A Natural History of the Future

CHAPTER 1

Blindsided by Life

THE FIRST SPECIES OF HUMAN, HOMO HABILIS, EVOLVED ROUGHLY 2.3 million years ago. Homo habilis then begat Homo erectus. Homo erectus, in turn, begat a dozen or so other human species, including, eventually, Neanderthals, Denisovans, and Homo sapiens. All of this transpired over years during which many mammal species were very numerous. Reindeer numbered in the millions. Some mammoth species numbered in the hundreds of thousands. Yet the largest population ever attained by any human species between 2.5 million years ago and 50,000 years ago would have been around ten to twenty thousand individuals. These individuals would have been organized into highly dispersed, relatively small groups. At no time and nowhere did they abound. For essentially the entirety of prehistory, humans were relatively rare, their survival far from inevitable. That would change.

Around fourteen thousand years ago, our species, Homo sapiens, began to settle into more sedentary lives. For some populations, hunting and gathering gave way to farming, beer brewing, and baking. This transition brought population growth, which continued over the succeeding millennia. Roughly nine thousand years ago, as the first small cities began to emerge, the total number of humans on Earth was still relatively small, and yet the rate of human population growth had begun to increase. By the year zero, the total population on Earth may have been ten million, which is to say, the size of a modern Chinese city of no special renown. Yet, the rate of human population growth was continuing to increase.

Then, between the year zero and today, that rate accelerated. Earth added eight billion people. This increase in human populations has been called “the great escalation” or the “great acceleration.” The consequences of humans escalated, and the rate at which those consequences increased, year by year, accelerated.1

In the laboratory, we see the kind of population growth that humans underwent during the great acceleration when we study bacteria and yeasts. A few small settlement-like colonies on a Petri dish, when given as much food as they want and need, initially grow slowly, but growth accelerates until the food is devoured and the Petri dish is covered with bubbling life. We are that bubbling life on Earth’s Petri dish, a reality that began to be noticed as early as 1778 when the French naturalist, Georges-Louis Leclerc, the comte de Buffon, wrote, “The entire face of the Earth bears the imprint of human power.”2

During the great acceleration, the proportion of Earth’s biomass consumed by humans increased exponentially until, today, more than half of all the green growth on Earth, the terrestrial primary productivity, is consumed by humans. By one estimate, 32 percent of the terrestrial vertebrate biomass on Earth is now composed of nothing more than fleshy, human bodies. Domestic animals make up 65 percent. Just 3 percent is left over for the rest of vertebrate life, the remaining tens of thousands of boney animal species. Unsurprisingly in this context, rates of extinction have increased more than a hundredfold, perhaps much more. Any measure of the human effect on life over the last twelve thousand years shows a line rising, often exponentially. It is true of the pollutants produced by human societies. Methane emissions have increased by 150 percent. Nitrous oxide emissions have increased by 63 percent. Carbon dioxide emissions have nearly doubled to levels last seen three million years ago. The trends are similar for pesticides, fungicides, and herbicides. These effects are all increasing, all accelerating in step with the growth of our populations, needs, and desires.

At some hard-to-define point during the great acceleration, the populations and actions of humans ushered in a new geological epoch, the Anthropocene. It all happened so quickly. Compared to the long history of life, the growth of human populations was instantaneous. A train crash. An explosion. A mushroom rising from the wet ground of our origin. In confronting the consequences of this rise, as if studying the aftermath of a collision, one gathers the pieces and imagines that if enough pieces, enough details, are gathered, the whole will make sense. This seems to be a logical supposition, so logical that it has become a common approach to doing science. For biologists, the pieces that are gathered are species. Biologists examine the species. Biologists chart their details and their needs. But there is a problem with this approach: our own lack of awareness.

The species we study to understand the world are nearly all unusual species. They are species that are representative neither of the realities of the living world nor of the portion of the living world most likely to affect our own well-being. Our problem is simple. We tend to assume the living world to be both like us and relatively well understood. Both of these assumptions are wrong, the result of law-like biases in the way we make sense of the world. I begin by considering these biases because we can’t understand the natural history of the future without being aware of the wide gulf between our perceptions of the biological world and its more interesting realities.

The first of our biases is anthropocentrism. This bias is so deeply part of our senses and psyche that it might be called a law, the law of anthropocentrism. The law of anthropocentrism is grounded in our biology. Every animal species has a perception of the world framed by its own senses. If it were dogs that were in charge of science, I’d be writing about the problem of caninecentrism. But what is unique with humans is that our bias influences not only the way we individually perceive the living world around us, but also the scientific system we have built to catalog the world. It was the Swedish natural historian Carl Linnæus who gave our system its rules, but he also gave the system’s anthropocentrism momentum, inertia, and a peculiar geography.

