Carl Zimmer

It's been traveling down our species probably for hundreds of thousands of years, and it's a real secret to our success as a species.

Well, one reason the book is so thick is because heredity has this long, deep, powerful history.

Heredity means a lot to us.

And so part of what I'm doing in the book is trying to explore why it means so much to us, and also what kind of trouble we can get ourselves into by searching for that value.

There's some very dangerous aspects to our obsession with heredity.

You can look to the early 1900s in the United States.

When genetics emerged, there were a number of very powerful voices who said, aha, we understand heredity completely.

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.