Here are a couple of links:
Mitochondrial Eve (mt-mrca) is the name given by researchers to the woman who is defined as the matrilineal most recent common ancestor (MRCA) for all currently living humans. Passed down from mother to offspring, her mitochondrial DNA (mtDNA) is now found in all living humans: every mtDNA in every living person is derived from hers. Mitochondrial Eve is the female counterpart of Y-chromosomal Adam, the patrilineal most recent common ancestor, although they lived at different times.
She is believed to have lived about 140,000 years ago in what is now Ethiopia, Kenya or Tanzania. The time she lived is calculated based on the molecular clock technique of correlating elapsed time with observed genetic drift.
Mitochondrial Eve is the most recent common ancestor (MRCA) of all humans via the mitochondrial DNA pathway, not the unqualified MRCA of all humanity. All living humans can trace their ancestry back to the MRCA via at least one of their parents, but Mitochondrial Eve is defined via the maternal line. Therefore, she necessarily lived at least as long, though likely much longer, ago than the MRCA of all humanity.
The existence of Mitochondrial Eve and Y-chromosomal Adam does not imply the existence of population bottlenecks or a first couple. They each may have lived within a large human population at a different time.
Because the rate of mitochondrial genetic mutation is slow, it can be used as a clock to turn back time to a period before the mutations had crept in. When mitochondrial DNA from certain populations in Africa are sampled, they can be compared with European mitochondrial DNA. The mutation difference between the two populations can then be compared, and a 'clock' can be produced, enabling the rate of mutation in mitochondria to be established. This produces a time-scale which indicates when modern Europeans first left Africa.
The genetic survey that produced the whole Mitochondrial Eve scenario didn't just sample Africans and Europeans – it sampled genes from people all over the planet. When mitochondrial DNA was compared, the survey discovered a startling result. Fundamental similarities in mitochondrial DNA in living humans suggested that we all contain genetic material from a single woman who was living in Africa around 200,000 years ago.
I have been quiet, but I have not left the woh family....