We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time.
T. S. ELIOT, “LITTLE GIDDING”
When my wife and I were newly together, we took a trip to Costa Rica. We had been working in separate parts of the country and met up at the end of our duties to travel. We decided to take a several-day hike in the rain forests of Corcovado National Park. Predictably, we hiked a little too slowly. We were talking and not paying enough attention. I was probably looking for cool bugs. She was probably wondering if the snake I had absentmindedly stepped over was poisonous. Night was beginning to fall, and as the moon came up between some high trees and we began to wonder where we might sleep, we happened into an apparently abandoned orchard. There were sweet fruits whose names I have never discovered, and aromatic vines that dangled over the fruit. Just as in Bolivia, we again indulged and were simply delighted with the moment, so delighted that for a long while we did not worry about the night. We just kept walking through that orchard, exploring, finding new fruits, eating, and laughing. For those moments we were so happy that the idea that the orchard could ever end was almost unbelievable.
Anatomically modern humans first appeared in Africa around two hundred thousand years ago. For most of subsequent human history, we lived in a world defined, as our moment was in the orchard, by our immediate surroundings. We knew the visible species around us, particularly those that were deadly or delicious. Sometimes we stumbled upon a new fruit and tried it. What did not kill us probably led us to eat a little more.
In the last three hundred years, the Western view of the world has changed in many ways. The big discovery, the discovery that this book encapsulates, is that life is more diverse and less like us than we had imagined. This discovery might be called Leeuwenhoek’s revolution. Copernicus banished man to the edge of the universe. A few centuries of biological discovery have pushed us to the edge of life. The rest of life does not revolve around us, nor is it like us.
Yet, in our daily lives we remain central. The astrobiologists, when they get together, talk not about the universe but about each other. We cannot, without repeated reminders to wake up and pay attention, live any other way. Most days you do not look at the stars, and in the same vein it is all too easy to ignore the other life we pass by. The species on our bodies are small, and the crust of the Earth is so far away.
Because we focus on just those species like us and around us, it makes it easy to imagine we are close to finding every domain of life, or even every species. There is nowhere to hide a new monkey, the logic goes, and so ever since we began to name those species in the communities beyond our own, we began to believe ourselves close to finding everything. Yet every time we have come close to knowing all the species or even all the kinds of life, some new realm has been discovered. Ironically, discovering so much more about our biological world seems only to affirm our own ignorance. The discoveries will continue, I suspect, unabated. As Carl Woese said in a recent interview, “the depths of biology have yet to be plumbed.”1
From an evolutionary perspective, the idea that we have not yet figured everything out should not be so surprising.* As the tree of life gets bigger and our place in that tree gets smaller, the tree becomes filled with more species, each of them building a simple vision of what the world looks like. Biologists like to map the traits of species onto evolution’s trees. Perhaps now we could map some measure of the awareness each species has of its world. The microbes would understand gradients, measures of the concentrations of nutrients, light and dark. The plants, too, respond to such gradients. They sense each other, feel herbivores on their leaves and fungi on their roots, and measure the sun. The insects check the interstices, the holes and small things we miss. They see the quick movement in the litter. Their world is smaller than our world, more representative of the average way that Earth is experienced. Then there are the vertebrates, whose view of the world comes nearer to ours. Closest to us we have the chimpanzees, or more generally the great apes. Their view of the world is simpler than ours (no atoms or quarks, no black holes or planetary orbits), but still relatively complex. It would be tempting to look at the chimpanzees and laugh a bit at how little of the world they do understand, but it is also worth remembering the years that separate us. We were, a million years ago, not yet human and not yet uttering words. A few hundred years ago, the sun still revolved around the Earth. We have, in just a few hundred of the four billion years of life on Earth, derived our entire understanding of the world. We seem to expect too much: to understand everything today, to be as knowledgeable now as one could ever be.
I am not arguing that we should slow down our search to know everything. I am simply arguing that we ought to be more humble in that endeavor. We ought to leave enough room for awe at what is still possible. After all, a great deal is still possible and will yet be discovered. There are questions we will not answer for a thousand years. There are probably questions we may never answer.
As scientists, we are perpetually willing to shine our lights around us, see nothing, and conclude that there is nothing left to see. Our lights are weak, the universe large. Look out just beyond what we know and you will see some movement, some sign of something else just beyond what is visible. Just what is out there, I cannot tell, but I am sure as hell swinging my light, looking and smiling at the raw possibility of what might leap out and catch us by surprise.
