I have been fascinated with the research on the most recent common ancestor (MRCA) of human beings ever since I read the research of Joseph Chang et. al. that suggested that that person could have lived as recently as about 50 CE or so, around the time of Jesus. (See here, here, and here for my previous posts on this topic.)
Chang was doing a statistical, not biological, analysis using a model of interbreeding where our MRCA could be traced back through any lineage but there is another way to do the tracking and that is by following just Y-chromosome only or the mitochondrial DNA only. Since the former is transmitted only through males, you would be finding the MRCA by going back through only the male lineage to reach the individual (dubbed ‘Y-chromosome Adam’) while the latter is transmitted only by females so you would be following only the female lineage and reach ‘mitochondrial Eve’. Naturally, the dates for the MRCA would get pushed back even further than a lineage in which the sex of the ancestors was ignored.
In Richard Dawkins’s book The Ancestor’s Tale (p. 52-55), he says that this ‘Adam’ would be expected to be around 60,000 years ago while ‘Eve’ would be around 140,000 years ago. But now more recent research using the sequencing of the DNA of the entire Y-chromosome suggests that Adam lived between 120,000 and 156,000 years ago and a similar analysis says that Eve lived between 99,000 and 148,000 years ago, contradicting the earlier idea that the Eve appeared earlier than Adam. Now they could have been contemporaneous.
The paper can be seen here and here is its abstract:
The Y chromosome and the mitochondrial genome have been used to estimate when the common patrilineal and matrilineal ancestors of humans lived. We sequenced the genomes of 69 males from nine populations, including two in which we find basal branches of the Y-chromosome tree. We identify ancient phylogenetic structure within African haplogroups and resolve a long-standing ambiguity deep within the tree. Applying equivalent methodologies to the Y chromosome and the mitochondrial genome, we estimate the time to the most recent common ancestor (TMRCA) of the Y chromosome to be 120 to 156 thousand years and the mitochondrial genome TMRCA to be 99 to 148 thousand years. Our findings suggest that, contrary to previous claims, male lineages do not coalesce significantly more recently than female lineages.
Of course, it should go without saying (but sadly needs to be said anyway) that this has nothing to do with the biblical story of Adam and Eve but those were merely the catchy names scientists gave to these ancestors. The fact that they existed earlier than 6,000 years ago will dampen the enthusiasm for biblical literalists but the fact that they may have existed contemporaneously may encourage those who think that while the Genesis story is a metaphor, it did represent reality in some way.