David Reich

We're talking about 1% effects, and that's very strong.

It will work very well even in a population of a size of 1,000 or 10,000.

If you are talking about mutations of the type that will start rising only in large populations but not small populations—

Those are selection coefficients that are on the scale of 1 over 10,000 or 1 over 100,000.

And those ones will take 10,000 or 100,000 generations to rise in frequency, which is hundreds of thousands or millions of years.

So that's not going to do anything over the timescale we're talking about.

There's just a timescale issue.

I understand.

We're talking about strong measurable selection coefficients on the order of half a percent or more in this study.

And all of those are going to work in small populations or large populations.

It's not going to be affected by the population size.

It's very interesting.

And it's actually not widely understood.

Yeah.

Right.

50,000 years ago or so, or maybe 100,000 to 50,000 years ago, there's a quickening of the pace of change in culture.

You see the first extensive representational art and bead necklaces and drawings on the wall and so on and so forth, and also a rapid increasing pace of innovation, the types of tools that people use.

And so the thought might be that there was going to have been some kind of genetic switch, a kind of important genetic change that occurred in the population and that swept to high frequency, and that everybody suddenly had, soon had, and that made it possible to do these things, maybe some genes that allowed people to have complex language, representational language, for example.

And so one thing that we did in 2016 in this paper by Shatmalik and colleagues is we looked across the DNA for places that might be expected to look like this, that where all people living today or nearly all people living today share a common ancestor, maybe 100,000 or 200,000 years ago.

And we looked really hard and right across all the DNA we could look at, we couldn't find anything more than four or 500, more recent than four or 500,000 years ago.