I googled the amount of people that lived on earth throughout its entire history, it’s roughly 108 billions. If I take 1 person and multiply by 2 for each generation of ancestors, at the 37th generation it already outnumbers that 108 billions. (it’s 137 billions). If we take 20 years for 1 generation, it’s only 740 years by the 37th generation.
How??
(I suck at math, I recounted it like 20 times, got that 137 billions at 37th, 38th and 39th generation, so forgive me if it’s not actually at 37th, but it’s still no more than 800 years back in history)
In: 1391
There exists, in mathematics, something known as the “pigeonhole theorum” which simply states “if you have n available slots and more than n objects then by necessity there must be at least one slot which contains more than one object.”
In other words if I roll a 6 sided die 7 times, I have to have rolled at least one number at least twice.
So back to your question: for every generation back you go in your family tree (g) you have a number of ancestors 2^g at that generation level. So if 2^g is greater than the number of viable adults in the population than the pigeon hole theorun states that at least one person is at least two of your ancestors.
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