The violence of the backlash shocked Darwin and sent him back into scientific hiding. He had not realized just how strongly Sedgwick and his other teachers were opposed to evolution. But he would not abandon his theory. Instead, he would figure out how to avoid Chambers’ fate.
Darwin could see that Vestiges had clear weaknesses. Chambers had simply read other people’s ideas and crushed them together into a shoddy argument. In some ways, Darwin was guilty of the same failing—his ideas were based on things he had read or heard from dozens of people—Lyell, Malthus, even his hairdresser. While he was recognized now as an authority on geology, he worried that he’d be treated as a dilettante when it came to biology. In order to be taken seriously, he had to show himself to be a first-class naturalist, able to wrestle with the complexities of nature.
He turned to the Beagle specimens he hadn’t yet examined in the eight years that he had been back. In one of his bottles there was a barnacle. Although most people think of barnacles as nothing more than something to scrape off boat hulls, they are actually some of the most unusual creatures of the ocean. Initially zoologists thought they were mollusks, like clams and oysters, with their hard shells cemented to a flat surface. In fact, barnacles are crustaceans, like lobsters and shrimp. It was only in 1830 that their true identity was discovered, when a British army surgeon looked at their larvae and found that they had a resemblance to young shrimp. Once barnacle larvae are released into seawater, they search for a place to land—whether it is a ship’s hull or a clamshell—and settle headfirst onto their chosen surface. They then lose most of their crustacean anatomy, developing instead a conical shell, out of which they extend feather-like feet that they use to filter food.
In 1835, off the coast of Chile, Darwin had collected a species of barnacle the size of a pinhead, latched to the inside of a conch shell. Looking at them under his microscope, he now realized that each barnacle was actually two—a large female with a minuscule male attached to it. At the time, scientists were most familiar with hermaphroditic forms of barnacles, equipped with both male and female reproductive organs. The pinhead barnacle was so strange that Darwin was sure it was a new genus.
Darwin was off on another long journey. At first he planned simply to write a short paper describing his discovery. But to do so, he had to figure out where among the many barnacle species he should classify it. He asked Owen to loan him some barnacles and to give him some advice on how to do the work properly.
Owen explained to Darwin that he needed to link his barnacle—no matter how strange it might be—to the basic crustacean archetype. By the 1840s, Owen had decided that archetypes were the key to zoology. Owen himself tried to reconstruct the vertebrate archetype, which he imagined was little more than a spinal column, ribs, and a mouth. This body plan didn’t exist in nature, Owen claimed; it was only a blueprint in the mind of God, on which He based more and more elaborate forms. You could see the connection to the archetype if you compared different vertebrates.
Take, for instance, a bat, a manatee, and a bird. The bat has a wing made of a membrane stretched over elongated fingers. A manatee has a paddle for swimming. A bird has a wing as well, but it consists of feathers pinned to hand bones that have been fused together into a hinged rod. Each of these vertebrates has limbs that are adapted to its way of life, but they also correspond to one another precisely, bone for bone. They all have digits connected to marble-like wrist bones, which are connected to two long bones that meet at the elbow with a single long bone. These correspondences (which scientists call homologies) revealed to Owen a common body plan.
Owen urged Darwin to look for homologies between barnacles and other crustaceans. Darwin privately thought that Owen’s archetype was nonsense. He thought that the similarities among vertebrates were a sign of their descent from a common ancestor. But to trace the evolution of barnacles from less peculiar crustaceans, Darwin would have to look at a lot of barnacles (1,200 species are known today). He borrowed collections from other naturalists, he studied fossil barnacles, and he even got hold of the British Museum’s entire stash. Darwin would end up spending eight years studying barnacles. All the while, his explanation of evolution, an idea as revolutionary as Copernicus’s sun-centered cosmology, sat sealed on a shelf.
Why the delay? Fear may have made Darwin procrastinate as he put off the inevitable confrontation with his mentors. Another reason may have been that Darwin was tired. He had taken a grueling five-year voyage, followed by eight fierce years of writing books and papers. His health had deteriorated after his return to England, to the point that he now was regularly devastated by bouts of vomiting. Darwin was in his mid-thirties and ready for some peace.
And yet another part of the delay was grief. His favorite daughter, Anne, died of the flu in 1851 at age 10. As he witnessed her undeserved agony, Darwin gave up on the angels. After Anne’s death, he couldn’t talk to Emma about his crumbling faith. Studying barnacles may have become a way to hide from the pain.
But fear, exhaustion, and grief aside, Darwin was enchanted by his barnacles. They turned out to be a perfect group of animals to study in order to learn how evolution worked. Darwin could see, for instance, how the ancestors of his Chilean barnacles could have descended from hermaphrodites, which had evolved through transitional forms until they began producing males and females. Darwin was also impressed by the variation that he found among the members of individual species of barnacles. No part of the barnacle anatomy was uniform. Here, Darwin realized, was a huge reservoir of raw material for natural selection to work on. Originally he had thought that a species would be subject to natural selection only at certain times—when islands emerged or continents began to sink, for instance. But with so much variation to choose from, natural selection could actually be at work all the time.
None of these thoughts made it explicitly into Darwin’s barnacle writings. He published a 1,000-page tome, for which he won praise, awards, and the respect he wanted as a naturalist. By 1854 he was ready to get back to thinking about natural selection.
Darwin began by addressing some doubts that Joseph Hooker had raised. One of Darwin’s claims was that the plants and animals living on islands had not been created there, that they were modified descendants of colonists. If that were true, then they needed a way to get to the islands in the first place. Hooker, a seasoned botanist, knew that seeds could travel for miles by wind or water, but he doubted that they could travel the enormous distances that Darwin claimed.
Darwin met Hooker’s doubts by throwing seeds into tanks of saltwater and found that they could be soaked for four months and still sprout when he planted them in dry ground. He discovered that birds could carry seeds on their feet, and that seeds could even survive being eaten by owls, passing out of their bodies with their droppings. Darwin’s theory had generated a hypothesis, and the hypothesis passed a test.
Darwin also went back to his studies of breeding. He drank gin with pigeon breeders as they explained to him how to use tiny variations to produce entirely new forms of birds. Darwin raised pigeons of his own, killing them and boiling the flesh off their skeletons so that he could measure the variability among them. He found that each breed was so distinct that if it were wild, it would be considered its own species. Almost every part of a pigeon’s anatomy was distinct from that of other varieties, from their nostrils to their ribs to the size and shape of their eggs. And as far as anyone could tell, every pigeon variety descended from a single kind of wild rock dove.