Who is Mitochondrial Eve? What is the Eve gene?

What "Mitochondrial Eve" actually means

In human genetics, Mitochondrial Eve is the matrilineal most recent common ancestor of all living humans. She is defined as the most recent woman from whom all living humans descend in an unbroken line purely through their mothers, and through the mothers of those mothers, back until all lines converge on one woman.

The woman who held this title is believed by some to have lived about 150,000 years ago in what is now Ethiopia, Kenya or Tanzania. That date is calculated using the molecular clock technique, which correlates elapsed time with observed genetic drift.

The name "Eve" was chosen by researchers as a reference to the biblical figure, though the lead biochemist on the original research, Allan Wilson, preferred the term "Lucky Mother" and thought the use of the name Eve "regrettable."

What the Eve gene is

The "Eve gene" is not a single gene in the traditional sense. It is a popular shorthand for the specific type of DNA that makes this tracing possible: mitochondrial DNA, or mtDNA.

Mitochondrial DNA is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form cells can use. Think of mitochondria as the tiny power stations inside every one of your cells. They carry their own small strand of DNA, separate from the main DNA in the cell's nucleus.

Mitochondrial DNA is particularly useful for investigating recent genetic history because it mutates quickly (ten times more rapidly than nuclear DNA) and in humans is inherited solely through the female line, so it does not undergo recombination by crossing over. That last part is the key: because sperm contribute no mitochondria to a fertilized egg, the mtDNA in every living person came exclusively from their mother, who got it from her mother, and so on, in an unbroken maternal chain.

In 1987, a group of geneticists published a study in Nature examining the mitochondrial DNA taken from 147 people across all of today's major racial groups. They found that all modern humans descended from one of two branches in humanity's family tree: one consisting of nothing but African lineage, and another containing all other groups, including some African lineage.

The biggest misconception

Mitochondrial Eve was not the only woman alive in her time, and she was not the "first" woman.

One of the misconceptions of Mitochondrial Eve is that since all women alive today descended in a direct unbroken female line from her, she was the only woman alive at the time. Nuclear DNA studies indicate that the size of the ancient human population never dropped below tens of thousands. There were many other women around at Eve's time with descendants alive today, but somewhere in all their lines of descent there is at least one man, and men do not pass on their mothers' mitochondrial DNA to their children.

It is important to remember that we all carry the DNA of other women from Eve's era too. What is special about Eve is only mitochondrial DNA, which is transmitted only through women.

So what made her "Eve" is not that she was special in her lifetime. It's that she happened to be the one whose maternal line never broke. She represents an unbroken human chain of matrilineal inheritance, connected for millennia, because she is the only woman whose offspring survived every single generation long enough to make another generation.

Her male counterpart

Mitochondrial Eve is the female counterpart of Y-chromosomal Adam, the patrilineal most recent common ancestor. Y-chromosomal Adam is traced through the Y chromosome, which passes exclusively from fathers to sons. The two did not live at the same time, and neither is the "first" human in any literal sense.