Y and mtDNA are not Adam and Eve: Part 2 – What it means to be the Most Recent Common Ancestor?
9th August 2013
1. One person (or two people) did not have the ancestral state of all of our DNA.
The person whose cells housed the common mtDNA ancestor (or Y ancestor) also had all of the other chromosomes (1-22 and X), but did not house the common ancestor of each of these chromosomes. These non-sex chromosomes are a lot more complicated. This touches on why it is also misleading to refer to the common ancestor of genetic “males” versus “females.” Genetic females are not only their mtDNA – we also have 22 non-sex chromosomes, and two X chromosomes! Genetic males are not only their Y (and mtDNA), they also have 22 non-sex chromosomes and one X chromosome! Because the non-sex chromosomes (autosomes) can swap DNA, and are inherited through both the sperm and the egg, they much more complicated history than the Y and mtDNA.2. A lower bound, not a point estimate.
Tracing back to the common ancestral mtDNA or the common ancestral Y chromosome does not tell us when anatomically modern humans arose. We can estimate the TMRCA, or the Time to the Most Recent Common Ancestor, but this mtDNA surely existed much further back in time.