Science may have caught up with the Bible, which says that Adam and Eve are the ancestors of all humans alive today.
But in the scientists’ version, based on DNA analysis, “Adam,” the genetic ancestor of all men living today, and “Eve,” the genetic ancestor of all living women, seem to have lived tens of thousands of years apart.
How could this be?
Peter Underhill and colleagues at Stanford University in California have an explanation. “They had different molecular clocks,” Underhill said in a telephone interview. “Fewer men participated in reproduction than women did.”
Tracing Women to Earlier Time
His team, working with top geneticists across the United States, Europe, Israel and Africa, did a genetic analysis of DNA samples from the Y chromosomes of more than 1,000 men from 22 geographic areas and determined that their most recent common ancestor was a man who lived in Africa around 59,000 years ago.
Only men have Y chromosomes and researchers can look at gradual genetic mutations in them to “count” generations.
Other studies have used mitochondrial DNA, which women seem to pass down virtually unchanged from mother to daughter, to show that the genetic “Eve” lived 143,000 years ago.
The latest study, published in the November issue of the journal Nature Genetics, reconciles the two findings, and in the process the researchers came up with new tool for looking at how people are different from one another genetically.
They also added a great deal of detail to the family tree of all men living today, information that can be used by historians, anthropologists and other researchers. “We can look at the tree and see, ‘Oh, this section of the tree is where Asians go.’ We can say, ‘Oh, here is a Japanese Y chromosome and this is a Chinese Y chromosome,’” Underhill said.
Race Not Evident in Genetics
What the tree does not do, he stresses, is identify so-called races. Geneticists have long agreed there is no genetic basis to race — only to ethnic and geographic groups.
“People look at a very conspicuous trait like skin color and they say, ‘Well, this person’s so different’ ... but that’s only skin deep,” Underhill said. “When you look at the level of the Y chromosome you find that, gee, there is very little difference between them. And skin color differences are strictly a consequence of climate.”
But the differences, while tiny, are enough for experts such as Underhill’s team to try to figure out how many generations you have to go back to find a single man who is related to all living people today. “The history of our species is something on the order of 4,000 or 5,000 generations,” Underhill said.
Women were good at passing on their genes, while some men were less lucky. Underhill’s team found evidence of genetic bottlenecks that shortened the male genetic legacy.
What could explain them? Real-life scenarios from recorded history provide plenty of explanations.
Dominant Tribe Wins Women
“One tribe conquers another tribe. The dominant tribe, the successful tribe, gets to mate with all the women — its own women plus the women they conquered,” Underhill said.
Polygamy, a common practice, would also explain it. A few dominant males get to marry and have children and the rest see their genes consigned to the rubbish heap of posterity.