Humans Are All More Closely Related Than We Commonly Think

The consequence of humanity being “incredibly inbred” is that we are all related much more closely than our intuition suggests, Rutherford says. Take, for instance, the last person from whom everyone on the planet today is descended. In 2004 mathematical modeling and computer simulations by a group of statisticians led by Douglas Rohde, then at the Massachusetts Institute of Technology, indicated that our most recent common ancestor probably lived no earlier than 1400 B.C. and possibly as recently as A.D. 55. In the time of Egypt’s Queen Nefertiti, someone from whom we are all descended was likely alive somewhere in the world.
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From the author is Scott Harrison’s bio:

“I recently earned my bachelor’s degree at Washington University in St. Louis with majors in Physics and Mathematics and a minor in Spanish.” (small world :slight_smile:

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Another great quote from the Scientific American quote:

" People are more closely related genealogically than genetically for a simple mathematical reason: a given gene is passed down to a child by only one parent, not both. In a simple statistical model, Manrubia and her colleagues showed that the average number of generations separating two random present-day individuals from a common genealogical ancestor depends on the logarithm of the relevant population’s size. For large populations, this number is much smaller than the population size itself because the number of possible genealogical connections between individuals doubles with each preceding generation. By contrast, the average number of generations separating two random present-day individuals from a common genetic ancestor is linearly proportional to the population size because each gene can be traced through only one line of a person’s family tree. Although Manrubia’s model unrealistically assumed the population size did not change with time, the results still apply in the real world, she says."

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On the Genealogy of a Population of Biparental

“If one goes backward in time, the number of ancestors of an individual doubles at each generation. This exponential growth very quickly exceeds the population size, when this size is finite. As a consequence, the ancestors of a given individual cannot be all different and most remote ancestors are repeated many times in any genealogical tree. The statistical properties of these repetitions in genealogical trees of individuals for a panmictic closed population of constant size N can be calculated. We show that the distribution of the repetitions of ancestors reaches a stationary shape after a small number G c ∝log N of generations in the past, that only about 80% of the ancestral population belongs to the tree (due to coalescence of branches), and that two trees for individuals in the same population become identical after G c generations have elapsed. Our analysis is easy to extend to the case of exponentially growing population.”

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Another article:

On the number of ancestors to a DNA sequence

If homologous sequences in a population are not subject to recombination, they can all be
traced back to one ancestral sequence. However, the rest of our genome is subject to
recombination and will be spread out on a series of individuals. The distribution of ancestral
material to an extant chromosome is here investigated by the coalescent with recombination,
and the results are discussed relative to humans. In an ancestral population of actual size
1.3 million a minority of< 6.4% will carry material ancestral to any present human. The

https://www.genetics.org/content/147/3/1459.short

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