Mitochondrial Eve

A comparison of the mitochondrial DNA of humans from many races and regions suggests that all of these DNA sequences have evolved molecularly from a common ancestor sequence. Under the assumption that an individual inherits mitochondria only from his or her mother, this finding implies that all living humans descend from one woman--possibly one pre-human woman--who researchers have dubbed Mitochondrial Eve. Based on the molecular clock technique, Eve is believed to have lived roughly 150 000 years ago.

Eve was not the sole living female of her day. Researchers believe as many as 20 000 individuals of Eve's species may have lived at the same time as her. But of the females of her day, only Eve produced an unbroken line of daughters that persists today. This is assumed to be an effect of chance rather than selection. Essentially, the hypothesized process by which all lineages but one disappear is the same as genetic drift. As with genetic drift, the process is much slower and much less likely to reach completion in a large population than in a small one. If Eve had lived among a million or a billion other females, it is very unlikely that all humans alive today could trace their descent to Eve (or to one female contemporary of Eve's).

The observation that the mitochondria of living humans point to a common ancestor represents evidence that this ancestor lived in a much smaller breeding pool than humans live in today. This may be because the population in Eve's day passed through a bottleneck, or it may be that Eve lived only shortly after the migration or other isolation event that led to human speciation. Of the ancient human and hominid remains discovered so far, the oldest matching the bones of modern humans date from around the time that Eve lived.

On the other hand, the most recent common ancestor to father an unbroken line of males, "Y-chromosome Adam," appears to have lived only about half as long ago as Eve. This means that another bottleneck event besides the one surrounding Eve affected the human lineage after her. The fact that the bottleneck in Adam's day appears not to have produced also a matrilineal ancestor of all living humans--a more recent Eve, in other words--illustrates that the branching and disappearance of lineages depends on chance.

A recent challenge to the Eve theory has been the observation that the mitochondria of sperm are sometimes passed to offspring. Mitochondria may not be so pure a matrilineal marker as they were supposed when the theory was advanced.

Note that the concept of mitochondrial Eve is different from that of "African Eve," although anthropologists have hypothesized a connection.

The Japanese horror film and novel Parasite Eve use the Mitochondrial Eve theory as the basis for a fantasy about a scientist bringing his dead wife back by regenerating her liver cells, with disastrous effects.