DNA demonstrates how closely everyone on Earth is related

Posted on 3 Jan 2014


Just from some basic math you can see that everyone alive today is related.


New research by Peter Ralph of USC Dornsife has confirmed that everyone on Earth is related to everyone else on the planet. …

The assistant professor of ‘s background in math and statistics enables him to develop methods and models and perform data analysis on , which he applies to learn about evolution and .

His latest research, which he conducted with Graham Coop, a at University of California, Davis—his former postdoctoral advisor—provided DNA-based evidence to confirm the that everyone on Earth is related.

“The fact that everyone has two parents means that the number of ancestors for each individual doubles every generation,” Ralph said. “By using basic mathematics, we can calculate that ten generations ago each individual had a thousand ancestors, and 20 generations ago they had a million and so on.

“But when we get to 40 generations ago, in the time of Charlemagne, we arrive at a trillion ancestors and that is a problem because we now have more ancestors than there were people. Thus one can deduce that a lot of those ancestors must be the same person.”

To visualize this concept, Ralph suggests drawing an imaginary family tree.

“At first it does look like a tree, with the branches doubling every generation, but then pretty soon the branches start running into one another and it begins to resemble more of a web-like tapestry as distant cousins marry and share a set of distant grandparents,” he said. “That means that although hardly anyone marries their cousin in Western Europe, many people are unwittingly marrying their 30th cousin.”

A paper published in 1999 by Joseph Chang, a at Yale University, analyzed this tapestry mathematically and concluded that we all share a . Indeed as we move back in time, the number of common ancestors of the living population increases until the point where “all individuals who have any descendants among the present-day individuals are actually ancestors of all present-day individuals.” …


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