about two gardens.

So imagine one garden and it has

the perfect amount of sunlight,

and then you plant different flowers in that garden.

And you can look and say,

"Well, the differences between them

in these plants' heights is about the seeds that I planted.

They all have the perfect environmental conditions.

The differences between them are genetic."

Now imagine another garden, and it is neglected.

If you looked at that and you said,

"All those plants are stunted and dead,"

and then you said,

"Ah, the difference between these two gardens

is that these plants in the neglected garden

are genetically shorter than these plants

in the rich, well-resourced garden."

We can't then say that all the differences

between tall and short plants

across very different environments

are in fact due to genetics.

That's a really obvious thing when it comes to plants,

but it's a really difficult thing for people

to keep in mind when we're talking about individual

versus group differences.

This relationship between

heritability and response to the environment

is a complicated one.

'Heritability' is the proportion of variation

in a population that's due

to genetic differences between people.

It's a confusing term because people misinterpret heritable

to mean 'genetically determined,

unmodifiable by the environment, or innate.'

And it doesn't mean any of those things.

But it's hard for us scientists to describe why.

The thing about factoring in environment in genetic studies

is that we already face

an enormous, statistical power problem.

Do you have enough people?

Do you have enough observations?

Do you have enough data to be able to reliably say

that what you're picking up on is real

and not just random chance?

Genetic studies that ignore the environment

and are just looking for the "main effects"

of genes are already requiring sample sizes

in excess of one million people.

So when you start to factor in

gene-by-environment interaction,

the power problem gets even bigger.

Statistics is hard, biology is hard.

A lot of times people haven't had exposure to this

since high school, if at all.

In the larger conversation,

we're trying to make sense of information about race.

We're trying to make sense of information about genes,

about education, about inequality.

I think it's really understandable

that people have a hard time thinking

about how all these things go together.

'Portability' is this idea that what we've discovered

in one sample or one group of people,

how much can we port that over to a new group of people,

and trust that things are gonna work in the same way?

So we see this all the time with our social science effects.

A minimum wage change in one state

doesn't have the same effect as a minimum wage change

in another state.

What I think people often miss

is that genetic causes can operate in the same way.

So, just because a gene influences the probability

of an outcome in this group of people,

to the extent that that's probabilistic

rather than deterministic,

to the extent that that genetic effect

is moderated by the environment,

we're not gonna be able to expect it to be portable

when we study a new group of people.

When I say that something's heritable,

I mean that within a group of people

that have experienced

roughly-equivalent environmental conditions,

genetic differences between them are related

to the phenotypic differences between them.

The genes of the seeds are related to the height

of the flowers.

But that doesn't allow us to make the leap

that differences between groups

that have experienced

really different environmental legacies are due to genetics.