Darwin's Ghosts

by Rebecca Stott

  Palissy’s books disappeared from the shelves of Paris libraries, only to be rediscovered again 150 years later in another garden in the city, the mighty Jardin des Plantes, by the great naturalist the Comte de Buffon, who was looking for writings on fossils. Until then Palissy’s ideas about the origins of life had left no trace. When auditors arrived in Paris in 1589 to assess the famous Tuileries Gardens as part of the estate of the recently deceased Queen Mother, they found the grotto in serious disrepair and not worth inventorying, its clay animals broken and scattered about the grotto and the surrounding gardens. In the nineteenth century, excavators working in the foundations of the Louvre found fragments of clay animals, ostrich feathers, lion heads, fish, crabs, and salamanders buried deep in the soil of the palace gardens among ceramic human faces covered in shells and leaves turning slowly back into rock.

  *It was vandalized by Napoleonic soldiers in the early nineteenth century and narrowly escaped the bombs of the Allies in the summer of 1943.

  *There are several copies of Leonardo’s lost Battle of Anghiari: an anonymous copy in oils painted on a wooden panel is called the Tavola Doria; there is a painting by Lorenzo Zacchia dated 1558, and the Rubens watercolor, which is in the Louvre.

  *The Church’s powers of surveillance and inquisition became even stronger after the sequence of decrees and doctrinal definitions issued by the Council of Trent between 1545 and 1563.

  *Shallow pools covered with a clay or claylike residue.

  5

  Trembley’s Polyp

  THE HAGUE, 1740

  The Count of Bentinck’s summer residence* once stood in spectacular gardens on the edge of sand dunes that stretched down from the outskirts of The Hague to the North Sea at the port of Scheveningen. Within a series of elaborately patterned parterres, gardeners clipped trees and cone-shaped and tunneled hedges into carefully orchestrated symmetries. Exotic flowers bloomed in carved stone pots among classical statues. An artificial hill called Mount Parnassus rose against the skyline, netted with a symmetrical system of paths. Complicated latticework tunnels led from one part of the park to another through a system of ornamental ponds teeming with exotic fish. Everywhere in this garden, nature had been sculpted, ordered, restrained, symmetrized, and framed.

  In the summer of 1740, in a large study looking out over the orangery, the count’s two young sons—six-year-old Antoine and three-year-old Jean—and their thirty-year-old Genevan tutor, Abraham Trembley, peered into glass jars arranged along the window ledge. The count and countess were in the midst of an acrimonious divorce; the boys’ mother had returned to Germany, where she was already living openly with her lover, and, as their father spent much of his time with his lawyers in The Hague, this summer, the fascinating Monsieur Trembley had become the Bentinck boys’ entire world. The boys and their tutor were together night and day. Trembley taught the boys to read and write and to become fluent in French, Latin, and English; the young man worked hard to make everything they learned seem like play. He was passionate about teaching. He made sure the boys spent as much time outside as inside, catching aphids or caterpillars by day, moths in the evening, using the microscope, taking thermometric measures, speaking in French, declining Latin verbs. Trembley carefully prepared object lessons for them, using the study of a moth or a community of insects living on a single tree or the germination of seeds or the arrangements of a beehive as an opportunity to teach French, logic, morals, religion, history, science, and mathematics. “So far as is possible,” he wrote, “it is advisable that ideas should be preceded in the mind by curiosity—by the kind of curiosity that excites and sustains attention and thereby helps to cause objects to be seen in a precise manner and to be observed with pleasure.” To this end he had turned his study into a laboratory.

  Abraham Trembley and the Bentinck boys at work in Trembley’s study at Sorgvliet.

  Abraham Trembley, Memoires (1744)

  The boys had spent the morning wading through the ditches and ponds of the estate collecting water creatures and had returned to inspect their treasure. Under the magnifying glass and in the light of the sun, the water teemed with bright, moving green forms, some like flecks of grass, others resembling the tufts of dandelion seed heads. The boys, their fingers pressed up against the sides of the glass, called the flecks plants, but Trembley, raising his magnifying glass to the jars, was not so sure.* He shook the glass slightly; in the agitated water the creatures contracted to the size of a grain and then slowly extended their arms again. “I was surprised,” he recalled later, “and this surprise only served to excite my curiosity and redouble my attention.” The creatures in the jar moved by themselves and were sensitive to movement. These were characteristics of animals, not of plants, he reminded the boys.

