“Yet another continent of life remains to be discovered, not upon Earth, but one to two hundred feet above it…. At present we know almost nothing of it. Up to now gravitation and tree-trunks swarming with terrible ants have kept us at bay, and of the tree-top life we have obtained only unconnected facts and specimens.”
WILLIAM BEEBE’S TROPICAL WILD LIFE IN BRITISH GUIANA (1917)
Copernicus theorized that the Earth revolved around the sun, but it was not until he lay on his deathbed that he published anything regarding his discovery. He had largely kept it a secret, and a pretty good one as they go.* It would take Galileo to publicize and add nuance to Copernicus’s theory, but soon what was once heretical, that the Earth circled the sun, seemed obvious. Our place in the universe changed in a generation.
The biological equivalent of the Copernican revolution would prove less simple. The biological world does not revolve around us, but we still tend to believe it does. It took Linnaeus, and those who followed, to relegate humans to just another slot in the organizational cabinet of life. It took Leeuwenhoek to show us the microbes and their diversity. For the public, however, both of these realizations—that life is smaller than we imagined, and that we are a smaller part of life than we imagined—would come slowly and with difficulty. There would be no single person to convince us all of our marginal position in the biological universe, no simple change of perspective. In the end, it appears far harder to conceive that we are not at the center of the biological world than it is to believe that we are not at the center of the universe.
Because this biological revolution, let’s call it Leeuwenhoek’s revolution, is not complete, we are able to be surprised anew each time we find the world more diverse than we thought it was. We are consistently surprised to learn that most of life is not like us. We continue to assume ourselves average only to be reminded by each new discovery that we are not. It would happen to Linnaeus’s students when they went to the tropics. It would happen to Terry Erwin (another of Linnaeus’s disciples, though many generations removed) when he decided to kill all of the insects in the canopy of a tall, tropical rain forest tree.
Linnaeus never made it to the tropics, much less to the tropical forest canopy. He was poor at travel and ill-disposed to leave home for more than a few days. Instead, he would send out his students to do what he would not. Linnaeus called his students, sent around the world to find new and useful species, his apostles. He implored them, “don’t be afraid of exposing yourself to some degree of danger…anyone who hopes to reach a glorious goal must take many risks,”1 despite his own, consistent behavior otherwise.
The apostles were to collect everything vegetable, mineral, or animal. Useful things were to be valued over useless things. And every apostle tacitly knew, having gone to the field with Linnaeus and having seen his ordered collections, that Linnaeus did not just want a few species here and a few there. He wanted them all. The specimens were to be shipped home, where Linnaeus would name each one himself. Because his framework was by this time firmly in place, he could add species easily to the great library of life. New specimens could be quickly grouped and, once grouped, named. Collections from faraway places would not simply be stuffed in drawers, as they were before. They would be ordered.2 Linnaeus had left room in his cabinets for the new species. Now it was time for his apostles to do their job and collect the world for Linnaeus who, if they were apostles, was their implied god.
Christopher Tärnström was the first apostle to leave. He had worked with Linnaeus around Uppsala, and was one of his best and favorite students. He was older than his teacher, married and with children, but he wanted to go to China—for science and for Linnaeus. In 1746, Tärnström set off in one of the Swedish East India Company’s ships. He arrived in what is now Vietnam. The land was terrible and wonderful. It was thick with tropical possibilities. It was among these possibilities that Tärnström would die of a tropical fever, within a week of arriving. He had not yet collected a single plant. Linnaeus grieved, and then sent a new apostle.*
Of Linnaeus’s seventeen apostles, five would die before returning from their first trip, most of disease. Hasselqvist died after returning with many hundreds of new species, nearly all of which would bear Linnaeus’s name. Löfling, another of Linnaeus’s favorites, would die after having achieved a quick fame in the Venezuelan port of Cumana. He, like Tärnström, succumbed to a fever.†
Even for those who did not die, the going was not easy. In Japan, Thunberg was put in an island camp for foreigners. His host did not allow him to leave and so he reached under the fence for new plants. Instead of eating his meager rations, he dissected them to see what plants they had come from. The apostles were to collect specimens no matter the circumstances.
Despite the odds, many of the apostles were successful. Solander, who went on an expedition with the great botanist Joseph Banks (and who was the only one of the apostles whose species do not bear Linnaeus’s name), would become the model for the biologists who accompanied future trips to sea. Charles Darwin would follow in Solander’s shoes, as would every subsequent field biologist and taxonomist. More to the point, because of the success of the Linnaean system, every biologist would, in a manner of speaking, be one of Linnaeus’s apostles. Every future biologist would use Linnaeus’s genus-species system for names. Every future botanist and many zoologists would look to their specimen’s sexual organs as a means of identification.
Most of the original apostles focused on plants, mammals, and birds. Microbes were ignored entirely and insects were a low priority. They were more difficult to identify than plants or birds and seemed to inspire a kind of anxiety. Daniel Rolander was one of the few apostles who spent time on insects. Linnaeus sent Rolander to Suriname on the northeast coast of South America. Suriname might still hold an unnamed species or two or, as an outside possibility, hundreds of thousands. The trip seemed to start well enough. Rolander wrote to Linnaeus, “I now am allowed to wander in Surinam, an Earthly paradise, and see the great God’s greatest miracles in Nature.”
