DNA demonstrates how closely everyone on Earth is related

By | January 3, 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.” …


3 thoughts on “DNA demonstrates how closely everyone on Earth is related

  1. Shirley Ravn

    That’s some twisted math. Have I lost a hundred IQ points since I woke up today or is this a joke? If there is anything about this that actually makes sense to you, please let me in on the logic as I haven’t been baffled in years. Seriously, if 10 generations ago each individual had a thousand ancestors and the number of ancestors doubles with each new generation, then the newest generation would have a million ancestors, not the people 20 generations ago. They would have had only 2 ancestors. Doubling with each new generation means the number of ancestors increases with each new generation, not with each previous generation. How does it make sense to say that my great great grandparents had more ancestors than my children do? It doesn’t. Please explain.

    1. Xeno Post author

      I see where you got confused. What he is saying is that you have 1,000 ancestors from 10 generations ago and YOU have more ancestors than that if you go back 20 generations, etc.

      Your family tree gets wider as you go back in time. If ANY of those pairs of your ancestors failed to reproduce, you would not exist. If you keep going down the tree at some point there are logically more ancestors below you at any one time period than there were individuals alive on the planet at that time, therefore, we are all inbred mutants. Follow? A million logical ancestors can be fewer actual individual ancestors.

      If your mother and father were third cousins (see this http://en.wikipedia.org/wiki/Cousin) then five generations back you still have 18 logical ancestors, but you only have 16 actual ancestors because your great great grandmother on your father’s side (Betty) has the same parents as your great great grandfather on your mother’s side (Charles).

      Quiz: If your mother and father were fourth cousins then six generations back you have how many logical and how many actual ancestors?

      No one is saying that one of your ancestors 10 generations ago had more ancestors than you do now! That is clearly impossible … unless one of your other ancestors unrelated to that ancestor of 10 generations ago was created by fewer than two patents…

      The calculations that prove we are all related assumes two and only two parents for every human who ever lived. Based on that assumption, every human at any point in history had 1,000 relatives 10 generations before.

      Imagine a time in our history when you had a world human population of 10,000 ten generations ago and there are also 10,000 people alive today, each of which has 1,000 ancestors. You can visualize that everyone is related more easily that way. There were not enough people alive 10 generations ago for each person alive now to have had a different 1,000 ancestors in that scenario.

      Even more, even if every one of those 10,000 from 10 generations ago had children, some lines don’t continue when some in that line of ten generations do not reproduce. Thus, the 10,000 alive in our model are the result of only the successful lines from 10 generations ago, the ones that were the most genetically fit and/or lucky.

      Human parthenogenesis (E.g. a child from just a chimera mother who has both sperm and eggs) is not 100% impossible, but is rare enough to discount. The creation of a functional human from scratch with zero parents (for example, by aliens) is even less likely as far as we know. Both of those would increase the possibility that there is someone alive today to whom you are unrelated.

      Actually, we are likely even a bit *more* related than this model’s assumptions because there were probably (but very rarely) in our history times when one human female egg was fertilized by two different men at the same time and the resulting person had three biological parents instead of two. Roman orgies, etc. Two sperm can fertilize a single egg, and twins can even have different fathers, but this happens rarely.

      1. Shirley Ravn

        Xeno, it took me two years to see this, but thank you so much and I do get it now. It’s been so long since I’ve been here that I forgot how much I like your page. I’ll be back soon to catch up. Much respect.


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