We have many questions yet to resolve: When, and how many times, did life evolve on Earth? Did life first evolve on Earth? Has it evolved elsewhere? What are the hottest, coldest, or most extreme conditions where life can live? Is there life in the magma at the center of the Earth (or even: Is there magma at the center of the Earth)? What are the smallest species? Is there a limit to how big species can be? Can life evolve without DNA? Does such life already exist on Earth? Do bacteria make oil and coal? Which kinds of species (bacteria, archaea, vertebrates, plants?) represent the majority of the weight of life on Earth? Do the species on Earth account for all of life in the universe? Is Earth just one of a million planets with life? Do species disperse from Earth to other planets?
Not one of these questions is ridiculous, and not one of them is even close to being answered. We just do not know. Furthermore, the biggest discoveries usually seem to result from answering questions we do not yet know are interesting. We cannot even see well what we need to ask. We are still in an orchard of species in which we wander about discovering things. We still see only as far as our lamps, our tools, our means of extending our humble senses, allow us to see. The rest is dark and full of possibility, full of sounds we cannot yet decipher and movement we do not yet understand. In the end, what differentiates us from Juan, the indigenous man in the middle of a Bolivian forest who looked at me and asked if we, too, have a moon, is just that he knew it was not outrageous to ask.
In age, Linnaeus began to suffer from what may have been dementia. He imagined he was in the field. He imagined he had gone with his student-apostles to the far reaches of the globe. Even in his lucid moments, he looked around to find a world he had named, but a world for which the names had begun to escape him. What was the name of the man standing in the foyer? Of his wife? Of the plants around him?
The world had lost its nouns. The man who had once hoped to name everything could not always remember the word “desk,” or “table.” He could not always recognize the people who cared for him, moving him from room to room, bringing his food, tending to him. It was, for a time, like that first landscape he found as he traveled north. He was once again in a nameless world that he could take control of by force. It is hard to imagine that this condition greeted him with anything but horror.
All men die. It is a trite observation. But it is somehow especially humbling to see the men and women who lived by intellect fall to the very organicness of their bodies. The minds that hold back the dark ages, that keep us pressing into the night, do in time wilt.
When Leeuwenhoek died, no one would continue his work for a hundred years, and even then, not with his fervor. The scientists in this book all, to a one, die as obsessed with their work as they have ever been. They do not retire. They do not move to Florida or “tone things down.” One of the few options available to these discoverers is persistence. They have seen our greatness, but more important, they have seen our ignorance. They have seen the breadth and depth of what can still be discovered and know that with just the right wind, the ships of their intellects can take off again, cruise across the lake of unknown things, and discover once more something big, real, and new.
When discoverers age, the ends of their lives are as varied as their beginnings, but there are some universal themes in their stories that-might allow us to predict something for the still living discoverers. In their last days, the discoverers still gripped podiums. They still looked out at crowds and they still, to a one, espoused things their peers believed to be deeply wrong.2 Scientists who make big discoveries must, at some point in persevering with their bold ideas, come to the opinion that everyone else is wrong. To persist, Lynn Margulis, Carl Woese, Antonie Leeuwenhoek, and others had to believe that they were among the only individuals in the world who understood. Once a scientist believes so strongly in her own opinions and is proven right, it becomes easy to believe again. It becomes easy to believe that the brilliance or madness that she possesses is the truth. Science’s filters, its checks and balances, can lose their cachet. Thoreau wrote, “If a man does not keep pace with his companions, perhaps it is because he hears a different drummer. Let him step to the music which he hears, however measured or far away.”3 It is easy enough, after discovery, for scientists to find themselves out of pace with their companions, dancing to some other drummer and far away from daily life. Minds flexible enough to make big discoveries can also turn a little gullible.
