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36
How many possible humans are there? (lemmy.world)
submitted 6 hours ago* (last edited 5 hours ago) by gedaliyah@lemmy.world to c/asklemmy@lemmy.world
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Looking only at genetic code, is it possible that there have ever been two genetically identical people who are not twins (or clones)? How many medically distinct human beings can their actually be?

I'm assuming that we're only talking about biologically modern human beings. So the genes that make us human cannot be eligible for variation.

If we don't include environmental factors and non-DNA genetic material, what is the actual number of genes that can vary from one person to another? Do we even understand the human genome well enough to make this kind of calculation?

I'm assuming from combinatorial math that it's more humans than can ever exist through the course of the entire universe. But what is the actual number? If those genes are varied at random, how many people will it take before they say a 50% chance that two of them are identical? For example, it only takes 23 people to have a 50% chance that at least two of them have the same birthday.

Edit: I found an interesting article about the complications with trying to calculate this number. The number seems to be on the order of 10^(tens or hundreds of thousands)

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[โ€“] yesman@lemmy.world 6 points 6 hours ago (1 children)

The number of possible combinations of genes is so large that the chance of a random duplication is vanishingly small. Even twins aren't exact copies because they'll have mutations unique to themselves.

[โ€“] gedaliyah@lemmy.world 1 points 5 hours ago

The question isn't whether it's large. The question is how large is it? Right now the human population doubles every 40 years and that rate seems to be increasing.

If humans somehow expanded in population and efficiently consumed all of the energy in the universe, then that means maybe somewhere on the order of 10^65 possible people (according to some very bad napkin math just for the sake of argument).

Are there that many unique combinations of human DNA, ignoring mutations which would change the species or have no impact on biology?