Linnæus was born in 1707 in the village of Råshult, about 150 kilometers northeast of the city of Malmö in southern Sweden. Råshult has a climate more or less like that of Copenhagen, Denmark. It has some of the coldest summers in the world, and its winters are sufficiently dark and cloudy that when the sun appears, people turn their faces to it like sunflowers. They even point. “There it is!” It was in Råshult that Linnæus became interested in nature; it was farther north in Sweden, in Uppsala and its surrounds, that he would study nature.

Sweden, despite its large size, is among the least biologically diverse countries in the world. Yet Linnæus assumed that the biological poverty of his home place was the norm. Linnæus’s trips outside Sweden were to the Netherlands, northern France, northern Germany, and England. These regions are slightly more southerly than Sweden, and yet, relatively speaking, they are much the same in terms of their biology. As seen and imagined by Linnæus, Earth’s landscape was, if not uniformly Swedish, at least Swede-ish. It was rainy and cold and populated by deer, mosquitoes, and biting flies and by beech, oak, aspen, willow, and birch trees. It was a landscape of delicate spring flowers, late summer berries, and fungi pressing up out of the ground in the wet fall, just in time to be eaten.

Before the 1700s, scientists in different places and cultures had different systems for naming life. Linnæus codified and began to implement a universal system, a scientific common tongue, in which each species was given a genus name and a species name in Latin; humans, for example, would be Homo (our genus) sapiens (our species). He then considered the species near at hand. He studied and touched them, bestowing on them, as if in blessing, new names—Linnaean names.

Because Linnæus began renaming species in Sweden, the first species he renamed were Swedish and, more generally, northern European. The Western scientific tradition of naming all of life began with a Swedish bias. Even today, the farther you go from Sweden, the easier it is to discover a species new to science. Nor was Linnæus’s Swedishness his only bias. He was also inescapably human. It couldn’t have been otherwise. As a human, Linnæus tended to study the species around him that visually commanded his attention. Linnæus liked plants and had a particular fascination with their sex parts. But he also studied animals. Within the animal kingdom, vertebrates received most of his focus. Among the vertebrates, Linnæus tended to pay attention to mammals. Within mammals, Linnæus tended to ignore small species, such as the innumerable kinds of mice, preferring to feature bigger species. In general, his focus was either on species that were visually pleasing or obvious to him and to his colleagues, such as flowering plants, or on species that were enough like us in size or behavior to be both easily seen and relatable. In this way, his focus was both Eurocentric and anthropocentric. The scientists that Linnæus trained, and modestly called his “apostles,” for the most part followed in his footsteps and had similar biases. So too have most scientists since. These biases influence not only which species are named first,3 but also which species are studied in detail and especially which species are the subject of conservation efforts.

Figure 1.2. The number of vascular plant species in each of 103 different countries. Note that Sweden is among the least biologically diverse countries with regard to plant diversity. For example, although Colombia is just twice as big as Sweden, it contains roughly twenty times as many plant species as does Sweden. Patterns in the diversity of, for example, birds, mammals, and insects are similar.

The problem with the Eurocentric and anthropocentric biases of science are that they give us a false impression of the world. They lead us to imagine that the species we have studied are a reflection of the world itself, rather than just the part of the world we have chosen to study. Several decades ago, it became clear just how wrong this perception was when scientists started to consider a simple question: “How many species are there on Earth?”

Attempts to answer this question in earnest began with the entomologist Terry Erwin. In the 1970s, Erwin set out to study a group of beetles that live in the tops of tropical rain forest trees in Panama. These tree-living beetles, which most often live at the interface between branches and clouds, are called ground beetles because they were first studied in Europe. In Europe, ground beetles are not terribly diverse, but the species that are present do, indeed, tend to run around on the ground.

In trying to find and identify ground beetles in the sky, Erwin deployed a new method. He would climb up into a tall tree, using ropes, and then spray a fog of pesticide into the canopy of an adjacent tree. Initially, he fogged trees of the species Luehea seemannii. After fogging trees, he returned to the ground and then waited for dead insects to fall. When Erwin tried this method for the first time, the insects fell by the tens of thousands onto tarps that he had stretched out on the forest floor. To his delight, there were ground beetles, but there was also a great deal more.

