TUCSON, Ariz. (CBS Charlotte) — Researchers make a stunning find after analysis of a rare African American Y chromosome reveals that the male gene is much older than originally thought.
Geneticists from the University of Arizona made the discovery after a South Carolina man’s DNA sample predates the age of the oldest known anatomically modern human fossils.
“Our analysis indicates this lineage diverged from previously known Y chromosomes about 338,000 ago, a time when anatomically modern humans had not yet evolved,” Michael Hammer, associate professor in the University of Arizona’s department of ecology and evolutionary biology, told UA News. “This pushes back the time the last common Y chromosome ancestor lived by almost 70 percent.”
The original modern human fossil record was thought to be 200,000 years old before this recent finding.
The study published in The American Journal of Human Genetics states that this points “to the importance of considering more complex models for the origin of Y chromosome diversity.”
The DNA sample originally stumped the National Geographic Genographic Project when they could not find genetic markers used to assign lineages to known Y chromosome groupings. The sample was then sent to Family Tree DNA which determined that this man’s DNA had branched from the Y chromosome tree.
“The most striking feature of this research is that a consumer genetic testing company identified a lineage that didn’t fit anywhere on the existing Y chromosome tree, even though the tree had been constructed based on perhaps a half-million individuals or more. Nobody expected to find anything like this,” Hammer said.
This particular Y chromosome was traced to a particular African ethnic group in Cameroon called the Mbo.
“[T]he sample matched the Y chromosome DNA of 11 men, who all came from a very small region of western Cameroon,” Hammer said. “And the sequences of those individuals are variable, so it’s not like they all descended from the same grandfather.”
Despite the finding, Hammer warns that this should not be considered the “Y chromosome Adam.”
“There has been too much emphasis on this in the past,” Hammer said. “It is a misconception that the genealogy of a single genetic region reflects population divergence. Instead, our results suggest that there are pockets of genetically isolated communities that together preserve a great deal of human diversity.”
Hammer believes that the origin of the Y chromosome could be pushed back even further.
“It is likely that other divergent lineages will be found, whether in Africa or among African-Americans in the U.S. and that some of these may further increase the age of the Y chromosome tree.”