WASHINGTON, Aug. 1 (Xinhua) -- The most recent common ancestors to females and males, "Eve" and "Adam," appeared on the planet roughly around the same time, U.S. researchers said Thursday.
A study led by the Stanford University School of Medicine, which appeared in the journal Science, determined that our male most recent common ancestor (MRCA) known as Y-chromosomal "Adam" lived 120,000 and 156,000 years ago, overlapping with Mitochondrial "Eve" who lived 99,000 and 148,000 years ago.
Initial estimates for the male MRCA ranged from between 50,000 to 115,000 years ago.
The researchers compared the sequences of Y-chromosome, which is passed only from father to son, among 69 men from nine globally distinct regions, including some that have only recently been available for study. Regions represented included Namibia, the Democratic Republic of Congo, Gabon, Algeria, Pakistan, Cambodia, Siberia and Mexico.
The researchers identified about 11,000 differences among the sequences, which enabled them to establish phylogenetic relationships and timelines among the sequences "with unprecedented accuracy."
They found that the most recent male common ancestor with a Y- chromosome appeared on the planet between 120,000 to 156,000 years ago.
By applying the same analytical techniques to mitochondrial DNA, which was passed only from mother to daughter, the researchers also calculated that mitochondria and the modern maternal lineage originated sometime between 99,000 and 148,000 years ago.
"Previous research has indicated that the male MRCA lived much more recently than the female MRCA," said Carlos Bustamante, professor of genetics at the Stanford University and senior author of the study. "But now our research shows that there's no discrepancy."
Despite the "Adam" and "Eve" monikers, which evoke a single couple whose children peopled the world, it is "extremely unlikely " that the male and female MRCAs were exact contemporaries, the researchers said.
They weren't the only man and woman alive at the time, or the only people to have present-day descendants, the researchers said.
These two individuals simply had the good fortune of successfully passing on a portion of their genomes to the vast expanse of humanity, through the millennia to most of us, while the corresponding sequences of others have largely died out due to natural selection or a random process called genetic drift, according to the study.