Erwin would ultimately tally about 950 species of beetles in Luehea seemannii trees, at least for the kinds of beetles that he and his collaborators could identify. On top of that, he estimated there were an additional 206 species of beetles in his samples from the weevil family, though no weevil expert had time to formally make the necessary identifications. The resulting total of about 1,200 species of beetles amounts to more beetle species in one kind of tree in one forest than there are bird species in the United States. Erwin next considered other kinds of insects and then other kinds of arthropods more generally. He came to notice that not only were most of the species of ground beetles new to science, but so too were most of the species of other kinds of beetles and most of the species of each and every other kind of arthropod. What was more, when Erwin started sampling other kinds of trees, he saw different species than he had on the Luehea seemannii trees. Each rain forest tree species had its own insect and other arthropod species, and tropical rain forest tree species are extraordinarily diverse.

Erwin was confronted with a riot of unnamed life. He was surrounded by species no scientist had ever seen before, much less studied in any detail. No one knew anything about these species, other than the trees from which they had fallen. It was at this point that Erwin received a call from the botanist Peter Raven. Raven, then director of the Missouri Botanical Garden, asked Erwin a simple question. If there were so many unnamed beetle species in a single tree of a single species, “how many species might there be in an entire acre of forest in Panama?” Raven’s question was prompted by work he was doing as chair of a National Research Council committee charged with identifying the gaps in our understanding of tropical forest biology.4 Erwin responded, “Peter, nobody knows that stuff about insects. It’s just impossible.”5

At the time Raven called Erwin, there was no good estimate of the diversity of life on Earth. In 1833, the entomologist John Obadiah Westwood polled his entomological acquaintances and, on the basis of the results, hypothesized that there might be five hundred thousand insect species on Earth, to say nothing of other kinds of organisms. In the context of his report to the National Science Foundation, Raven had also offered an estimate, based on some simple math. He predicted there might be three to four million species on Earth. If Raven was right, more than half of all species on Earth were unnamed.

Meanwhile, although Erwin had said it was “impossible” to estimate the number of species of insects in an acre of forest in Panama, much less the number of all species on Earth, he decided to give it a try. He started by doing some calculations. If there were 1,200 species of beetle in the Luehea seemannii trees, and one-fifth of those beetle species were dependent on that particular tree species, how many beetle species might there be in a hectare of Panamanian forest? Assuming that the discoveries he had made in Luehea seemannii trees were representative of the sort of specialization he might find on other tropical trees, Erwin calculated the number of beetle species in a Panamanian forest, given the number of tree species present. He then adjusted his figures to get an estimate of the total number of arthropods (encompassing not just insects, but also spiders, centipedes, and the like) more generally. The result was forty-six thousand species of arthropods in a hectare of forest in Panama. That was his answer for Raven (though it was a little late—Raven’s report to the National Science Foundation had, by then, been long since published). But Erwin decided to go a little further. He used the same sort of simple math to estimate the number of arthropod species not just in a hectare of forest in Panama or all the forests in Panama but, instead, in all the tropical forests of the world. If there were about fifty thousand tropical tree species on Earth, Erwin wrote in a two-page paper in the Coleopterists Bulletin, “there might be 30 million tropical arthropod species in the world.” Given that only about a million species of arthropods (and 1.5 million species of organisms more generally) were named at the time, this would mean that nineteen out of every twenty species of arthropods were not yet named!6

Erwin’s estimate provoked a wave of academic controversy. Scientists debated its validity aggressively in print and passive-aggressively in person.

Some scientists suggested, in private, that Erwin was foolish. Some said it in public. Some thought him foolish because his estimate was too high. Others thought he was foolish because his estimates for their own favorite groups of organisms were too low. Dozens of scientific papers were written. Erwin wrote responses to the responses to his papers. He collected new data. He wrote more papers, which, in turn, triggered new responses. Meanwhile, other scientists were inspired to collect new data. More papers were written. The work of refining, rejecting, or improving Erwin’s estimate was aggressive, furious, contested, and public.

Eventually, the debate basically ceased, or at least slowed dramatically. After years of debate, scientists had reached a kind of quiet consensus; the number of unnamed species of animals was sufficiently large that it would be centuries before we know for sure whether Erwin was right. The most recent estimate of the number of insect and other arthropod species on Earth suggested there might be about eight million, which is to say that seven out of eight animal species are not yet named. Eight million is fewer species than Erwin hypothesized and yet still far more than had ever been imagined before his work.7 The unknown is large; the known is humble.

In causing scientists to reconsider the dimensions of animal life, Erwin served as a kind of Copernicus of biodiversity. The astronomer Copernicus argued that the universe was heliocentric. Earth, Copernicus said, circled the sun rather than the other way around, and in addition, Earth rotated on its axis once a day. Erwin, meanwhile, revealed us to be just one animal species among millions. He also revealed that the average animal species is not a vertebrate like us, or northern (like Linnæus). It is instead a tropical beetle, moth, wasp, or fly. Erwin’s insights were radical. Indeed, they were so radical that it has proven more difficult to incorporate them into our daily understanding of the world than it was to imagine that still-seeming Earth is both spinning on its axis and circling the sun.