For Linnaeus’s apostles, nearly every place they might go in the world was more full of species than Sweden. Tärnström thought southern Spain to be an “Earthly paradise.” 3 Suriname, though, was something else entirely, something more exotic than Spain. It was quite possibly, for a mind conditioned on Sweden’s sparse diversity, too much. Rolander’s reports home began to take on ominous tones. Rolander wrote, “I am pretty sure that even you, Sir, on neither the first nor the second day, would dare to walk into the forests, for you would see big snakes, lizards, insects and other animals…[which] with open mouths and terrible roars throw themselves at the passerby. I do not want to mention the thorny trees and bushes that everywhere catch one, so that one cannot escape…. fallen and rotting fruits spread a stench that can kill.” He concluded, “For here not everything seems to be made for the sake of man.”4 After this letter, Rolander grew overwhelmingly terrified of what was around him. According to one version of the story, he left Suriname long before he was supposed to go home and very long before he had finished collecting everything Linnaeus desired.
Linnaeus had told Rolander to bring back useful things. He told Rolander that most of the species on Earth had been named (and by him, no less), so his job would be to collect the few additional species he might find, to fill in gaps. Instead, Rolander found many thousands of species just around his quarters. Many were plants, but most were insects. The insects called to him, at him even, in a din. It was all he could do to grab a few and put them in jars, and the prospect of doing more was overwhelming. He stood before a great wave of life. It threatened to devour him and in the version of his story told everywhere until very recently, this is what happened: Rolander went mad in Suriname, came home to drink and homelessness, and was never heard from again. This story was not true, but it masqueraded as truth for centuries.
Linnaeus had lied about Rolander, but no one knew until the spring of 2007 when Rolander’s seven hundred pages of journals—long hidden in a botanical library at Denmark’s Natural History Museum in Copenhagen—were translated and read for the first time.5 From the translations of Rolander’s journals, it appears that he had collected many thousands of specimens. He then returned to Sweden, specimens in hand, and refused to give them to Linnaeus. Linnaeus did not respond well, and proceeded to blacklist Rolander. He prevented Rolander from getting work and even broke into Rolander’s house to steal some of the Suriname specimens that he particularly wanted. Rolander eventually found a teaching job that did not allow him the opportunity to publish his results. He never, it appears, turned to madness or drink. He just turned to the quiet unknown, where Linnaeus would deal him a final blow, one that was suited to his obsession. He named a European seed bug species after him, Aphanus rolandri, with rolandri for Rolander and Aphanus, Greek for ignoble and obscure.
Although Rolander found hundreds, perhaps thousands of species, as a consequence of Linnaeus’s blacklisting nearly all of those species went unnamed and their whereabouts are now unknown. Linnaeus named a few species, perhaps those he stole.6 Those species included a beetle that had caught Rolander’s eye. It was black with a red band just below its head and would ultimately be named by Linnaeus, Galerita americana, the first species of carabid beetle to be named from the neotropics. Rolander was largely lost to history, but that beetle species lives on. For now, the beetle and the few other named forms from Rolander’s trip would be the few rare gems from the Amazon to which European science could cling. But it would not be the last beetle collected from the tropical forests of the New World, not by far.
The beetle that Rolander discovered is from a lineage that, despite its name (the “ground beetles”), we now know lives primarily in the tropical forest canopy. Although many collectors, Rolander included, would turn up an occasional species from the forest canopy, no one had collected very extensively, particularly in the upper reaches of the tall tropical trees. Such exploration would wait another two hundred years. Beginning in 1971, Terry Erwin was to be one of the first people to take a close look at the insects of a forest canopy. He would not only find more ground beetles,* but also, much, much, more.
Terry Erwin grew up in coastal California. He was born on December 1, 1940, some 233 years after the birth of Linnaeus. As a boy, Terry Erwin liked fishing with his grandfather. He and his grandfather would drive into the high Sierra Nevada of California early in the morning. His grandfather would pack a small lunch and they would settle on their boat, waiting for the water to kick up a treasure or two. Some days they filled a basket, and some days they went home empty-handed. Terry and his grandfather just lowered their hooks, applied the requisite skill, and waited.
Back home, Terry Erwin’s father raced cars. Upon meeting some boys it is easy to project forward to see the man they could become. What would Erwin’s peers have seen in him? As he got closer to finishing high school, Terry Erwin founded the California Conquistadors, a hot rod club. He too raced. If there was an obvious path for Terry Erwin it could not possibly have been to the rain forest canopy.
To the extent that Terry Erwin thought at all about the rain forests in high school, he might have thought about exotic lands filled with half-naked natives. He might have imagined them through the lens of National Geographic. The plight of the Amazon was not yet big news nor was its diversity. The last century’s naturalists had found great riches in the Amazon, but they had been all but forgotten.
When he finished high school, Terry Erwin enrolled at San Jose State College. He soon found that he deeply enjoyed biology, and came to appreciate that the biological world could offer some true marvels. Put down your hook and you may catch a big idea, or a new species. Then, as now, most biology students studied medicine or veterinary science, and this might have seemed like a logical trajectory for Erwin as well. But instead, Erwin, like Swammerdam before him, was drawn to insects. Their parts were as intricate as the machinery of an old Mustang. In the same way that Terry Erwin had learned to take an engine apart, he would begin to take insects apart, drawing their component pieces, testing their function, and comparing their ways.
