Mitochondrial Eve
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[edit] Definition
Mitochondrial Eve is a person who is a common ancestor to all living humans on a female-only ancestral line. The fact that such a person existed is a logical consequence of the two facts: that humans are one species; and that no one has more than one (biological) mother. It should be stressed that “Eve” is an abstraction: as the most recent matrilineal common ancestor of living humans, it is possible for her identity to change, though it would now be necessary to kill off a large proportion of the human race in order to achieve this.
The phrase Mitochondrial Eve refers to the parts of the human cell called mitochondria. These have their own little piece of DNA, which is inherited exclusively from one's mother, unlike most other genes, which are affected by sexual recombination. This asexual transmission of mitochondrial DNA means that the only thing that can change the sequence from generation to generation is mutation, and so studies of these accumulated mutations allows geneticists to reconstruct the family tree of the human race, or at least its female members, and to say when and where Mitochondrial Eve lived. Recent studies put her at about 150,000 years before the present, in Africa.
Mitochondrial Eve's male counterpart is Y-Nuclear Adam: as Y chromosomes are passed down intact (but for mutation) from father to son, a similar genetic analysis can be made. The analysis for Mitochondrial Eve was done first, because in the early days of genetic analysis, a large tissue sample was required, and the placenta, being a large disposable bit of tissue, was very suitable for this purpose. For this reason Eve got, and continues to get, the bulk of the publicity.
[edit] Misconceptions
The name “Eve” leads to a number of misconceptions, by association with the Biblical “Eve”. The following misconceptions are not implied by the research at all:
- That “Eve” has no ancestry of her own. She indeed has ancestors, and all such females are also qualify as ancestors through the female line of all currently living humans, though only the one is the latest such.
- That “Eve” is the only common ancestor of the human race. There are probably thousands, or tens of thousands, of her contemporaries who were and millions of others both before and after her, including, of course, all of Eve's ancestors.
- That “Eve” was the only female in existence. She no doubt had many contemporaries, but she is the only one who is a common ancestor of all humans alive today by strictly matrilineal descent; the rest may or may not individually be ancestors of some of us; indeed, some her contemporaries may, like her, be ancestral to all living humans, just not matrilineally.
- That “Eve” knew “Adam”. There is no reason why they should have lived at the same time or in the same place; in fact we suspect that they lived some tens to hundreds of thousands of years apart in time, though they were both Africans.
- That all humans ever in existence were descended from “Eve”. She is an ancestor of all people alive today, and since that situation changes daily, her identity may also change. She may move from being the Mitochondrial Eve, the latest common female ancestor, to just one of Eve's ancestors as one of her descendants becomes the "latest".
These misconceptions have been used by Creationists as “scientific evidence” of the Genesis stories, or as evidence that the human race is younger than suggested by evolutionary models.
What is true is that if one follows back their female-only ancestral line, they will all encounter mitochondrial Eve. However, if one follows one’s ancestry along male and female lines, any one of thousands of other common ancestors will be encountered. “Eve”, then, enjoys no special status as the sole parent of the human race.
[edit] Idealized Example
The following highly idealized situation illustrates the concept, and may dispel erroneous conclusions.
We will represent the “race” as three generations of eight individuals each. Let S-Z represent the “current” generation.
We can make a couple of observations about the ancestry of the current generation. Every single one of them claims H as an ancestor, along a female-only line. H is therefore a common ancestor of the current generation, and corresponds with “Eve”.
[edit] Discussion of the Example
Does this mean that H is the sole female in her generation? Obviously not. There are three others shown in the diagram, as well as four males.
Does this mean that H is the lone female progenitor of the race? It does not. B, D, and F are also common female ancestors of everyone in the current generation.
Does this mean that all contemporaries of H led to descendants that died out? Again no. Every single one of them has eight descendants in the current generation.
Does this imply a primordial “Adam” who started the human family with H? Not necessarily. There are four males contemporary with H, and every one of them is a common ancestor of the current generation. Yet three of them have no relation to H whatsoever!
Does this show that all individuals are descended from H? Certainly not. Every generation except for the current one contains individuals not descended from H. Every one of these has descendants in the current generation.
Finally, does this mean that H and her generation are the “first” generation? There is nothing to suggest that this might be true. One could easily imagine connecting several of these diagrams together to continue the ancestry indefinitely.