  An early-nineteenth-century print of the polyp (hydra) showing its varied movements.

  Copper engraved antique print by J. LeKeux, published in Zoological Lectures, delivered at the Royal Institution, 1809

  A few days later the two excited boys called their tutor to show him the creatures walking like caterpillars across the inside of the jar. These strange creatures were about to make philosophical history; they were about to upset what eighteenth-century naturalists believed to be natural laws. And they were about to make Trembley’s name famous across Europe and, despite his resistance, embroil him in the spread of atheism.

  That summer, Trembley’s natural history interests lay with moths and aphids. Inspired by the French natural historian René Réaumur’s dazzling new volumes on insects, which he had read the previous summer, Trembley had begun to collect the caterpillars of carpet moths, sealing them in glass powder jars with pieces of woolen cloth to watch them pupate, hatch, and fly. In the book that had become Trembley’s bible, Réaumur had called on all natural philosophers to collect facts about insects. Facts—not speculations—were needed, he insisted, if nature’s laws were to be fully understood.

  Every week Trembley corresponded with his brilliant nephew, Charles Bonnet, who lived in Geneva. The young men were close. Both were pious Huguenot second-generation refugees who had grown up in the small Protestant republic of Geneva and attended the Academy there. Their families had fled France for Geneva either shortly before or just after the St. Bartholomew’s Day Massacre in 1572. Bonnet, though ten years younger than Trembley, was intellectually more precocious and philosophically inclined. His natural curiosity had already brought him to the notice of his professors, although his father wanted him to study law.

  Trembley and Bonnet had been writing to each other for some time, sharing their natural history discoveries and honing their observation and description skills. Bonnet had devoured every page of Réaumur’s insect volumes as soon as he had access to the library in the Geneva Academy, and at the age of fifteen he had written directly to the Parisian insect master, sending him detailed and imaginative descriptions of the behavior of caterpillars, antlions, and spiders. He and Réaumur had been in correspondence ever since. A third friend of Trembley’s, Pierre Lyonet, thirty-four years old in 1740, also of Genevan-French descent, lived a mile away in The Hague, where he worked as a lawyer. When he was not preparing legal cases, he spent his time dissecting insects. All three men were obsessed with insects, and with insect sex. All three were in correspondence with Réaumur and with one another.

  In Geneva, Bonnet, now nineteen, bored with his law studies at the Academy, had determined to try to solve the mystery of aphid reproduction, a mystery that Réaumur himself and numerous predecessors had failed to crack. Despite many efforts and experiments, he had not yet found a male aphid, he complained in volume 3 of his insect book, nor had he seen any act of aphid coupling. He was completely mystified. He challenged all young naturalists to solve the mystery of aphid reproduction. Lyonet also set up aphid experiments in his rooms in The Hague at the same time, but with his legal work, he could not watch his aphids day and night as Bonnet could do in his student rooms in Geneva.

  It was young Bonnet who made
the first breakthrough. On May 20, 1740, he placed a single newborn aphid on a branch of an evergreen shrub called the spindle tree inside a glass flask sunk in a container full of earth. His task was to guard and testify to her virginity. Always quick to make dramatic classical analogies, he compared his aphid to the virgin Danae in Greek myth, who was imprisoned by her father in a tower because he had been told her child would be his murderer. Between May 20 and June 24, Bonnet watched the newborn aphid moving around her glass tower through every hour of the day to ensure that no one tampered with his experiment and thus ensure that she remained a virgin. “I have been an Argus more vigilant than the one of the fable,” he wrote, referring to the giant watchman of Greek mythology who was reputed to have a hundred eyes.