Erwin took his first entomology classes from Professor J. Gordon Edwards. Edwards would become his earliest of many scientific mentors, a figure he would consult many times in the decades to come. Edwards is best known as an early critic of the movement to ban the pesticide DDT (he sometimes began class by putting a sample of DDT in his mouth to demonstrate its safety), but he was a man of many interests. Many knew him as a mountaineer. He pioneered many hundreds of climbs to summits in Glacier National Park, and would eventually die of a heart attack while climbing there. Some thought him a kind of explorer. As a young professor, Edwards took off on foot across Mexico and in the process discovered several new ruins. To Erwin though, Edwards would always be a beetle biologist.
As a student with Edwards, Erwin learned to identify different groups of insects in the field and in the lab. He learned how to arrange them in a collection—the careful rituals of the entomologist tribe. Through these rituals of collection and study, he gained a sense of how much was unknown. Edwards would eventually convince Erwin to do a project on beetles. The bombardier beetles were poorly organized, poorly grouped into Linnaeus’s bins and no one else seemed to be working on them. Erwin would begin the beetle project, which would turn into his master’s thesis at San Jose and then broaden, subtly, into his life’s work. He would organize the bombardier beetles of California in their proper Linnaean bins, naming species where necessary, combining species where it became clear they were not different. It was an ambitious project for a young master’s student, one that could take decades. Terry Erwin had two years.
The bombardier beetles are unique in many ways, but the trait for which they are best known is their chemistry. When threatened, the beetles expel a boiling hot defensive spray, which they can aim at their assailants (from 1965 on, said assailant very often being Erwin). The beetles produce the spray by mixing hydrogen peroxide and one of several other highly reactive compounds. They can fire up to seventy pulses of the spray in just a few seconds. There are five hundred or so species of bombardier beetles on Earth, each with its own particular set of defensive compounds.
Erwin needed to organize the California species for his master’s thesis, but as he looked out at the world it was clear that many more species remained. He was intrigued by the beetles’ evolution and ecology, but as much as anything enjoyed the process of taxonomy and systematics. Like all of the systematists before him, Erwin separated the different beetle species based on their genitalia. Much depends on the shape of the clasper (used to hold the female during mating), the arc of the phallus, the curve and bow of the aedeagus (which secretes sperm) and so on.* Systematics requires great patience and a memory for these and other details. It is thick with traditions that go back to Linnaeus and before, traditions that dictate how things must always be done. Erwin was hooked (or, perhaps better put, clasped). He would not go another day in his life without thinking about beetles and their intricate parts.
Terry Erwin would do everything he could to learn more about beetles. As a measure of his growing focus, his letters to colleagues and friends in the years that would follow were overrun with beetles—new species, strange species, and hard to distinguish species. He surely had begun to dream of beetles, to think of beetles in both his working and free moments. Terry Erwin would travel new places and with that travel would come, of course, new beetles. Some people go to Europe and write home about the food or the mountains. Erwin wrote about insects in museum collections.
Erwin’s trajectory started out as a rather standard one for academics. He went to the University of Alberta in Canada to write his dissertation with the carabid beetle expert George Ball. He was offered a fellowship at Harvard and then took a position at the Smithsonian Institution that allowed him to go to Sweden for a year where he would work with the famous (in beetle circles, anyway) Carl Lindroth at Lund University. He would write that it was his “first experience with a fully known and understood fauna.”7 Erwin was set to establish himself in Linnaeus’s landscape with an eye toward those small species that Linnaeus had paid less attention to, that he might, if very lucky, fill some new Swedish beetles into Linnaeus’s cabinets.
Had Erwin stayed in Sweden, he might have made a lifetime out of studying the beetles of those cold lands. He might have answered many small, unresolved questions. It would have been a respectable contribution, but fate was soon to pull Erwin south, more along the tracks of Linnaeus’s apostles than in Linnaeus’s own footpaths. He was to travel to a land he would never fully leave nor completely understand. It had not been his plan, but soon it would be his life.
It happened suddenly. Before he left Sweden, Erwin had written a grant proposal to do more work on the systematics, life histories, and so on of the ground beetles of California. Paul Hurd, Erwin’s department head back at the Smithsonian, reviewed Erwin’s proposal. It was a logical continuation of Erwin’s earlier work, and certainly seemed a worthy project. But Hurd had other ideas. He knew that there was money for work in Central America, but not California, and so without Erwin’s knowledge he scratched out California, wrote “Panama” in its place, and submitted the grant. Erwin came back from Sweden and at a general staff meeting it was announced that he had received a grant to pursue his research in Panama.* It was the first he had heard of it, and he initially wasn’t sure what to do.8 By December of 1971, a few months after he had first heard about the grant, Terry Erwin was on a plane. He could not complain. At some point, he bought a machete, a hat, and a notebook. Soon, though not quite yet, he would also buy (his old advisor Edwards perhaps in mind) a great deal of pesticide.
