Why did Darwin study barnacles for eight years, even ignoring doctors as his health failed? Was it the subject's alienness and the lure of a new truth hidden in the commonplace, asks Rebecca Stott.
What is the nature of intellectual curiosity that keeps the scholar slumped under an Anglepoise lamp until dawn? At what point does a research project become an obsession? Is it something to do with the gravity of the question: what part of the brain controls the sex drive of a rat, for instance, or what does Langland mean by sin? What does it take to make the long-slaved-for answers matter?
The subject of Charles Darwin's most arduous and intensive research project was one of the most commonplace and seemingly uninteresting creatures in the world: the barnacle. He studied it for eight long years in its two biological manifestations: the white-coned creature that encrusts all shoreline surfaces in the temperate world from Scotland to Australia and its claw-like stalked cousin, which colonises any floating piece of driftwood, whale flank or ship's hull.
From 1846 to 1854, Darwin teased out minute body parts - mandibles or parts of an oesophagus, for instance - with tiny pins in order to mount them on microscope slides. The work gave him headaches and nightmares and almost broke his health, but, despite the advice of doctors, he did not stop. Soon his study in Down House had become something of a laboratory. Daily, the postman delivered packages of barnacle specimens and collections posted to him from around the world.
When Darwin's young son visited the house of a neighbour during these years, he looked around for a study. When he was told that his friend's father did not have one, he asked, wide-eyed and incredulous: "But where does he do his barnacles?" George Darwin's eminent father "did" barnacles.
So - George assumed - did all other fathers. Piles of labelled pill boxes like little white coffins rose from every surface in his father's study.
They contained specimens of every known living barnacle from around the world and scores of fossil barnacle valves.
From before he could walk, George had seen his father, on a small stool mounted on castors, sitting motionless, his eye pressed to a microscope on a dissecting table in the window, or spinning around to his writing table to scribble a few words in a notebook. When George painted in the schoolroom, it would often be on the back of a discarded page from the barnacle manuscripts, a page of crabbed, mauled and mangled sentences, evidence of his father's daily struggle to put barnacles into words, eight years of struggle and sickness. Why did it matter?
What George didn't know was that locked in a drawer in that fascinating barnacle-crusted study was an incendiary essay about species that his father was not yet prepared to publish. Darwin might have published a shorter version of On the Origin of Species by Natural Selection in 1844 but for a series of happenings that together made him hesitate and that drove him to the barnacle work: in 1844, a speculative evolutionary book, Vestiges of the Natural History of Creation , was published and panned by fellow naturalists; in 1845, his botanist friend Joseph Hooker pronounced that "no one has the right to examine the question of species who has not minutely described many". One reason why Darwin worked on barnacles, then, might have been that, as a man who had minutely observed a corner of the natural world, he would earn the right to approach the species question.
Certainly the preface to On the Origin of Species by Natural Selection seems to confirm this. Darwin wrote defensively: "After five years' work I allowed myself to speculate on the subject [of species], and drew up some short notes; these I enlarged in 1844 into a sketch of the conclusions, which then seemed to me probable: from that period to the present day I have steadily pursued the same object. I hope that I might be excused for entering on these personal details, as I give them to show that I have not been hasty in coming to a decision."
But these hypotheses - that Darwin used the barnacle project to postpone having to publish his controversial species theory or to give him the right to pronounce on the species question - seem inadequate as explanations of his tenacity and perseverance. Historians have been baffled by the barnacle years.
Even with a working knowledge of barnacle life cycles, reproductive modes and evolutionary history, it is hard to imagine that one barnacle might sustain the interest of a speculative man such as Darwin for so long. And it was one barnacle that started it all: an aberrant barnacle, too small to see with the naked eye, that he had picked up on the shores of southern Chile ten years earlier. He nicknamed it Mr Arthrobalanus. One barnacle and one question: how and for what reason had this minute aberrant come to be? Of course, like others, he had not meant to take so long in answering. He had even thought that he might be able to solve the problem in a month or so. But this one puzzling barnacle specimen led to another - as barnacles do - and soon he realised that to understand the aberrance of the tiny creature he brought back from Chile, he would have to map the entire sub-group.
And that's when, of course, Darwin became hooked: the barnacle anatomy, when magnified by increasingly powerful microscopes, was a terra incognita , awesome, endlessly various and philosophically challenging. No person had walked here before. Darwin may not have left his study often in those eight years, but what George saw when he passed the open study door was a travelling man, a speculator with ideas, taking risks, seeking patterns, mapping a remote corner of the natural world.
But more than anything, perhaps what kept Darwin working through pain and discomfort and philosophical struggle was fascination with the strangeness of the subject itself, that nebulous quality that keeps us all in pursuit of a new truth however minute in scale; the fact that the seemingly commonplace so often takes on a new imaginative fascination when it comes to fill one's whole vision. What Darwin found in the depths of barnacle bodies was variation beyond his wildest imaginings, reproductive modes that took his breath away, the development of complemental males, living parasitically on the female, no more than reproductive sacs of sperm, with no heads, stomachs, digestive systems, but with the largest penises proportionate to size in the animal kingdom. It was a brave new world. Here was evidence of his theory too - barnacles had survived almost unchanged for thousands of years because they had adapted to their environments, they had shapeshifted every which way, come to reproduce every which way.
What Darwin saw on the stage of his microscope was more fabulous than he could have imagined: an evolutionary narrative branching out before his eyes as fascinating as the entangled family trees of the characters in a novel by Charles Dickens or Jane Austen. On the Beagle voyage, Darwin had worried that his species theory would make him a "Baron Munchausen of naturalists", but in the 1850s he found that nature told the tallest of stories all by herself.
Beyond Down House, these stories were opening up on the stages of other increasingly powerful and affordable microscopes, new romances that would capture the imaginations of writers and artists as well as scientists.
Charles Kingsley, who would write The Water Ba bies in 1863, was also glued to his microscope in these years in the 1850s. He wrote: "Without our improved microscopes, and while the sciences of comparative anatomy and chemistry were yet infantile, it was difficult to believe what was the truth; and for this simple reason that, as usual, the truth, when discovered, turned out to be far more startling and prodigious than the dreams that men had submitted for it, more strange than Ovid's old story that the coral was soft under the sea." Stranger indeed than fiction.
Strange enough to keep Darwin hooked.
Rebecca Stott is head of English and reader in Victorian literature and history at Anglia Polytechnic University. Her book Darwin and the Barnacle is published next week by Faber and Faber (£12.99).