Darwin's Earthworm Experiments Broke New Ground

Enlarge this image toggle caption Joe Palca/NPR Joe Palca/NPR

Digging In Darwin's Garden By doing experiments in his yard, Darwin proved that earthworms were turning the soil and making it more fertile. This was a surprising finding to 19th-century gardeners, who thought the worms were pests. Joe Palca speaks with science journalist Alun Anderson about why he dug up Darwin's garden.

Enlarge this image toggle caption Sir Arthur Keith/Nature Sir Arthur Keith/Nature

Many people know about Darwin's famous voyage aboard the Beagle — of his observations of the birds on the Galapagos Islands. Less well known is that Darwin spent quite a bit of time studying earthworms.

Initially, his earthworm work drew as much, or more, attention as his evolution work. His book, The Formation of Vegetable Mould Through the Action of Worms, With Observations on Their Habits, published in 1881, sold even better than On the Origin of Species during Darwin's lifetime.

Darwin began his observations on earthworms as a young man, but abandoned them to fiddle around with revolutionizing biology. It was only late in life that he returned to his worm pursuits.

He did most of research at Down House, his country estate outside London.

"At the time when Darwin started looking at the worms, no one appreciated the role they had in agriculture," says Alun Anderson, a journalist who became interested in Darwin's worm work.

In fact, Anderson says, in the mid 19th century, most people thought earthworms were pests.

But Darwin was convinced they were valuable for turning over the soil, in part by chewing it up and pooping it out, thereby making it more fertile.

To find out how fast the worms were turning the soil, Darwin did experiments. He spread small coal stones across a field behind his house and left them for 20 or 30 years. Then, he dug a trench across the land and looked in the walls of the trench to see how far down the stones had sunk through the action of the worms.

It's true that Darwin's earthworm work probably is not as important as his work on natural selection. But it does provide an insight into his genius.

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