When Erwin considered what might lie ahead of him in Panama, he thought almost exclusively about which beetles he might find. His advisor, George Ball, had worked extensively in Mexico and so Erwin could imagine what one might find by going farther south. But he also had other forbearers. Since Rolander’s travels to the neotropics, a great deal had been learned about the area. That knowledge was due in no small part to the work of two collectors with a special fondness for beetles, collectors to whom Erwin would soon find himself compared. Almost two hundred years before Erwin headed to Panama, the exploration of the neotropical forests had begun in earnest. In April of 1848, Alfred Russel Wallace and Henry Bates followed Rolander into the tropics (limping along a little later—already sickly, whiny, and fortunate—would be Charles Darwin). These men were Erwin’s expeditionary ancestors. They would travel in search of new species, with little in the way of compensation other than their room and board. As scientists, they began as amateurs. As collectors, they were unrivaled.
Bates and Wallace left cold Great Britain together on a boat for Para (now Belém), Brazil. As the boat pulled into the dock, they began collecting almost immediately. Belém was, like Riberalta in the northern Bolivian Amazon today, a wide flat city of one-story houses, dirt roads, and subsistence. In a few decades there would be opulence both in Belém and farther upriver. Opera houses would be built and decorated with thousands of hand-painted tiles imported from Europe. European opera stars would come to sing arias mere feet from where the Amazon played its sounds over the ancient mountains. Indigenous people would haul rubber on their backs down to the riversides, where it was floated to Belém. From Belém, it went to North America or Europe. This trip of the sap—tree blood of a widespread Amazonian tree—via the veins of commerce would make some men rich and many others dead. But not quite yet. For now, the towns were surviving, living off animals and trees, small fields, and the fruits of the hot land. Butterflies and beetles still flew down the streets.
Bates and Wallace would find remarkable diversity in the local wildlife. Wallace would soon write that “the more I see of the country, the more I want to; and I can see no end of the species of butterflies when the whole country is well explored.”9 Like Linnaeus, they craved rare things. Unlike Linnaeus, they were fully willing to risk their health to find those things. Their passion for these species was close to limitless.
Linnaeus had named roughly ten thousand species. Many, perhaps most, of those species had earlier been named by someone else or at least collected by someone else and nearly all were European species. Bates and Wallace would go on to collect thousands of new species each, most of them insects. In their first year in Belém, Bates would collect more than seven hundred butterfly species, many of them from very near the city. Each day Bates and Wallace would draw what they had found. Their notebooks from this time are so eager, so intense and full of awe at what they were finding that they seem almost to vibrate. On each page are dozens of species, artfully depicted at the end of the day in the tropical heat. Again and again they reiterate what they see, “species of endless diversity.”10 They went to sleep, their minds still alive with legs and bodies, antennae and tarsi, the multitudinous articulations of joints that they would find walking through the litter of the forest floor, and finally up into the unreachable trees.
Linnaeus had complained almost without end about the travails and loneliness of being away from home for several weeks. Bates and Wallace would rarely complain during their many years in the tropics, despite frequent sickness and general lack of comfort. They were, more often than not, giddy with the delight of their days.
Bates and Wallace would eventually separate. In 1849, Bates went on to the small town of Tefé fourteen hundred miles upriver, where he would live for many years collecting samples in his backyard. It was only after some time there, long removed in space and time from Europe, walking barefoot, in tatters of clothes and subsisting on dwindling food supplies, that his letters offered a moment of discontent. If only to express his humanness, Bates wrote, “I was obliged, at last, to come to the conclusion that the contemplation of Nature alone is not sufficient to fill the human heart and mind.” The implication was that it had, however, come damned close.
Bates, however, would continue his work at Tefé and elsewhere in the Amazon. He clearly must have found whatever nature needed to be mixed with, in order to fill the human heart and mind. He would collect, around Tefé alone, more than five hundred species of butterflies. He would spend, all told, eleven years of his life in the Amazon. Bates, together with Wallace, had found diversity in the Amazon to a degree unknown by anyone who came before (except the locals, of course, who were not aware they had anything special).
With Bates just settling in to Tefé, Wallace headed home, too ill, too broke, and perhaps finally too homesick to continue his work. In 1852 he made the journey back from his collecting sites down the Rio Negro all the way to Pará, Brazil. He had intended to bring with him many living animals to take back to England, but there would be complications. Some escaped. A monkey ate some of the birds. The journey was arduous, and, given his company, probably a little noisy. But things would get worse. In Pará, Wallace would learn that his brother Hebert, whom he had brought to Brazil, had died of yellow fever. He was devastated, and things would get worse still.
Wallace boarded his ship for home: the Helen, named for that beauty from Homer’s Odyssey, cause of wars and sinker of ships. The specimens from the last two years of Wallace’s collections had not yet been sent ahead to England. The samples were stopped in Manaus, and would have to travel home with him along with the remaining monkeys, macaws, and parrots. More work, more difficulty, more travail. On August 6, 1852, after three weeks at sea, Wallace was sitting in his cabin reading when the captain came in and calmly said, “I am afraid the ship is on fire. Come and see what you think of it.”11 Wallace and the captain proceeded to look for the fire, which they found in the forecastle. The crew worked to put it out, but to no avail. A hole was cut in the cabin floor to allow water in to put out the fire. The fire continued unabated, however, and now so did the flooding from the hole.
Wallace had with him everything of value from his years in the Amazon, but surely the most valuable were his specimens. But as the boat rapidly filled with water, he had only enough time to grab a couple of shirts, his drawings of fishes and palms, and a few valuables before jumping into a lifeboat. He did not grab his specimens—there were too many and he could not even contemplate where to begin. Wallace and the crew waited in the lifeboat, with the hope that the fire might still go out. It did not. The leaky lifeboats were lowered into the water, where Wallace’s fate was by no means assured. The ship would sink within a day, taking nearly all of Wallace’s specimens and his modest menagerie with it. One parrot escaped the flames and fell into the water where it was rescued. Wallace, the captain, their shipmates, and the one lucky bird floated together in the middle of the ocean for more than a week.
