The discovery of the oldest genetic branch of the human Y chromosome pushes the time of the last common ancestor of this lineage back 338,000 years. This time predates the age of the oldest known anatomically modern human fossils.
Geneticists at the University of Arizona have discovered this new divergent lineage that branched off the Y-chromosome tree before the appearance of anatomically modern humans. The study was based on a DNA sample from an African-American man who sent his DNA to Family Tree DNA Company for kinship analysis. The results of the study were published in the American Journal of Human Genetics.
The Y chromosome is the genetic factor that determines male gender. A distinctive feature of the Y chromosome is that most of it does not exchange genetic material with other chromosomes, making it easier to trace kinship between modern lineages. If two Y chromosomes carry the same mutation, it means that they shared a common ancestor in the paternal line. The more mutations that differ between two Y chromosomes, the earlier the common ancestor lived.
Analysis of a DNA sample from an African-American man showed that his Y chromosome diverged from previously known Y chromosomes about 338,000 years ago. This time predates the age of the oldest known anatomically modern human fossils. The discovery of this oldest genetic branch of the Y chromosome allows us to refine the timing of the last common ancestor of this lineage.
Importantly, this new genetic branch does not fit into existing Y-chromosome trees that have been constructed from multiple individuals. This makes the discovery even more surprising and unexpected. The researchers did not expect to find something like this.
Interestingly, about 300,000 years ago, when Neanderthals separated from human ancestors, anatomically modern humans had not yet appeared in the fossil record. They didn’t appear until 100,000 years after that. Anatomically modern humans differ from more archaic forms by having lighter bones, a smaller face tucked under a high forehead, no cranial crest, and smaller chins.
This discovery is of great importance to the study of human origins and evolution. It allows us to determine more precisely when the last common ancestor of the Y chromosome appeared and to trace the relatedness between different lineages of the Y chromosome. It also supports the hypothesis that anatomically modern humans emerged much later than Neanderthals separated.