SAN FRANCISCO – "Adam," humankind's most-common male ancestor, is from an older era than once thought, living about the same time as genetic "Eve," a study found.
Using the complete strand of DNA that determines male sex, researchers have determined that Y Chromosome Adam lived 120,000 to 156,000 years ago, overlapping with Mitochondrial Eve, who probably lived 99,000 to 148,000 years ago, according to a recent paper published in the journal Science. Researchers previously thought Adam had lived 50,000 to 150,000 years ago.
The new data provide a richer picture of the outlines of human history, helping scientists more precisely understand the evolutionary tree. Previous efforts to date a common ancestor didn't use the whole Y chromosome, leaving undetected the rare variations that help define commonality with past generations.
"When we put it together, we realized we had the very best map at the time of human genetic variation," Carlos Bustamante, a genetics professor at Stanford University and a study author, said in a telephone interview. "And when we started looking at this classic question, we were getting an answer that was different than before."
The study analyzed the Y chromosome for 69 men from nine populations, and traced backward to the time of man's presumed beginnings. Previous estimates for Adam were based on a smaller amount of data and less-diverse population, Bustamante said.
Y chromosomes that carry the same mutations share a common male ancestor in the past. It's possible to determine how far back that ancestor was by looking at how many mutations differ between the chromosomes: The more mutations that aren't shared, the longer ago the common ancestor lived.
The common ancestor in the study probably isn't the first, said Jennifer Hughes, a researcher with the Whitehead Institute for Biomedical Research in Cambridge, Mass. Rather, he's one of probably thousands of very successful and very lucky fathers, whose offspring were also successful. He just happens to be easy to track, thanks to the qualities of these portions of DNA, Hughes said in a telephone interview.