Eventually Wallace and the entire crew were rescued by a freighter, which itself almost sank. He returned to England, nearly all of his work over the last years lost. He would take time to mourn his brother, gather his life together, and continue with his work. It was perhaps because of this hardship that he would decide to go on a new expedition, this time to Malaysia.
In Malaysia, Wallace would find his greatest success. It was here where he would turn from obsessive collector to genius; where, in the fevers of malaria, he would dream of species changing forms, one bird of paradise changing into dozens, one monkey turning into multiple kinds of monkeys, one primate changing into man. Wallace would write to Bates, who was still collecting in the Amazon, of his new “Law which has regulated the introduction of new species.” Wallace offered a clear vision of natural selection. Species changed. Those changes were brought about by the survival of more fit, more fecund, individuals. The diversity of life on Earth had come into existence through a great many such changes.
Bates saw from these letters that Wallace had revealed the process that engendered the species Bates found all around him. Bates sensed that what he already knew was clarified. He wrote Wallace back with congratulations and then got back to work. He stayed long in the Amazon. Bates would eventually come home with almost 15,000 species, among which were 52 mammals, 360 birds, 140 reptiles, 120 fish, 35 mollusks, and a whopping 14,000 insect species, most of which were beetles and more than half of which were newly named by Bates.*
Here, in the collections of one man, were more species than had been discovered by Linnaeus and all of his apostles combined. Leeuwenhoek had found a partner in his mania. There are not 14,000 species in all of Sweden, or for that matter all of England (excluding samples from elsewhere in museum collections). Though Bates wrote a book about his travels, the most lasting impact of his work was his collections. The beetles were particularly astounding. Bates had always been a beetle man and the Amazon had turned out to be a beetle place. The unanswered question in Bates’s collections was how much was left. There were two ways to view the collections he had made. On the one hand, that he had collected so many species suggested that there were fewer left. Drinking a sip of water from a cup leaves less for later. But the other possibility was that he had collected so many species because there were so many to collect and so many more left. Drinking a sip of water from the ocean leaves plenty in which to drown. It is clear in retrospect that Bates had discovered an ocean of life. Upon reaching Panama, Terry Erwin would find out how well he could swim.
Before Linnaeus, humans were at the center of the biological world. Linnaeus’s system was revolutionary in its ambivalence with regard to man’s position. Man was given a genus and species, just like the red oak (Quercus rubra).† As Linnaeus described more and more species, humans became a smaller and smaller slice of the pie. We were one of a hundred, then one of a thousand and then one of ten thousand species. With time, even Leeuwenhoek’s tiny creatures would be named and they too would become recognized as species. By comparison, we would become even larger and more lumbering, so much so that we became unable to see much of the life around us. It had been invisible, and then made visible, and then once we realized we had been missing it, there was, for a moment, a kind of awareness of our ignorance.
Even once microbes had been discovered, we found it easy enough in daily life to go back to believing we were still central figures in what was then thought of as God’s creation. We knew there were microbes, but as always, we acted as though our lives were the important ones, and our moment in time the crucial one. Show me a universe with ten thousand species, a burgeoning of tiny life-forms, and millions of years of history, and the story will always be about the storyteller—in this case, us. This tendency to see ourselves as central means we miss obvious things around us. When he arrived in the tropical forests of Panama, Erwin was, like everyone else, missing things. He just did not yet know exactly what or how much.
Erwin headed to Panama with the idea of looking for ground beetles, carabids, up in the trees. No one had any idea, really, what he might find. Rolander had collected the first neotropical carabid, Bates had collected many in between, but what was left to name was, at best, unresolved. The canopy was still mysterious enough that it would not have been surprising to find just a few species of ground beetles there, the same species in every tree. In Sweden, a single tree might hold no more than a dozen species of beetles. The trees and forests of Panama, while wetter, were not so different from the big old trees of Sweden. It was not obvious that any more diversity should be expected, and anyway, Terry Erwin was not after diversity—he was just after a few beetles. That is all that had been called for in his grant and all he, as a biologist, had ever done.
Erwin left for Panama for the first time in December 1971. He was gone just a short time but came back nearly beyond words. Erwin had not brought equipment for climbing, but while in one higher-elevation forest he had scrambled up an, apparently, short tree and thrown down a couple of big bromeliads, a kind of flowering canopy plant, kin to the pineapple.* His wife, La Verne Erwin, put the bromeliads on a sheet to wait for beetles to climb out. Terry later came down and started beating one of the bromeliads to help scare the beetles out faster. What came out, though, was not a beetle but a viper. After having been thrown a viper from up in the tree canopy, La Verne Erwin was not very excited about the prospect of more canopy work, but Terry Erwin had found beetles in those branelids. He would be back.†
Terry Erwin was to return to the canopy in May of 1972 in order to compare the beetles of the ground and the canopy. But he would study the canopy of lowland tropical forests this time. Unlike those of the high elevation forests, the trees in Panama’s lowland—moist, tropical semi deciduous forest had their first big branches at sixty feet or more above the ground.12 Erwin would have to scale the trees with a belt and shoe spikes until he and other collaborators in Panama could build ladders and platforms for observation in the trees. Erwin wrote a note to one of his growing number of mentors in beetle biology, Carl Lindroth, “I start taking ‘monkey’ lessons soon.”13
When Erwin began this work, few biologists before him had climbed high into trees. Some simply free-climbed (free climbing is what happens when competitiveness and pure machismo mix with a little ego). Someone lets out a barbaric yelp, skins his (more often than not) knees and looks around from the top for the woman who he had hoped was watching when he began climbing. These biologists had already made it into tropical canopies, but once there they had only fleeting glimpses of the world they climbed up to see. They were actually quite clumsy among the other, more sophisticated tree dwellers. Monkeys appeared and then disappeared. Wasps appeared and stayed. These dangling scientists were as blind to what was farther afield as they had been from the ground. They were high enough to realize they were among something slightly magical, but they were not mobile enough to explore.
