History is often made through inadvertence—or at least not quite in the linear way historians imply when they recreate that history in their narratives. The stuff of history in real time is sometimes less grand than it seems in our historical reflections—or at least, than was appreciated at the time. On the day of the occasion of Darwin’s joint bicentenary with Abraham Lincoln, I found myself reflecting not so much on Darwin’s contribution to the theory of evolution, as to his crowning work, the project on which he labored for half his lifetime. I refer to his earnest study of earthworm poop.

Charles Darwin’s great voyage of discovery was—it is generally thought—to have been to the Galapagos Islands. Actually, the ones that occupied most of his time and attention were to the garden in his backyard. While Darwin made one trip to the Galapagos, in a voyage lasting five years, he spent more than 40 years on a single experimental project in his own English garden at Down House in Kent. This project involved an examination of earthworm poop, to try and figure out just what role earthworms played in the ecology of the soil.

Over a period of decades, Darwin observed the earthworms in his garden; studying their physiology; their behavior; and, especially, their role in fertilizing the soil. Many a night Darwin would take one or more of his children out into the garden to hold a lantern whilst he probed in the soil to uncover the nocturnal activities of the resident Down House worms. He strewn cinders from the family hearth in a patch over the garden ground and waited, decades, while the earthworms buried the cinders in coat after coat of earthworm dung. Periodically, Darwin and the children would venture out with shovel in hand to dig small trenches to record the depth of the sinking cinders. This went on for over forty years. One might fairly say, Darwin was obsessed with this topic. Here is how he described the great work, in his last book, published just six months before his death:

As I was led to keep in my study during many months worms in pots filled with earth, I became interested in them, and wished to learn how far they acted consciously, and how much mental power they displayed. . . . In the year 1837, a short paper was read by me before the Geological Society of London . . . in which it was shown that . . . [a] large quantity of fine earth continually [is] brought up to the surface by worms in the form of castings. These castings are sooner or later spread out and cover up any object left on the surface. I was thus led to conclude that all the vegetable mould over the whole country has passed many times through, and will again pass many times through, the intestinal canals of worms.

This rather earthy observation was the start of Darwin’s experiments with earthworms and their impact on the ecology of the soil. Darwin also invested considerable time and effort in studying the mentality of worms, to see if, for example, they were sensible to music (no, according to Darwin). Darwin was so impressed by the ceaseless labors of his segmented neighbors that he would be moved to conclude: “It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures.”

Among Darwin’s more than twenty published books (including his posthumously published autobiography), his 1856 On the Origin of Species was not his most successful. Several of Darwin’s books outsold Origin during Darwin’s lifetime, and his contributions to marine biology, botany, zoology and geology were all thought by his contemporaries to be of more significance than his work on evolution. Indeed, his book on his earthworm research appeared in October 1881 and was available for barely half-a-year before Darwin’s death. Even so, it outsold On the Origin of Species (which had been in print for more than 20 years) during Darwin’s lifetime. As far as Darwin knew, his study of earthworm poop seemed to have had a bigger impact on the world than his theory of evolution.

Such are the weird and wonderful ways of real history.

1 Darwin, Charles. The Formation of Vegetable Mould Through the Action of Worms, With Observations on Their Habits,(London, John Murray, Albermarle Street, printed by William Clowes and Sons, Limited, 1881): 2-4.

2 Ibid., 313.