  Astonishingly, Bonnet’s imprisoned female aphid not only survived her first molts but also actually gave birth on June 1. Over the following twenty-three days she produced ninety-four more aphids. In July, Bonnet sent his meticulous records and tables of findings to Réaumur by letter. He was not the first human to have witnessed a so-called virgin birth, a form of asexual reproduction that requires no fertilization by the male (now known as parthenogenesis),* but he was the first to record proof of it through repeated experiments, crowning seventy years of investigations and experiments by others working in different entomological traditions.

  In July of that year, Réaumur read Bonnet’s letter and findings to the assembled members of the French Academy of Sciences, established in 1666 to encourage and protect the spirit of French scientific inquiry. The audience, though respectful of the young man’s meticulous observation and recording skills, agreed that they could not confirm the discovery of virgin births in aphids until the experiments had been repeated and witnessed by others. Réaumur wrote to his friend the doctor Gilles Augustin Bazin in Strasbourg and to Abraham Trembley in The Hague to ask the two men to repeat Bonnet’s experiments with several different species of aphids. Trembley accepted the task, proudly explaining to the Bentinck boys, as they angled the microscope arm onto the glass tower that housed their own imprisoned aphid, that they were now engaged in a serious investigation that might put their names into the annals of science.*

  Within weeks, he and the Bentinck boys, Bazin, and Lyonet had all verified Bonnet’s discovery; they had all witnessed aphid virgin births for themselves. In August 1740, Réaumur sent Bonnet a letter of congratulation. Not only was Bonnet the first human to have both witnessed and recorded a virgin birth; he had toppled one of the central premises of eighteenth-century science—the belief in the universality of sexual reproduction. “These are assuredly observations of great importance in natural history,” Réaumur wrote to Bonnet, “since they teach us that the law of coupling is not a general law.” He appointed Bonnet to a prestigious place as a corresponding member of the Academy.

  For the rest of the summer, the carpet moths, Bonnet’s extraordinary aphid discovery, his own aphid verification experiments, and the boys’ lessons occupied all of Trembley’s attention. In late September he and the boys watched the first two carpet moths hatch; proudly he sent Réaumur a detailed description of the moths’ life cycle and enclosed some specimens. But for Réaumur the carpet moth was old news. He had already studied the genus, he replied apologetically, and had already published a description of its generation in detail. Trembley and the boys dejectedly released the moths and caterpillars, but Bonnet’s aphid discovery had given the young tutor a desire to test other supposedly natural laws: “A fact such as the one which aphids presented could only inspire in me a great deal of distrust of general laws,” he wrote. “I felt strongly that Nature was too vast, and too little known, for anyone to decide without foolhardiness that one or another property was not found in such and such a class of organised bodies.”

  Meanwhile, all through the summer, the water creatures had continued to thrive in their jar on the windowsill, largely unobserved—“Almost the whole of the month of September 1740 passed without my giving them the least attention,” Trembley wrote—until one morning he noticed that the tiny green creatures had all congregated on the sunlit side of the jar. When he turned the jar away from the sun, the water creatures migrated slowly back toward it. Could these minute beings actually be sentient? Curious and still baffled, he told the boys that for the next few weeks this creature—whatever it was—would become their new object lesson. Using a range of microscopes, they would investigate everything about it: what it ate, how it reproduced, how it moved. They would describe in detail everything they observed, and when they had recorded everything that was knowable, they would send a report to Réaumur, and then perhaps he would grant them the same honor he had granted Bonnet.

  The investigation began. First, he told the boys, they must determine one way or the other whether the creatures were plants or animals. Might those “tentacles” be branches or roots rather than “arms”? The only way to answer this question was to cut the creature in half, for only plants could survive being cut in two. “It was on the 25th November 1740 that I cut the first polyp,” Trembley recalled. “I put the two parts in a flat glass, which only contained water to the height of four or five lignes. It was thus easy for me to observe these portions of the polyp with a fairly powerful lens.… The instant that I cut the polyp, the two parts contracted so that at first they only appeared like two little grains of green matter at the bottom of the glass.” The creature did not die. To Trembley’s astonishment, “the two parts expanded on the same day on which I separated them.… I saw it move its arms; and the next day, the first time I came to observe it, I found that it had changed its position; and shortly afterwards I saw it take a step.”