Maybe greatness occasionally, or even often, requires a kind of suspension of the irritable skepticism at science’s core. Linnaeus died believing that mermaids were the missing link between humans and other species, and that he might still find one. He believed that swallows over-wintered underwater rather than migrating. Carl Sagan died believing in gentle and intelligent life in nearby solar systems. Lynn Margulis believes that the tails of sperm are, or were, separate organisms, that the Earth is a self-balancing system, and more. Carl Woese looks into deep history and thinks he sees the cell that is the mother of all life and, more recently, sees a new non-Darwinian model of evolution.4
Some of these ideas could be the muddled thoughts of aging scientists. They are easy enough to write off as unimportant. Alfred Russel Wallace codiscovered natural selection, is the undeniable father of biogeography, and yet spent much of his life attending séances.5 For Wallace, like many discoverers, much more remained possible than known.
It is easy to proclaim as wrong a new idea (or in the case of séances, a wild old idea). Skepticism and intellectual inertia keep science from disintegrating into madness. Natural selection withstood science’s skepticism, but séances did not. Our collective skepticism is clumsy and often begins by rejecting new ideas even if they are right. While we must be skeptical, it is worth remembering the possibility that we are all, except for one bold new scientist, wrong. Lynn Margulis may be right about the tails of sperm having a separate microbial origin. Carl Woese might be right about the origin of life. I, for one, having spent time with the ideas of these great minds, know better than to stand up and say that any of Lynn Margulis’s or Carl Woese’s wild ideas are foolish. For now, I’ll wait and see.
A recent example may shed light on the more general point. Perhaps more so than many recent discoverers, the ideas of Lynn Margulis have continued to draw fire. Some scientists seem to think that after discovering the role of symbiosis in evolution, Margulis should have smiled happily and returned to the daily activities of committee meetings and advising students. Instead, she said more and more wild things. Like Woese, she sees a new framework for understanding evolution.* She also imagines that bacterial species are nonexistent, and considers that there is a self-regulating biosphere, which she has called “the tough old bitch Gaia.”6 What most irks Margulis’s critics, however, is that she still clings to her idea, formulated when she was in her twenties, that flagella, cilia, and centrioles arose in cells by symbiosis. It is her tenacious appeal that every part of her original theory must be right, that this last piece of the puzzle will eventually fall into place (and therefore that she could not have been even a little wrong), that makes her seem, quite simply, stubborn.
When I began writing this book, everyone besides Margulis and a few of her collaborators seemed to have abandoned the idea of the symbiotic origin of centrioles, cilia, and flagella. There seemed to be a collective hope that Margulis too, would give it a rest. Then, improbably, a team led by Mark Alliegro, working out of Louisiana State University, isolated RNA from the centrioles in clams. The putative centriole RNA is very different from clam nuclear RNA and looks most like RNA from bacteria, as would be expected were the centrioles the result of endosymbiosis. The work is too new to be evaluated well, but suddenly it seems possible that even the part of Margulis’s theory that her supporters, for twenty years, doubted, may be right after all.7
We began with Linnaeus, so we will finish with him. As he aged, Linnaeus did not descend into more and more wild theories, but neither had he in life. He was a cataloger, not a theorist. There were always more things to add to the catalog. In the winter of 1778, his doctor advised his family that he was too ill to travel. Linnaeus was confined to his own home, where he paced when he was well enough. On one late evening, he instructed his driver to take him to his small cabin in the woods. The driver knew better, but also, perhaps, saw the dearness of the wishes of an old, sick man. He drove on in a small sleigh to the cabin, where Linnaeus sat, still in the sleigh, and began to smoke a pipe. Through the window, the stars opened before him. The moon rose over a land that he had named. He might not have remembered the names, but he knew they were his. Somewhere to the north was Andromeda, leaning her head to the ground.
Linnaeus’s family finally found him and brought him home. He died soon after, on January 10, 1778. He had suffered, by then, a lengthy period of deteriorating health and a series of strokes. In his final days he remembered little. He read his own words in book after book; he was not sure who had written them, but he was sure that they were the words of a brilliant man.
His funeral was somber and quiet. He was already famous, but less so in Sweden than elsewhere. His things were kept where they had been left, so that his son might use them. To be generous, his son was a reasonable sort of scientist, but he never understood or sought his father’s greatness.
There are still many species to put into Linnaeus’s cabinets. We will discover big, new things, to be sure, but before we do we must work on the smaller, older things, and the work left to do is stupefying. The kind of work proposed by Janzen and continued by Erwin is often thought of as a kind of stamp collecting. Find the species, name them, and put them in their evolutionary pigeonholes.
