In the spring of 1876, a young man of nineteen arrived in the seaside city of Trieste and set about a curious task. Every morning, as the fishermen brought in their catch, he went to meet them at the port, where he bought eels by the dozens and then the hundreds. He carried them home, to a dissection table in a corner of his room, and—from eight until noon, when he broke for lunch, and then again from one until six, when he quit for the day and went to ogle the women of Trieste on the street—he diligently slashed away, in search of gonads.
“My hands are stained by the white and red blood of the sea creatures,” he wrote to a friend. “All I see when I close my eyes is the shimmering dead tissue, which haunts my dreams, and all I can think about are the big questions, the ones that go hand in hand with testicles and ovaries—the universal, pivotal questions.”
The young man, whose name was Sigmund Freud, eventually followed his evolving questions in other directions. But in Trieste, elbow-deep in slime, he hoped to be the first person to find what men of science had been seeking for thousands of years: the testicles of an eel. To see them would be to begin to solve a profound mystery, one that had stumped Aristotle and countless successors throughout the history of natural science: Where do eels come from?
The nineteenth century had brought Darwin and Mendel, Pasteur and Mendeleev, and a growing sense that scientists (a word coined only in the eighteen-thirties), with their studies and their systems and their microscopes, were at last equal to solving the great quandaries of the natural world. Questions that had befuddled mankind for centuries—where life comes from, what it is made of, how it changes, why it ends—were now seen as knowable, quantifiable, explicable. Just two years before Freud arrived in Trieste, the German biologist Max Schultze, lying on his deathbed, observed, perhaps wistfully, that he was leaving a world where “all the important questions . . . had now been settled.” All of them, that is, “except the eel question.”
What could be more ordinary than an eel? Not so long ago, European eels, Anguilla anguilla, were widely eaten. In Sweden, they might be smoked, braised in beer, or fried in butter; in Italy, boiled in tomato sauce; in England, jellied in stock, or fried with eggs into an elver cake. They were a simple and abundant food enjoyed by members of the poorer classes, like the Cockney woman described in “King Lear” who accidentally puts them in a pie still alive.
People caught eels in brooks, rivers, lakes, the sea. They also caught them, inexplicably, in ponds that dried out and refilled each year, and that had no access to other bodies of water. They couldn’t help but notice that the creatures seemed to have no ovaries, no testicles, no eggs, no milt. That they were never observed to mate. That they sometimes seemed to issue from the earth itself. Eels were unaccountable, and so, writes the Swedish journalist Patrik Svensson in “The Book of Eels” (Ecco), an unusual and beguiling guide to an unusual and beguiling animal, it fell to us to try our best to account for them.
The ancient Egyptians believed that eels were produced by the sun warming the Nile; Aristotle decided that eels emerged spontaneously from mud and rainwater. Pliny the Elder thought that new eels developed when old eels rubbed away parts of their bodies on rocks. As late as the eighteen-sixties, a Scottish author espoused an old belief that they began their lives as beetles. “Some believed eels were born of sea-foam,” Svensson writes, “or created when the rays of the sun fell on a certain kind of dew that covered lakeshores and riverbanks in the spring. In the English countryside, where eel fishing was popular, most people adhered to the theory that eels were born when hairs from horses’ tails fell into the water.”
The truth emerged only slowly, and was, in its own slippery way, stranger than the fiction. Careful observers discovered that what had long been taken for several different kinds of animals were in fact just one. The eel was a creature of metamorphosis, transforming itself over the course of its life into four distinct beings: a tiny gossamer larva with huge eyes, floating toward Europe in the open sea; a shimmering glass eel, known as an elver, a few inches in length with visible insides, making its way along coasts and up rivers; a yellow-brown eel, the kind you might catch in ponds, which can move across dry land, hibernate in mud until you’ve forgotten it was ever there, and live quietly for half a century in a single place; and, finally, the silver eel, a long, powerful muscle that ripples its way back to sea. When this last metamorphosis happens, the eel’s stomach dissolves—it will travel thousands of miles on its fat reserves alone—and its reproductive organs develop for the first time. In the eels of Europe, no one could find those organs because they did not yet exist.
But, even as these answers were arrived at, “the eel question,” as it was widely known, proved to be as changeable as the eel. It seemed to be forever unsolvable, for behind any eel answer there was always another eel question, shrouded by more layers of mystery.
“We know, then, that the old eels vanish from our ken into the sea, and that the sea sends us in return innumerable hosts of elvers,” a Danish searcher, Johannes Schmidt, wrote. “But whither have they wandered, these old eels, and whence have the elvers come?” Schmidt became consumed by his questions; in 1904, he left his family in Copenhagen and set out to scour the seas for the very smallest of eels. For seven years, he trawled the coasts of Europe, but found only larger larvae. For another three years, he enlisted shipping companies to net larvae as they plied the North Atlantic, and turned his own schooner west and south. Net by net, he mapped the ocean according to which parts of it contained eel larvae, and how large those larvae were, until the tiniest ones led him to their point of origin. It was a slow process, made slower by a shipwreck and a world war. Finally, nineteen years after he first set out, Schmidt announced his findings. “How long the journey lasts we cannot say,” he wrote, summoning the grandeur warranted by the occasion. “But we know now the destination sought: a certain area situated in the western Atlantic, N.E. and N. of the West Indies. Here lie the breeding grounds of the eel.”
Schmidt had traced the Anguilla anguilla to the Sargasso Sea—a sea within a sea, a garden of seaweed bounded not by land but by great currents of water. (The American eel breeds there as well, and it is still something of a mystery how the larvae, all mixed together but genetically distinct, know which continent is their future home. The Japanese eel has its own breeding grounds, in the Pacific, and another famous freshwater eel, the electric one of South America, is not actually an eel at all; it’s a knifefish.) Schmidt’s discovery was an answer, and, in the past century, no one has successfully challenged it; that European eels come from the Sargasso Sea remains the official word of science. But, as with that sea and the animal born there, the boundaries of this knowledge are fluid and strange. Many expeditions have followed Schmidt to the breeding grounds in the decades since, each with better technology than the last. They, too, have found plenty of larvae, but, when one expedition collected and examined seven thousand fish eggs, not one of them turned out to be from an eel. Scientists have put G.P.S. trackers on silver eels beginning their migration; they’ve used hormones to bring females into heat, transported them to the breeding grounds, and attached them to buoys to use their pheromones as bait. They have dropped microphones into the water and opened the stomachs of predators. And yet no one has ever seen Anguilla anguilla mating anywhere, or so much as set eyes on a mature eel, living or dead, in the Sargasso Sea.
When Svensson was a child, in Sweden, he spent many evenings with his father, a road paver, on the banks of a stream that ran past his father’s childhood home. Together, as dusk fell, they would rig and bait their lines and throw them into the stream, then drive home to the swooping of bats. At sunrise, they checked to see which hooks had been taken by yellow-brown eels, which they collected in buckets and ate fried or boiled. (His father relished the taste, but Svensson found it nauseating; it was the fishing, and the time with his father, that he loved.) He describes his father as a thoughtful man, “fascinated by all the strange and wonderful forms life took,” but most of all by the peculiarity of eels: “ ‘They’re odd, eels,’ Dad would say. And he always seemed mildly delighted when he said it. As though he needed the mystery. As though it filled some kind of emptiness in him.”