Genetic Adam and Eve could have been contemporaries, scientists say
New research published in Science shows that our most recent common female and male ancestors could have been alive at the same time.
Thousands of years ago, somewhere in Africa, lived a man who – probably – had no idea that he, among all the other men in his group, would go on to become humankind’s most recent common male ancestor. Scientists would call him “Adam.”Skip to next paragraph
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Now, a new paper published in the journal Science significantly narrows the time during which Adam could have lived – about 120,000 to 156,000 years ago – putting him in about the same time period as humankind’s most recent common female ancestor, often dubbed “Eve." The research revises previous findings that dated Adam within a much longer period.
And the findings also ease recent doubts that the Y chromosome can reliably trace ancient lineage, renewing confidence that tracing and dating lineage using mutations in the Y chromosome could be critical in answering some of the vexing questions about how and where the first humans originated.
“We’ve shown that we can do this kind of dating, and that the Y chromosome is a really powerful tool,” says Brenna Henn, a genetics researcher at SUNY Stony Brook. “Now that we can use the Y chromosome in this manner, we can go back and look into other big questions, like exactly where in Africa did humans originate?”
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“The ultimate goal is to understand when and where there was a modern human population,” she says.
Dr. Henn and colleagues analyzed the Y chromosome from 69 men from nine globally divergent regions, including Namibia, the Democratic Republic of Congo, Gabon, Algeria, Pakistan, Cambodia, Siberia, and Mexico. The Y chromosome, which in human males is one chromosome of the 23 pairs that form the genome, is a useful means through which to follow paternal lineage, as it is passed as an exact copy from father to son, whereas other chromosomes are shuffled and reshuffled in the making of a new person.
The mitochondrial genome, passed from a mother to both male and female children, is likewise used to plot maternal lineage. It has been used to date Eve.
Still, over hundreds of thousands of years, the Y chromosome is not always faithfully copied. Like mitochondrial DNA, it mutates, and those mutations can be used to trace lineage. Researchers identified about 11,000 mutations in the genetic sequences of the 69 men, after comparing their sequences to what is known as the reference genome. Those mutations were then plotted as a family tree, with the tip of each branch representing an individual’s unique mutation not shared with any of the other men.
Scientists have long suspected that those mutations occur at a regular rate, which would make it possible to then attach a date to those mutations. But since there is not yet a standard mutation rate in genomics, the team had to create their own.
To do so, they referred back to a known event: the migration of humans in North America 15,000 years ago. Mutations common to all modern Native Americans must have existed prior to the peopling of the New World, whereas variants among that population must have developed during the past 15,000 years.
That 15,000-years-ago marker was used to give the scientists a rate at which mutations occur, which was then applied to the Y chromosome tree. All the calculations were then redone with the 69 men’s mitochondrial DNA, to also trace their common female ancestor.