  The flexible ball-and-socket-armed structure of the aquatic microscope that Trembley invented in 1745 allowed him to observe the polyps in movement and from every angle.

  Abraham Trembley, Memoires (1744)

  It was important not to jump to conclusions, Trembley warned the boys. They must watch and record everything just as Bonnet had done, just as Réaumur insisted. They might only be witnessing a feeble remnant of life, or perhaps they had cut off a nonvital section like a lizard’s tail. It was too early to say. But over the next few days, as the boys sketched diagrams of what they had seen, the two halves of the polyp continued to move vigorously, one with the original set of the hornlike crown of arms and the other without.

  Now Trembley was losing sleep. But there were stranger transformations yet to come. After nine days, the hornless, armless half of the cut creature began to sprout what looked like small arms. “Throughout the day I continually observed the points,” he wrote; “this excited me extremely, and I awaited with impatience the moment when I should know with certainty what they were.” Within a further week neither he nor the boys could tell one half from the other.

  Plants do not walk. Animals do not regenerate themselves. But the pond creatures did both. Alarmed, Trembley wrote directly to Réaumur, summarizing what he and the boys had seen and enclosing some early sketches. “I saw these parts walk, take steps, mount, descend, shorten, lengthen, and make so many movements, which up to the time I had only seen made by animals. I did not know what to think,” he exclaimed. Now he needed the philosophical big guns. He needed others to help unravel this enigma.

  Meanwhile, on December 18, 1740, Bonnet wrote from Geneva to tell Trembley that he had discovered a male aphid. It was rampantly sexual, he wrote, “perhaps one of the most ardent that there is in Nature. It appears to me that it does nothing except have intercourse as soon as the day arrives.” Had they been wrong about the virgin births? Surely virgin births and sexual coupling could not coexist in the same species? There were only two possible explanations that Trembley could suggest. Might aphids mate invisibly inside the womb? he asked. The alternative was even more bizarre: “Who knows if one mating might not serve for several generations?” he asked his friend. They should rule nothing out. Nature was proving more extraordinary than anyone had anticipated. Still he told Bonnet nothing abou
t the polyp experiments.

  On receipt of Trembley’s letter and drawings in January 1741, the incredulous French professor urged Trembley to send fifty of the polyps in a sealed jar to him in Paris as soon as he was able. Trembley packed up a jar and sent it with a servant on horseback to Paris, a journey of seven days. Only now that Réaumur had taken his claims seriously enough to send for the polyps did Trembley write to tell Bonnet about his “little aquatic being.”

  The creatures arrived in Paris on February 27 dead, suffocated in their glass jar by a too-tight seal of Spanish wax. Réaumur, frustrated, wrote to ask for more, suggesting that this time Trembley use cork as a sealant rather than wax and asking permission to read the letter to the savants in the French Academy of Sciences. Trembley, determined to make his experiment transportable, sent the count’s servants out on horseback on a trial run for miles across the dunes carrying the creatures in various bottles with different sealants. While he awaited their arrival, Réaumur read Trembley’s letter to the Academy at three consecutive meetings, on March 1, 8, and 22. Anticipation ran high. On March 16, Trembley, satisfied that he had now found the right traveling arrangements, sent off another batch of twenty water creatures from The Hague to Paris; this time they survived.

  A few days after he had dispatched the second batch of animals to Paris, Trembley received an excited congratulatory letter from his nephew: his “little aquatic Being ought to be regarded as one of the greatest marvels that the Study of Natural History can offer,” Bonnet wrote. “One can say that you have discovered the point of passage from the Vegetable to the Animal. What you have reported is close to an enigma, which I do not know how to decipher. But I easily console myself when I see that the clever men here, even learned men, such as our Professors to whom I have been very pleased to show your letter, are confounded.” Despite Bonnet’s advice to Trembley not to get caught up in metaphysical speculation and always to follow Francis Bacon’s rule of thumb to avoid hypothesis and stick to collecting facts, Bonnet’s mind had begun to spin. His was not the only one.