David Reich

And we hoped that as the numbers of samples would increase and we would get higher resolution to be able to appreciate differences in frequencies over time, we hoped that this would make it possible to detect far more.

And what was quite disappointing over the subsequent decade is that that didn't happen.

So, for example, the largest study of that type in 2024 by a group in Copenhagen analyzed the data, much better data than we had in 2015, and found only 21 positions that were highly different in frequency across time.

And while that was exciting, it was almost twice as many as we had found in 2015.

In a lot of ways, it was disappointing because the sample size and data quality had gone up so much, and yet this is all that was found.

And so what that suggested is that we might be hitting an asymptote, and we might not be able to get beyond where we currently were, and that this approach to learning about biology, which was very promising in theory, might actually not produce a high yield.

But maybe, in fact, natural selection was quiescent.

And in fact, the reason we're seeing so few changes is that actually there's not been a lot of adaptive directional selection yet.

So that was the situation we found ourselves in until just a few years ago when we carried out this study in our research group led by Ali Akbar.

So what we did is we deployed a few innovations or change to try to improve our power to detect natural selection.

One of them is we just pumped a lot of data into the system.

And so we increased the amount of data by about 14 fold.

And the main thing that we do in this study is we report data in this study from about 10,000 individuals with new data.

So this is like a very big increase in the amount of data in the literature.

And the total data set size of ancient individuals distributed over the last 18,000 years is about 16,000 people.

So this is a large data set.

It's much larger than was previously possible.

And when you have more data,

you can estimate frequency changes with much more subtlety.

And the data comes from only one part of the world, which is Europe and the Middle East.