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The genetic Adam & Eve

Genetic genealogists often talk about Y-Adam and mt-Eve. What do they mean?

Introducing Y-Adam

We call him "Y-Adam", the genetic counterpart to the biblical Adam. All living human males descend from one man who lived. probably in Africa, some hundreds of thousands of years ago.

The most recent finding is that he may have been roaming the veldt as much as 338 kya; the lowest estimate is 120 kya. That's a minimum of about 5,000 generations and a maximum of about 15,000 generations -- either way, a very long time.

The difference between estimates is largely due to the recent finding of a haplogroup A00 man. (Haplogroup A, then A0, was previously believed to be at the "root" of the phylogenetic
Y-tree.)

Molecular Clock

Scientists arrive at the these estimates by tracing the ages of the various mutations that have occurred in the Y chromosome and, essentially, adding them up. The mutations don't happen on a regular schedule, the clocks ticks randomly. But over this long a period, the timing averages out to a fairly small error.

In short, the more variations in present haplotypes and mutations from the inferred original haplotype, the older the most recent common ancestor has to be.

Was he alone?

Unlike biblical Adam, Y-Adam was probably not the only male human fathering children in his time. He had companions around to do manly stuff with -- hunt, retire to the "man-cave", compare notes on spear-making, gripe about honey-do lists.

It's simply that the direct paternal lineages of the others have gone extinct and they now have no living descendants with their (mutated) Y chromosomes. On the other hand, we probably are carrying the autosomal DNA of some of these men around in our cells today.

Introducing mtDNA Eve

The genetic counterpart to biblical Eve is mt-Eve, who is our great-to-the-umpteenth-power- grandmother. All living humans are descended from her through their maternal lineages.

There is another kind of DNA that is passed down only through the direct maternal line; it is contained in our mitochondria. These are little energy bundles of DNA, outside the cell nucleus. They have their own separate genome and are inherited by both males and females from their mothers.

Molecular Clock

The mtDNA clock works like the Y-chromosome clock, except that it ticks a bit more slowly. mtDNA is more stable than Y-DNA and less subject to mutations.

Was she alone?

Nope, mt-Eve undoubtedly had companions to help look after the kids, gather firewood, and gripe about how the lazy men never finished the honey-do llsts.

But those other women's mtDNA has gone extinct too.