Other Free Encyclopedias » Medicine Encyclopedia » Genetics in Medicine - Part 3 » Molecular Anthropology - Tracing Human Origins Through Genetic Data, Advantages Of Dna Comparisons, Caveats About Sequence Comparisons, Types Of Dna Comparisons

Molecular Anthropology - Mitochondrial Eve

chromosome genetic type woman time mother

In their study, Cann, Stoneking, and Wilson pointed out that the patterns of mitochondrial variations they saw suggested that all the mitochondria of all living groups could be traced back to a single woman who lived in Africa approximately 200,000 years ago. Many people at the time of the original study and since have misinterpreted the results to claim there was a single female ancestor for all modern humans, dubbed "Eve." It is true the study showed that the mitochondrial DNA in all living humans probably derives from this single woman. However, our nuclear DNA certainly does not derive exclusively (perhaps even at all) from this woman, and the thirty thousand or more genes in our nuclear DNA are far, far more important in determining our characteristics than the thirty-seven mitochondrial genes. Because of recombination, our nuclear DNA cannot be traced back to any single person. Rather, it is an amalgam of countless ancestors through time.

Mitochondrial Eve was also not the first modern human woman, nor the only woman in existence at the time she lived. She was not even the only woman in her local population; it is estimated that Eve was one of about 10,000 people in her population. There was really nothing particularly special about her, except that, by chance, the descendants of her mitochondria happen to have ended up in the cells of every living human. Even this, which sounds remarkable, is pretty much what we should expect from small populations.

To understand why, consider four couples, each of which has two children. Remember that mitochondria are passed from the mother to each child. One couple has two boys. Each boy inherits the mother's mitochondria, but neither passes them on to his children. The mother's mitochondrial type thus becomes extinct in one generation. Two of the couples have a boy and a girl, while the fourth has two girls. These four daughters go on to have children of their own, each with the same distribution according to sex. Whenever a family has only boys, a mitochondrial type becomes extinct. Any time a family has only girls, the mitochondrial type handed down from the mother becomes more common in the next generation. In a small population, over time, it is highly likely that one type will become most prevalent, ultimately becoming the one type found in all the members of the population. Looking back, we would give the name "Eve" to the original mother of that line of mitochondrial genetic inheritance.

A similar phenomenon occurs with the Y chromosome, for exactly the same reasons: Any family with only girls extinguishes that Y chromosome type. The "Y chromosome Adam" lived 60,000 to 150,000 years ago. There is no reason to expect that "Y chromosome Adam" would know "mitochondrial Eve"; indeed, even without the dates to make it impossible, it would be a remarkable coincidence if they had.

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