David Reich

So that's like, what is it?

It's like 240 billion new point mutations every generation.

There's only 3 billion DNA bases in the genome.

So every mutation that can occur does occur about 100 times every generation.

And we're not mutation limited anymore.

And so it's not like you have to, that the mutations can arise again.

They do arise again.

But when the population is only 10,000, you have to wait dozens or hundreds of generations sometimes for the new mutation to occur.

I think that's not likely to be true, but it's an extremely interesting thing to think about.

So I think already when population sizes are on the order of a million or so, every mutation that can occur does occur within a few generations.

And so that's well before the Bronze Age, if you take the population even of a place like Europe.

But

also of other places, or maybe it's at the dawn of the Bronze Age or the farming period.

The question you ask is, maybe when the population is small, natural selection doesn't work effectively.

A common thing that people think about with natural selection, and that is true, is that in small populations, selection doesn't work effectively.

That's

because mutations bop around in frequency from generation to generation a lot in a small population just randomly.

So if you have a population of size 1,000, mutations will bop around by a frequency of 1 over 1,000 every generation.

And if the selection coefficient is less than that, it will be drowned in the random bopping around of frequencies due to genetic drift.

But that is already, for a population of 1,000, 0.1% selection coefficient is very weak.