MRCA & Mitochondrial Eve
MRCA, or Most Recent Common Ancestor, is usually used to discuss the genealogy of organisms within a given species. Essentially, the MRCA of all living humans (homo sapiens) would be an individual from whom we are all descended – not necessarily the first human being, but the most recent to have been a source of genetic material to all who have followed. Mitochondrial Eve is humanity’s theoretical matrilineal most recent common ancestor – that is, the most recent when traced back only by maternal parentage.
Her counterpart, traced back only by paternal parentage, is called Y-chromosomal Adam. The two are named after the Biblical first woman and man, respectively. However, it is important to note that the namesakes were not the first, nor were they the only living people in their time (they may have lived within a large population of humans, and are simply the only to be the ancestor of all currently living humans).
In fact, Mitochondrial Eve and Y-chromosomal Adam did not even live during the same time period – the former dates to approximately 140,000 years ago, whereas the latter may have lived anywhere from 60,000 to 90,000 years ago. The other half of their names derives from the method used to find them. Men pass on their genes to male children through the Y-chromosome, which allows male and female ancestry to be easily distinguished. On the other hand, X-chromosomes in female children are inherited from both the mother and father. Therefore, in order to derive the maternal line, researchers use DNA from mitochondrial organelles (mtDNA), which is inherited uniquely from the mother.
One of the most controversial discoveries about Mitochondrial Eve was that she most likely lived in Africa. This is often taken to support the Out-of-Africa hypothesis, which believes that all modern humans evolved in and originated from Africa; however, this revelation conflicted with the prevalent Euro-centric view of man’s origins. After criticism of the original study’s methodology, a more recent trial was undertaken in order to correct the mistakes, and achieved similar results (an African origin within 172,000 ± 50 000 years). To date, Mitochondrial Eve and Y-chromosomal Adam remain the most accurate examples of human MRCAs.