Humans are much older than scientists formerly thought. The male Y chromosome in Homosapien humans is not 100,000 years as previously reported. No, it's older than 338,000 years, just as old as Neanderthals. The discovery and University of Arizona (UA) analysis of an extremely rare African American Y chromosome push back the time of the most recent common ancestor for the Y chromosome lineage tree to 338,000 years ago.
This time predates the age of the oldest known anatomically modern human fossils. A newly discovered Y chromosome places the most recent common ancestor for the Y chromosome lineage more 100,000 years before the oldest known anatomically modern human fossils.
Check out the original study's abstract, "An African American Paternal Lineage Adds an Extremely Ancient Root to the Human Y Chromosome Phylogenetic Tree." The study's results are published in the February 28, 2013 issue of the American Journal of Human Genetics.
Scientists discovered the oldest known genetic branch of the human Y chromosome
University of Arizona (UA) geneticists have discovered the oldest known genetic branch of the human Y chromosome – the hereditary factor determining male sex. The new divergent lineage, which was found in an individual who submitted his DNA to Family Tree DNA, a company specializing in DNA analysis to trace family roots, branched from the Y chromosome tree before the first appearance of anatomically modern humans in the fossil record.
This shows that humans were around more than a quarter of a million years ago, not that the man carries the Y chromosome (his earliest founding father) of another type of hominid. It's a modern human Y chromosome, found in people today and had previously existed 338,000 years ago when father passed that same Y chromosome on from one son to the next across generations until the present day.
"Our analysis indicates this lineage diverged from previously known Y chromosomes about 300,000 ago, a time when anatomically modern humans had not yet evolved," says Michael Hammer, in the March 4, 2013 news release, Human Y chromosome much older than previously thought. Dr. Hammer is an associate professor in the University of Arizona's department of ecology and evolutionary biology and a research scientist at the UA's Arizona Research Labs. "This pushes back the time the last common Y chromosome ancestor lived by almost 70 percent."
Looking for the earliest common Y chromosome human ancestor
Unlike the other human chromosomes, the majority of the Y chromosome does not exchange genetic material with other chromosomes, which makes it simpler to trace ancestral relationships among contemporary lineages. If two Y chromosomes carry the same mutation, it is because they share a common paternal ancestor at some point in the past. The more mutations that differ between two Y chromosomes the farther back in time the common ancestor lived. Humans were around hundreds of thousands of years earlier than most scientists ever thought.
Originally, a DNA sample obtained from an African American living in South Carolina was submitted to the National Geographic Genographic Project. When none of the genetic markers used to assign lineages to known Y chromosome groupings were found, the DNA sample was sent to Family Tree DNA for sequencing. Fernando Mendez, a postdoctoral researcher in Hammer's lab, led the effort to analyze the DNA sequence, which included more than 240,000 base pairs of the Y chromosome.
Hammer says in the news release, Human Y chromosome much older than previously thought, "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."
How the prehistoric hominids differed from people around today
About 300,000 years ago falls around the time the Neanderthals are believed to have split from the ancestral human lineage. It was not until more than 100,000 years later that anatomically modern humans appear in the fossil record. They differ from the more archaic forms by a more lightly built skeleton, a smaller face tucked under a high forehead, the absence of a cranial ridge and smaller chins.
Hammer said the newly discovered Y chromosome variation is extremely rare. Through large database searches, his team eventually was able to find a similar chromosome in the Mbo, a population living in a tiny area of western Cameroon in sub-Saharan Africa.
Similar chromosomes exist in a tiny area of western Cameroon
"This was surprising because previously the most diverged branches of the Y chromosome were found in traditional hunter-gatherer populations such as Pygmies and the click-speaking KhoeSan, who are considered to be the most diverged human populations living today," Hammer says in the news release.
"Instead, the sample matched the Y chromosome DNA of 11 men, who all came from a very small region of western Cameroon," Hammer explains in the press release. "And the sequences of those individuals are variable, so it's not like they all descended from the same grandfather."
Hammer cautions against popular concepts of "mitochondrial Eve" or "Y chromosome Adam" that suggest all of humankind descended from exactly one pair of humans that lived at a certain point in human evolution. "There has been too much emphasis on this in the past," he 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."
Genetically isolated communities preserve more human diversity
Still, Hammer said, "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." He adds, according to the news release, "There has been a lot of hype with people trying to trace their Y chromosome to different tribes, but this individual from South Carolina can say he did it."
The study came about by combined efforts of a private business, Family Tree DNA, the efforts of a citizen scientist, Bonnie Schrack, and the research capabilities at the University of Arizona. Mike Hammer, PhD is Family Tree DNA's Chief Scientist, and member of the Scientific Advisory Board.
A Biotechnology Research Scientist at the University of Arizona with appointments in the Department of Anthropology and the Department of Ecology and Evolutionary Biology, as well as Director of the Genomic Analysis and Technology Core facility, Dr. Hammer received his PhD in Genetics from the University of California at Berkeley and was a post-doctoral fellow at Princeton and Harvard Universities.
Comments