Erwin would eventually learn to climb and on his first expedition enjoyed modest success. From the “wonderful world of anteaters, sloths, and toucans,” he collected eight thousand individual carabid beetles, “mostly in their own habitat [i.e., no trapping] doing their own thing.”14 Many of those species had been found only in the climbs into the canopies. It seemed like more climbing was necessary, or at very least more sampling from the canopy—however that might occur. Erwin continued to climb trees and sample from the ground. Then, in 1979, he had a flash of insight and did what might have seemed obvious to an entomologist trained by Gordon Edwards, the defender of DDT: he started to spray pesticide into trees and then waited for his beetles to come down to him.15
As a kid, I had a persistent daydream that one day the ocean might dry up for a moment. I would run along the sea floor looking at each of the shimmering, flapping, shining, writhing, species.* The forest canopy, particularly the tropical forest canopy, was like the ocean. Its contents were invisible. If only someone could reveal it to us all at once, and show us the shimmering life above. The forest canopy was more than sixty feet above Erwin. Around him, thick buttresses steadied trees against the wind. The roots and litter on which he was standing were dark with morning and shade. Beginning in 1979, seven years after he first went to Panama, Terry Erwin laid out sheets beneath one big tree. He bought a few commercial insecticide foggers. Then one morning at 3 a.m., after the sheets had been put in place, with the wind still and the forest birds not yet calling, Erwin began to fog the tree canopy. He turned the fogger to get all of the sections of the tree. Soon the insects began to fall.
The insects drummed the sheets, one, two, three, four, and then the tick, tick, tick of the smaller things, accumulating.† Most of the insects had fallen within the first twenty minutes, but Terry Erwin watched for an hour as the last few individuals dropped from the leaves, bouncing from branch to branch as they fell. He finished the first tree and then fogged another and another and another. At the end of each day the sheets were folded up and carried back to the lab, where they were frozen both to kill the insects and to make them easier to store until someone could get to them.
Ultimately, there would be nearly sixty thousand legs piled on the sheets in the refrigerators Erwin was using. Among them were carabid beetles, snout beetles, leaf beetles, pleasing fungus beetles, lady beetles, handsome fungus beetles, click beetles, and then the ants—more ants than anything else. Erwin eventually needed to pull everything out of the sheets, put them in jars, and then sort them, but sometimes in the field he would have just stood over what had fallen on the sheets, looking. Something was being revealed to him here, albeit by force, in a way that no one else had quite seen before. He was on the verge of something, maybe something big, but just what was not yet apparent.
As Erwin counted and considered the insects he had collected, he would find himself with two kinds of problems. There was a Linnaean problem—how to sort, organize, and name the mess of things that had fallen around him. There was also a problem, maybe more of a struggle, that seemed to evoke Leeuwenhoek before his microscope. Here was an inscrutably diverse assemblage of things. Some had fallen down on biologists such as Rolander and Bates before, or turned up when someone had come across a newly downed tree, but there was so much more here than what people had imagined. Would that he could just pen a letter home to the Royal Society, “on some curious beetles discovered falling from a tree.”
The ordinary scenario for someone like Erwin, looking for carabids, would be that he would go home, work on his carabids for the rest of his life, and put everything—all the other beetles, grasshoppers, ants, etc.—in the corner for someone else to deal with someday. Entomology museums have thousands of such collections—messy jars of unsorted bugs from faraway lands. Once he was home with his new carabids, his only job would be to name the carabid beetles he found. For the most part, this is what Erwin did. He would soon forget about Linnaeus’s few Swedish beetles and lose himself in forests closer to those where Bates once worked. By now, he knew of Bates; he might have even hoped or imagined himself, on the best days, a kind of modern reincarnation.*
But what Erwin saw and what he wondered about was not just the carabid beetles. The animals that had fallen before him were dense, diverse, and, it became clear, mostly unknown. In seeing this unknown world, Erwin must have felt both delight and sheer horror at the diversity he had found. J. B. S. Haldane is said to have famously quipped, when asked what his research had allowed him to infer about God, that “the creator had an inordinate fondness for beetles.” Erwin had the growing impression that evolution did not just have a fondness. It was—like him—obsessed.