While the apostles risked their lives to find more species and fill the cabinets of life, Linnaeus paced the garden beside his house in Uppsala, puzzling over species and over his own legacy and grandness. He looked out across the world and saw, perhaps, ten thousand more species in the entire world, all of which he might name in his lifetime.
Since Linnaeus’s death more than forty thousand additional species have been named in Sweden alone. More than two million species have been named on Earth. Bacteria were finally understood as a distinct realm of life, as were archaea, viruses, and protists. The continents, it was learned, move, ferrying species about like so many passengers on an ark. Life exists on the bottom of the ocean, in the hottest corners of the Earth, on our bodies, in our bodies, and even in the air itself. Life could yet be found in space.
Linnaeus did not quite name everything. He would have admitted as much as he lay dying, but he did not know how much more would follow, just as we cannot know how much more will follow us.
Since Linnaeus, we have not become more humble. Every few years someone holds forth on the end of science or the end of discovery. I can’t rule out that those public criers are right. I do know, though, that if history has a lesson for science, it is that we are ignorant. The corollary, of course, is that those who say we have discovered everything tend to look the most ignorant.
Assuming that we know our world when we really do not has costs. We invest less in science than we should, for example. The biggest cost has to be that it leads young scientists to believe there is nothing left worth studying. In an age when getting children outdoors or into science seems more and more difficult, we are doing real harm if we do anything to dissuade our children from being curious and from believing that they can discover big and wonderful things. Science is full of egos and arrogance, but it is fuller of simple moments of pleasure at the joy of finding some gem of new knowledge, big or small. Such gems can be anyone’s.
Meanwhile, Linnaeus has risen from the grave with a message. Back in Uppsala, the Swedes are up to Linnaeus’s old tricks. Ulf Gardenfors, an entomologist in Uppsala, is leading an effort to at long last, and this is to be said aloud only meekly, name all of the species in Sweden (perhaps the least diverse nation on Earth). In Sweden, all of the multicellular species will be named by 2021. I can think of no more apt statement of how far we still have to go. In the country where Linnaeus, 250 years ago, was bent on naming everything in the world, we are only just now getting to name every multicellular Swedish thing.
The project has a reasonable budget and keeps plugging along. In interviews, Ulf has shown a whimper of the old hubris of Linnaeus, “we are on track to name every species,” but he must be humbled by his scope. He might also be humbled by Linnaeus’s own plight, the man who stood two hundred years earlier and claimed his stake of the world.
In considering the Swedish project, biologists from other regions are quick to offer support, but also context. Dan Janzen, upon hearing of the project, reminded a reporter that as many species could be found in the Guanacaste Reserve in Costa Rica, where he continues to toil, as in all of Sweden.8 Costa Rica on its own could hold a hundredfold more species than Sweden. Yet even the task of naming the Swedish species, so much more timid than what Linnaeus had envisioned for himself, will require more than a hundred taxonomists and thousands of amateurs. Amateurs go into their backyards and send in samples of flies, ants, bees, and wasps. Professionals categorize them. In one fly genus, Megalesia, there have been twenty new species discovered. Linnaeus must not have had enough room in his field bag.
No one in Sweden has said anything about describing all of the bacteria, archaea, viruses, protists, extinct life, or even, for that matter, distinct evolutionary units. It is not in the cards. It is too much. Maybe Ulf is right that we will fill in the last unknown species of multicellular creatures in Sweden in a few dozen years. Maybe we will then move on to the microbes. Maybe we will even someday name all the species of archaea, bacteria, and eukaryotes in the world.
But I doubt it.
Linnaeus saw the world as full, but not overburdened, with possibilities. It was a world that we could take dominion over. It was a world within our grasp. Leeuwenhoek, on the other hand, looked at the world through a single lens, and he saw through that lens a world perpetually just beyond his reach. He lived to be nearly a hundred and showed no signs of wearying of studying the things that lived within feet of his bedroom. He saw at the fuzzy edges of his lenses more things that might be seen, if only he looked a little more and a little harder. Linnaeus looked out to the edge of the Earth, to the horizon, and saw an edge. He would put his boat in and sail that far. Leeuwenhoek eyed that same horizon and saw something else. He saw at that fuzzy edge, or maybe he imagined, a glimmer of something farther. He put his boat out, but no matter how far he got, the horizon seemed to retreat, the unknown seemed always, for his entire life, despite all that he saw, as large as it had always been.