David Reich

There's probably very strong negatives to doing that.

You're probably sacrificing other things.

And I think that there's trade-offs probably, but I think it's highly likely that if natural selection was pushed any of these traits

in more in one direction than it is, the mean would move.

That's a rich question.

And I think that the human population has within it for complex traits, a tremendous amount of variation.

So within the human population, there's a huge amount of variation that affects height.

There's a huge amount of variation that affects

body mass index, if you take all these mutations and all set them to the high height variant, a person will be extremely tall, like as tall as a tall building, you know, if you, of course, which will never happen.

But if you take all these variants that affect schizophrenia risk, they will, and you point them all in the same direction, there will be extreme risk or extreme protection for schizophrenia.

So for complex traits, ones underpinned by many mutations,

All the variation already exists to move the population to a different adaptive set point that's optimal in the environment which it's in.

So if you push the population into a new environment within hundreds or thousands of years, the population can rapidly move to a new adaptive set point.

There are some unusual traits like ability to digest cow's milk or protection against sickle cell anemia that require a single very important mutation that may not yet exist in the population.

And then you have to wait for the mutation to occur in some people.

And when the populations are relatively small, only 10,000 people, you might have to wait dozens or hundreds of generations for that mutation to arise.

But when the populations are large, there's not mutation limiting anymore.

Every mutation that can occur does occur.

There's 8 billion people in the world.

There are maybe 30 new mutations every generation.