Genealogy buffs know the thrill that comes with identifying ancestors further and further up the family tree. Reaching back through the sands of time to learn when, where and how our relatives lived is like a very personal treasure hunt.
Now geneticist Carlos Bustamante, PhD, and his colleagues have done something similar for our Y-chromosomal “Adam” and mitochondrial “Eve”: two individuals who have passed down a portion of their genomes to the vast expanse of humanity. These people are known as our most-recent common ancestors, or MRCAs. From our release:
“Previous research has indicated that the male MRCA lived much more recently than the female MRCA,” said Bustamante… “But now our research shows that there’s no discrepancy.” Previous estimates for the male MRCA ranged from between 50,000 to 115,000 years ago.
Bustamante’s research indicates the two MRCAs roughly overlapped during evolutionary time: from between 120,000 to 156,000 years ago for the man, and between 99,000 and 148,000 years ago for the woman. More from the release :
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. And they weren’t the only man and woman alive at the time, or the only people to have present-day descendants. These two individuals simply had the good fortune of successfully passing on specific portions of their DNA, called the Y chromosome and the mitochondrial genome, 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.
The researchers used high-throughput sequencing technology to sequence the Y chromosomes of 69 men from nine globally distinct regions. They identified about 11,000 differences among the sequences, which allowed them to determine phylogentic relationships and timelines with unprecedented accuracy. As graduate student and study co-author David Poznik described:
Essentially, we’ve constructed a family tree for the Y chromosome. Prior to high-throughput sequencing, the tree was based on just a few hundred variants. Although these variants had revealed the main topology, we couldn’t say much about the length of any branch — the number of variants shared by all of its descendants. We now have a more complete structure, including meaningful branch lengths, which are proxies for the periods of time between specific branching events.
Previously: Recent shared ancestry between Southern Europe and North Africa identified by Stanford researchers, Cracking the code of 1000 (make that 1092!) genomes and Blond hair evolved more than once-and why it matters
Photo by tup wanders