For two or three years, Erwin sorted the beetles collected in those first trees. There were so many specimens that many of the things that weren’t beetles rotted before they could even be processed. Erwin had fogged nineteen trees in total. He had enough specimens, enough new species, to last many years, perhaps his entire life. Who really knows why any person does what they do? It is easy enough to imagine Terry Erwin’s passion for beetles as an outgrowth of early forays fishing with his grandfather, combined with a somewhat obsessive personality. To do the work that Terry Erwin did must have been, at times, difficult. It is one thing to study birds day after day and have the positive feedback of a society that says that yes, birds are lovely. It is another thing to study bugs and hear at dinner parties only complaints about roaches. Terry Erwin kept on and, by every account, grew more fascinated, more deeply involved, more concerned with the jars of dead insects in his office and the trillions of living insects elsewhere in the world.
The insects enchanted Erwin not just in their own right but also for what they seemed to indicate about life’s dimensions. As he and his minions sorted specimens from the canopy fogging, Terry Erwin would wonder about the broader picture. If there were this many beetles in a few trees in Panama, might there not be even more in the Amazon, Papua New Guinea, the Congo, and the world as a whole? It seemed that every tree yielded something new. He kept being surprised. The sea of life that, in the original telling of the tale, had swallowed Rolander, might just threaten to swallow Erwin.
In 1980, Peter Raven, one of the world’s preeminent tropical botanists, participated in and led a National Research Council meeting to set research priorities in tropical biology. As part of the meeting and the resulting book, Raven made a crude estimate of how many species there were on Earth.16 Raven estimated that there were perhaps 2.5 million unnamed species, for a total of roughly 3.5 million species on Earth.* Raven and colleagues would go on to write that “increased emphasis on the study of certain groups that are relatively well known, such as butterflies and beetles, might be justified.” Raven’s estimate was a first. Earlier scientists had, going back to Bates and Wallace and even before, noticed that tropical forests were diverse, but never went beyond marveling at such diversity.17 There were many species, but just how many still seemed beyond approach.
In response to a letter from Raven, following the NRC meeting, Erwin started doing arithmetic. He did not believe that beetles were well studied and he did not believe that there were only 2.5 million unnamed species on Earth. He was not a mathematician by training and therefore the calculations were crude, but what he was seeing was so extreme that crude might do. Leeuwenhoek too, when confronted with the mad riot of life, had turned in some extremely rough numbers. Raven wanted to know what Terry Erwin, or anyone, might find in an ordinary drop of forest.
Erwin did a bar napkin calculation. He had, in the canopy of the nineteen individual trees of a single species, found nearly eight thousand beetles of twelve hundred species. From this starting point, he began simply. He estimated (that is, guessed) that 163 of the beetle species he found in the nineteen trees were so specialized that they would be unlikely to be found on any other species of tree. They were host (the tree being the host) specific. The other species, a little over a thousand, were regarded by Erwin as transients, species that fed on multiple species of trees. What if he imagined that every tropical tree species had 163 host-specific species of beetle unique to it? In a hectare of tropical forest with seventy tree species there might then be 12,000 species of canopy beetles (163 times 70). Assuming beetles represented no more than a third of all species, there could be a total of 31,000 species of canopy arthropod species in the same forest.* Put simply: in a backyard’s worth of tropical forest canopy—a drop—Erwin estimated there were three times more arthropod species than there are bird species in the entire world.
Erwin’s calculation, of the number of insect species in a hectare of tropical forest, constituted the majority of a not quite two-page article in the relatively obscure (OK, very obscure) Coleopterist’s Bulletin. It was outrageous and simple, but, to him, not obviously flawed. The next step was what would cause trouble. Erwin, as a kind of afterthought, multiplied the number of host-specific beetle species per tree species, based on his work with the Panamanian tree Leuhea seemanni,† by the number of tree species in the tropical forests of the world, 50,000. He then again accounted for the other species, non-beetles, and ground-dwelling species. If the host specificity of beetles on the one tree species Erwin studied was representative, “there might be 30 million tropical arthropod species in the world.” That sentence would, with time, make Erwin’s name synonymous with the debate about how many species there are on Earth, though it would take a while.*
Erwin is often remembered for predicting there might be 30 million species on Earth. His prediction was actually bolder. He had predicted 30 million species of tropical forest arthropods. He refrained from making the additional prediction of how many total species live on Earth. Erwin had already been bold enough. He did not dare to be any bolder.† Erwin, with one sentence, had increased the estimate of the number of tropical forest arthropods alone by threefold. Everything else—the fungi, bacteria, crustaceans, as well as the arthropods from every place but the tropics—would have to be tallied by someone else. Thirty million was a big enough number for him.
We can imagine how there came to be so very many species. We can imagine how it began. The verdant land was colonized by a bug or two. Those bugs moved from land to land eating the untouched wilderness of leaves. A single original species would have eaten all the plants, would have eaten seed, root, and leaf. With time other plants emerged, and as they did, so too other insects. The jack-of-all-trades could eat everything, but it could eat nothing well. Specialists evolved—species that ate just one plant species or just flowers, just nectar, or just seeds. And as plants evolved into more species, the insects evolved into more species, each plant with a few animals to eat it and keep it in check or, as pollinators and seed dispersers, to keep it alive.
Seen from a distance, this story of the plants and insects is the main story of the evolution of multicellular life. The dinosaurs and then birds, the mammals and fish are just the ringing bells of nature’s basilica. It seemed to Erwin that most species were plants and bugs. It might have been that way for tens of millions of years. We talk about the age of dinosaurs and the age of mammals, but from a broader perspective, since the first colonization of land there were all ages of insects and even smaller organisms. Dinosaurs came and went, but the beetles divided, one species becoming two, and conquered.
