Carl Zimmer

We understand why some people score higher on intelligence tests than others.

Not only that, but we think that people who score low on these tests should be sterilized.

There were thousands upon thousands of people who were sterilized in the United States based on a very wrong notion about heredity.

And Nazi Germany borrowed a lot of these ideas from the United States and took them to even more horrific extremes.

So whether we really understand heredity yet or not, it still matters enormously to us.

And so we have to really understand what do we really know about heredity so far and how much of this is just almost like illusions that we're giving ourselves about it.

Well, it's not random.

And you can actually put a number on that sometimes.

Scientists will call it heritability.

And so you can say, well, for height, how much of the variation in a population is due to the variation in their genes?

And the answer to that is about maybe 80%.

So really, genes play a huge role in whether people are tall or short.

So you get a lot from your parents in that regard.

There are other traits that are much less heritable, but there's still some heritability in them, like your personality.

Are you kind of a neurotic person, for example?

You get some of that genetically from your parents, but there's a lot of it is just

environmental variation.

And so it's not that heredity is meaningless.

It's just that it's really complicated.

And it's really interesting, too, especially because now we can look at individual genes.