David Reich

And so maybe if the selection was 2% a generation, you would still only see maybe a 10% compounded effect.

And there's just not enough time to detect it.

But the Bronze Age is not 300 years.

It's 3,000 years.

It's the power of compound interest.

And you have enough time to begin to see a strong effect.

But this really, really, really does seem to be a very impactful time in terms of human history.

And you can see it in our complex traits.

So, for example, if you look at pigmentation, for example, which is the strongest signal of selection for a complex trait in humans.

our data set.

So you look at genetic mutations that are known to affect pigmentations.

You add up their effect across all of the DNA.

So there's dozens or hundreds of them.

And you look to see in what time is the natural selection strongest.

And the time period is really 2000 to 4000 years ago.

And for some of these other traits as well, you see, again, the time period over which the selection is strongest is 2,000, 4,000 years ago.

So, for example, if you look at genetic variants that affect measures of cognitive performance, for example—

such as performance on intelligence tests in people, in white British people today.

So this is, of course, a very strange trait to measure in the past because there were no intelligence tests and there was no school.

But it is a predictor today, and you could look at how it's changed in the past.