Well today, Joe, you're going to tell us about work Darwin did, not on evolution - do I have this right? It's on earthworms?

JOE PALCA: Well exactly. I mean, it turns out that Darwin had a life-long interest in earthworms. And his book on earthworms called "The Formation of Vegetable Mould Through the Action of Worms," published in 1881, sold even better than "The Origin of Species" did during Darwin's lifetime.

Now, Darwin began his observations on earthworms as a young man and abandoned them to, you know, revolutionize biology. But it was late in life that came back to them. And he did his research at home in Kent, where I visited one cold and rainy afternoon last month. And the house is on a country lane, about 3.5 miles from the Orpington Train Station, and I produced a little piece about my visit. So let's listen.

BLOCK: Okay.

PALCA: There's a gate at the back of the house that leads down to a lawn.

Mr. ALUN ANDERSON (Journalist): At the time that Darwin started looking at the worms, no one appreciated the role they had in agriculture at all.

PALCA: That's Alun Anderson. He's actually a pal of mine, a fellow journalist. When I called him to say I was coming to England to do some stories about Darwin, he said oh, you've got to tell people about the earthworms. So he agreed to meet me at Down House - that's the name of Darwin's country estate -and talk worms.

(Soundbite of footsteps)

PALCA: As we squished our way across the lawn and toward a row of trees at the back of the property, Alun explained that in Darwin's time, most people thought earthworms were just a pest. But Darwin was convinced they were valuable for turning over the soil - in part, by chewing it up and pooping it out - and thereby making it more fertile.

To find out how fast the worms were turning the soil, Darwin did experiments. He started with something called clinker ash - small coal stones that are left behind in a coal fireplace.

Mr. ANDERSON: They're about the size of peas, white on the outside from the ash and black inside.

PALCA: Darwin would spread these stones across a field behind his house.

Mr. ANDERSON: And then he left them for 20 or 30 years. And then dug a trench across the land.

PALCA: And he looked in the walls of the trench to see how far down the stones had sunk through the action of the worms.

Mr. ANDERSON: And that was a complete surprise. No one had ever thought to think of the benefits of earthworms to the soil.

PALCA: As we wander down a path alongside one of Darwin's experimental fields, Alun says in his earthworm book, Darwin describes how his children helped with his work.

Mr. ANDERSON: Throughout the book, he keeps mentioning: Francis came out with me to hold the lantern - the candle lantern - while I looked at the worms in the dark. His other son played the bassoon to the worm to try to find out if the worm could hear sound or not. And he, obviously, was a great father, constantly involving his kids in his little experiments.

PALCA: Aw, dad?

Mr. ANDERSON: Dad, do we have to look at those worms again?

(Soundbite of laughter)

PALCA: So okay, it's true. Darwin's earthworm work probably isn't as important as his work on natural selection, but it does give you an insight into his genius.

Mr. ANDERSON: Only Darwin would go out there and start then to do experiments, and start to come up with a whole theory of what earthworms did and why they were beneficial. Everyone else just, sort of, took it as part of life and didn't think hard like he did.

BLOCK: Joe, I still want to know if the worms heard the bassoon.

PALCA: Apparently not.

BLOCK: After all that.

(Soundbite of laughter)

BLOCK: Well, that was a little experiment that failed. Tell us, Joe, how did your friend, Alun Anderson, start getting interested in Darwin's work on earthworms?

PALCA: Well, that's a pretty good story, too, as Alun told me. Here's what he said.

Mr. ANDERSON: Well, it all started, I had a telephone call from a Japanese professor - an old friend of mine who's very eccentric.

PALCA: The professor wanted to come to Down House and wanted Alun to contact the people in charge of the house, to see if he could see some of the experiments Darwin did there.

Mr. ANDERSON: And I said well, I can try asking if we could look at them. And he said, but to look at them properly, I'm going to have to dig up Darwin's garden. At that point, I said, what is this all about?

PALCA: The professor wanted to see if he could find some of those coal stones Darwin had put on the fields. Alun was dubious, but the people at Down House were willing to let them look. So his Japanese friend came to London.

Mr. ANDERSON: We went to a garden center nearby and bought a couple of shovels, and we came here. And we expected there would be, sort of, two guards and a tiny area we were allowed to dig. And they just said oh, that's the garden, you know, replace any turf that you dig up.

PALCA: They quickly found that the topsoil was only a few feet deep, and then they hit a layer of hard chalk.

Mr. ANDERSON: Eventually, after we tried a few different places in this lawn, we found a spot where, on the bottom-most layer of chalk, there was this sudden layer of small, nodular black granules of - that were clearly from coal. So we took a sample out. And we at least held it in our hands, and we thought, Charles Darwin was the last person to touch this, and we're the next. We were pretty thrilled to see it.

PALCA: So it's a kind of an interesting bit of Darwin memorabilia that he was able to dig up.

BLOCK: And Joe, you resisted the temptation to dig down for the coal stones yourself? You did not hold them in your hand?

PALCA: I'm afraid the day we were there, it was raining and freezing. And we ran out and did this interview, and we ran back inside.

BLOCK: You'll have to go back. Joe, thanks so much.

PALCA: You're welcome.

BLOCK: NPR's Joe Palca.

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