On January 1835, on a beach in the Chonos Archipelago, off the coast of Chile, Darwin picked up a conch shell interested in some unusual boreholes drilled into its surface. So began Darwin’s study of barnacles. Back on board the Beagle he focused his microscope on the inhabitant of one of the holes. He was convinced it looked like a barnacle, but all his books told him all barnacles built themselves a house; this one was different. Intrigued, he decided to return to it later.
He did just that, but not for 11 years. In 1846, settled into a new house in Downe, Kent, and with a growing family, the barnacles were back in his thoughts. They had reason to be. Marine invertebrates were the darlings of British science in the mid 1800s; scientists were convinced they held secrets of life. Most of the great Victorian naturalists were busying away on some marine creature. The barnacles were one of the most mysterious and least studied groups. Until recently they had been classed as molluscs, but in 1832 William Vaughan Thompson had shown that the shelled, sessile adults developed from free swimming larvae; they were in fact Crustaceans (like crabs and lobsters). The young would swim around then, reaching adulthood, seek out a sturdy surface to spend the rest of its days. It would glue its head down to the rock, secrete a hard shell, and stick its feet out into the water sifting out even smaller creatures for food. But not much else was known about them.
In an article called The Present State of Zoology Darwin’s old friend Leonard Jenyns had put out a scientific call to arms, a thorough study of barnacles would yield important new discoveries and was overdue. Darwin was well primed for this call. In Edinburgh, mentored by Robert Grant he had begun his career working on sponges and on the Beagle voyage over half of his Zoology notebooks were devoted to marine invertebrates.
Barnacles offered Darwin an opportunity; if he could solve their mysteries and bring order to their messy classification he could make a large contribution to Zoology and cement his reputation as a leading naturalist. Besides, he already had a rare and intriguing collection of odd barnacles. How hard could it be? He reasoned he could wrap things up with the Cirrepedes in a year or so. One year was a bit optimistic, it would take eight.