same distance, both in generations and time, from our early ancestors, whether we are African, Asian, European or Native American.  There is more human genetic diversity in Africa, so it is clear that continent is our origin, however it is a misrepresentation to believe that basal branches have a closer connection to our ancestors.

Typical male response to the bigger questions of life?

In no case is Mitochondrial Eve the sole human female in existence. On the East African prairie 200,000 years ago, there were many interrelated tribes of humans.  Eve is simply the one female from whom we all descend via an unbroken maternal lineage.  Everyone descends from mitochondrial Eve the same way, through their mother.  While many of her contemporary friends and enemies were also our ancestors, we descend from the others in a complexity of paths via fathers and mothers.

Scientifically, the maternal ancestor of all humans alive today is not the first female human that ever existed, so the name “Mitochondrial Eve” is a bit of a misnomer.  The “first human” is not easy to define because DNA mutations proceed back through time eventually to converge with a similar progression arising from the chimpanzee branch of the tree of life. At what time and at what place along this branch can we define the first human?  That depends on our definition of human. But first, where do the Neanderthals fit in?  That's the subject of the next blog.