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September 3rd, 2009

jarandhel: (Default)
Thursday, September 3rd, 2009 10:48 am
We're all mutants, say scientists.

How many of your ancestors are you related to?

It is believed that the human genome is roughly 3 billion base pairs long. Contained within these base pairs are approximately 25,000 distinct genes.

After 15 generations, not taking into account your individual or inherited mutations, you would have 32,768 ancestors. You would have inherited zero genes from 7,768 of them.

After 32 generations, again not taking the mutation rate into account, you would have 4,294,967,296 ancestors. Mathematically, more than a billion of them could not have contributed so much as a single base pair to your genetic makeup.

As a corollary to this, it should be noted that there have been approximately 22 generations in America since 1492.  This gives us an average of 1 generation every 23.5 years.  Using that figure, it has been roughly 50 generations since the death of Charlemagne.  You have one quadrillion ancestors from a generation that far back.  So even if, like me, you are related to him there is roughly one chance in 333,333 that you inherited so much as a single base pair from him.  That's less than half the chance of winning the lottery.

The idea that you may have inherited a complex trait from him? (not share, inherited)  Pretty laughable.  Especially after taking the mutation rate into account.

Food for thought.
jarandhel: (Default)
Thursday, September 3rd, 2009 03:22 pm
Identical Ancestors Point

Apparently there is a point, when you trace genealogies far enough back in time, where you can break the humans who were alive then down into two groups: those who have left no genetic descendants, and those who are genetically related to all currently-living modern humans.

This point is estimated to be between 15,000 and 5,000 years ago.  This gives us a range of somewhere between the domestication of the Dog and the Bronze Age.

So, unless a hypothetical ancestor (supernatural or otherwise) is more recent than that time period, it's just as likely that (if they left any descendants at all) everyone on earth is descended from them.

Not, as I've already shown, that this means they would have necessarily inherited any DNA from them.  The chances of even inheriting one base pair from someone that far back is roughly 1 in 2.194 septendecillionNo, I didn't make that word up.