A paper published last weekreported some fascinating news about humanity’s deep origins.
A primer: We all know about the Y chromosome and the X chromosome. Women carry two Xs. Men have an X and Y. Now, that’s the simple version; reality is a bit more complicated (and way more interesting!) when it comes to our sex-linked chromosomes.
The Y-Chromosome, basically, is passed from father to son intact. Occasionally, mutations occur, and these are also passed along. The mutations can be used to reconstruct human migrations across the planet, track the divergence between us and our cousin primates and hominids (both living and extinct), and locate the common ancestor of all human males on Earth. Colloquially, this man is known as “Y-Chromosomal Adam,” from the progenitor named in the creation myth held by the Abrahamic religions.
Now, like “Mitochondrial Eve”, Y-Chromosomal Adam was not a single individual. It simply refers to a man who had at least two sons whose unbroken lineage has survived to the present day. If the lineage dies out, the title shifts forward. Also, see pixxer's comment below. This, incidentally, is something the rebooted Battlestar Galactica got ever so wrong in its series finale, although it’s nice to joke that we’re all part robot. Thus, this person can change through time, and the time Y-Chromosomal Adam has lived has been revised---he either lived 142,000 years ago or roughly 70,000 years ago. There are events that’d cause this:
-Discovery of new mutations that’d cause the human family tree to get rearranged,
-Revision of the Y-Chromosome mutation rate which would change the estimate of the time this man lived,
-Further sampling of Y-chromosomes which discover previously unknown divergent lines, which could cause the lineages to converge on an individual who lived further back in time. This is indeed what has happened.
An African-American man's family submitted his DNA for commercial genealogical analysis by Family Tree DNA. One of the unique and sad challenges that we in the Diaspora have is that our ancestors were stolen from our homelands. Unlike others who can trace back to Europe rather easily, we simply can’t. We run into walls -a good portion of my tree, especially on my mother’s side, is stuck at 1870 for concrete data and I haven’t yet had the heart to dive into slave records, and some of us are hampered by incorrect family traditions that we’re perhaps part Native American despite no evidence for it. As a result, many of us have submitted our DNA to genealogical DNA companies, especially after Oprah popularized it, me included. These DNA tests only test direct ancestral lines, and not the entire tree, although “full tree” tests do exist now. Some of us have found disappointment. I, for example, found Europeans in both direct ancestral lines---the Y-DNA came from Scandinavia by way of Yorkshire, UK, and the mtDNA possibly from southern Europe. I admit disappointment but also fascination, as I discovered the concept of “outside families” in the Bahamas where my father’s entire family hails from and got a history lesson about the Viking invasions of Great Britain (the Y-DNA I carry apparently entered the UK about 1,000 years ago). I also learned that my surname is very rare, even in the part of the UK it originated, and the likelihood that I’m distantly related to someone with it is fairly good, regardless of what color they are now. The mtDNA result may be a bit off---when I get the funds I’ll have it tested more. It may well be directly from Africa after all.
Albert Perry's relatives simply wanted to know where in Africa his people hailed from. Now deceased, a relative of his submitted his DNA as part of a project.
Family Tree DNA could not figure out what was up. Mr. Perry’s Y-Chromosome was nothing that they’d ever seen. Further research determined that his Y chromosome is so distinct that it likely separated from all other Y-DNA lineages about 338,000 years ago. Further testing in a small village in Cameroon found a small number of men of the Mbo people still carry this DNA. What’s even cooler is that his Y-chromosome lineage separated from the rest of humanity long before our species appeared—about 195,000 years ago, according the dating of the first anatomically modern human fossils.
This suggests that sometime in the last 195,000 years, modern humans interbred with our human-like cousins, who we did share the planet with for quite some time and there’s evidence for that in fossils found not far from the village where Albert Perry’s Y-DNA also exists.
How neat and how awesome for Mr. Perry and his family, who likely just wanted to find where in Africa his people originated, to discover that he had the world’s most ancient modern human DNA. And how neat and how awesome to see how deep our story, as a species, goes back in time.
The actual paper is here.