The immediate response to Terry Erwin’s paper was silence. Silence is the response to most scientific papers. The average biologist might write a few dozen papers in his or her lifetime. On average each of those papers will be referenced by another paper once, and read just a few more times than that. Science is replete with unread documents and entire lives of largely unnoticed research. This was, it seemed, the fate of Erwin’s paper in the Coleopterist’s Bulletin, a journal that, as you might have guessed, does not have a very high profile.
At some point though, perhaps as Erwin began to talk about the research, his estimate began to demand attention. Margaret Lowman, often called “Canopy Meg” for her pioneering canopy research, remembers first hearing about Erwin’s estimate at a meeting, where it was a major topic of conversation.18 Once the paper was noticed things happened fast. Responses to Erwin’s estimate fell into three categories: wonder (Lowman’s response), consternation, or outright aggression. Most people probably responded with wonder.19 But the aggressors wrote papers and were more vocal both in print and at meetings and so were more prominent in the debate that ensued. Erwin was, to say the least, surprised, and in one paper and then another was starting to feel the need to “clarify the situation.”20 The criticism was not of Erwin’s equations (though there was also some of that). Although simple, the equations were relatively unassailable. The question revolved around the numbers that went into the equations, and in particular the estimate of how many beetle species or arthropod species more generally are really restricted to a single tree species, so-called host-specific species. Erwin’s estimates of the number of host-specific species was, by his own admission, preliminary. Different assumptions about these values could yield much lower or much higher estimates of the number of insect species on Earth.
E. O. Wilson, the ant biologist/sociobiologist/conservation biologist/evolutionary biologist would, many years later, show a picture to convey the significance of Erwin’s estimate. It shows the world with animals drawn in proportion to their diversity. The token vertebrate, an elephant, is the size of a bacterium; the plant slightly larger and the beetle, meant to represent the insects, looms grotesquely big at the fore. Carl Sagan has described the lay of the land in our solar system similarly by saying, “there are four large bodies other than the sun, and the rest is debris.” The Earth, of course, falls under the category of debris. For Erwin, beneath his magical Leuhea trees, there was just one large body and it was the insects. All the rest was food and debris.
Erwin’s estimates were controversial, in part, because estimating something so basic as the number of species on Earth was not viewed as science. It was and is more like soothsaying, reading beetles in the leaves. Yet the estimates had important implications. To take a simple example, one might consider the value of insect species as medicine. Plants and animals all over the world have been shown to be valuable as traditional medicines, or, when derived, pharmaceuticals. If insects are no more or less likely to lead to medicines than any other taxon—probably a fair assumption—then most medicines should and could come from insects.*
To try to get around providing better estimates for the values in Erwin’s calculations, Kevin Gaston, a prolific English ecologist, tried a kind of shortcut. He did a survey of biologists. How many species of beetles do you think there are? How many species of mantis do you think there are? How many species of plants?
The answers rolled in with near unanimity. “There are slightly more species than we already know.” Even biologists who thought Terry might be right, believed their own groups to be reasonably well known. The answers were modest. We have only a little more to go. Linnaeus would have given the same answer. It was the voice of scientific skepticism, or perhaps modesty. Skepticism sees nothing until it has already been discovered. Who knows from what clay—what mix of observation and madness—new insights and theories come from? Such insights are not skeptical, well-mannered science. Skeptical, well-mannered science winnows. It attacks. It critiques. It builds slowly. It never leaps to conclusions or speculates wildly.
Perhaps Erwin was right, but he was now going to have to prove it. This, of course, he could not do. He needed data that did not exist and would not exist, not easily anyway. It had taken Erwin years to fog the few trees he fogged and sort the insects that fell down. Even from those samples, he had focused on only the beetles and even then, only some of the beetles. The rest lay in jars and piles. His estimate exists, to this date, in a kind of netherworld between what is known and possible.
What Terry Erwin really needed to do was to find and name all of the species in a single tropical forest, and then all of the species on which they depended for food. Knowing all such species for a given place would give Erwin a better estimate of host specificity and allow him to do better math. Erwin was at heart a beetle man. Narrower still, he was a carabid man. He had not sought anything grand and was not really that interested in studying species other than carabid beetles. He had made his offering to the debate on the number of species on Earth. Now, for a while anyway, he would turn back to the beetles. He would name the beetles that fell from that first tree. Each night before he fell asleep, he would look at a specimen or two under the microscope not far from his bed. Perhaps he knew how many species there were on Earth, and perhaps not—but either way, the ones he had collected had to be named. Either way, he needed to get to work. Like Leeuwenhoek, Erwin always returned to his microscope. Also like Leeuwenhoek, Erwin needed validation. He could not rest well while the question was unresolved. Over the years, he came back to it constantly.
Meanwhile, what were needed more than anything were more data. Sir Robert May, in a long article that followed Erwin’s on estimating global diversity, suggested that the next step might be to “assemble a team of taxonomists, with a comprehensive range of expertise, and then make a rough list of all the species found in one representative hectare in the tropical rain forest; it would be better to census several such sites.” He would go on to say that “until this is done, I will not trust any estimate of the global total of species.”21