The Erwinian revolution in our perspective does not end with insects. Fungi, such as those that produce mushrooms, appear to be even more poorly known than are insects. My colleagues and I recently studied the fungi found inside houses across North America. We found fungi in every house. But what was remarkable was not the presence of fungi but, instead, the number of kinds of fungi. The most recent tallies of all the named fungi in North America noted roughly twenty thousand species. By studying the dust in houses, we found twice as many species.8 That is to say that no fewer than half of those species we found in houses must be new to science—thousands of fungus species new to science in homes. It isn’t that houses are special. Instead, the teeming, unnamed, fungal multitudes in our own homes simply point to our broader ignorance of the fungal life around us. Each time you breathe in, half of the kinds of fungal spores you inhale are yet to be named, much less studied in sufficient detail to understand their consequences for our own health and well-being. Pause now to take a breath; inhale the fungal unknown. Fungi are probably not as diverse as insects, but they are far more diverse than are vertebrates.

But it isn’t the fungi that we must make sense of if we are to complete the Erwinian revolution; it is, instead, the bacteria. Linnæus knew of the existence of bacteria, but he ignored them. He lumped all microscopic life into what was, in effect, a single species, “chaos,” too small and different to be organized or even organizable. Recently Kenneth Locey and one of my collaborators, Jay Lennon, tried to take the measure of this chaos. They focused just on bacteria and estimated that there might be a trillion kinds of bacteria on Earth. A trillion (1,000,000,000,000).9 A trillion. Perhaps it was these multitudes that Terry Erwin had in mind when, later in his career, in a moment of humility before the grandeur, he noted that “biodiversity is infinite” and “there is no way to estimate the infinite.”10 Locey and Lennon’s assessment of bacterial diversity was not that it is infinite, but relative to the known world, it is nearly so. Locey and Lennon based their estimate on the study of data from thirty-five thousand samples, from around the world, of soil, water, feces, leaves, foods, and other habitats in which bacteria dwell. In those samples, they were able to identify five million genetically different kinds of bacteria. They then used some of the general rules of life (for example, how the number of species in a habitat increases with the number of individuals in that habitat) to estimate how many kinds of bacteria they would have encountered were Earth to be sampled completely. The answer was a trillion, give or take a few billion. Locey and Lennon’s estimate may well be very wrong, but it will be decades, maybe centuries, maybe longer, before we can say for sure. In a casual, drifty, late-day conversation, one of my close colleagues said she thought there were probably only a billion species of bacteria. But then she went on to say, “However, I have no idea. What I do know is that new bacteria species are everywhere.” We are sitting on them, breathing them in, and drinking them; we are just not naming or counting them, or at least naming or counting them remotely fast enough to make sense of the wilderness we walk through each day.

By the time I was a graduate student, Erwin’s estimate had led scientists to imagine that most species were insects. For a while, it seemed as though fungi might be the big story. Now it seems as though, to a first approximation, every species on Earth is a bacterial species. Our perception of the world keeps changing; more specifically, our measure of the dimensions of the biological world keeps expanding. And as it does, the average way of living in the world seems to be less and less like our own. The average animal species is not European, nor is it a vertebrate. And as for the average species more generally, it is neither animal nor vegetable; it is instead bacterial.

Bacteria, though, are not even the end of the story. Most individual strains and species of bacteria appear to have their own specialized viruses called bacteriophages. In some cases, as bacteriophage expert Brittany Leigh reminded me recently via email when reviewing this chapter, the number of kinds of bacteriophages outnumbers the number of kinds of bacteria ten to one. If there are a trillion species of bacteria, then it is possible there are also a trillion kinds of bacteriophages or even ten trillion kinds of bacteriophages. No one knows. What we do know, with certainty, is that the vast majority of species are not yet named or studied in any way or understood.

Beyond the bacteriophages, there is a final layer to this unraveling of our position at the center of things. It may be that the average species is not only not European, and not an animal, but also, not able to survive on the surface of the Earth, as I was recently reminded by Karen Lloyd, a microbiologist at the University of Tennessee.

Lloyd studies microbes that live beneath the ocean in Earth’s crust. Not long ago, it was thought that Earth’s crust was devoid of life. Research by Lloyd and others has shown, instead, that it is brimming with it. The organisms living in the crust do not depend on the sun for sustenance. They rely instead on energy generated by using gradients in chemicals deep down below us all. They use such energy in order to live simple, slothful lives.

Some of these organisms live so slowly that a single generation might take from a thousand to ten million years. Imagine, now, one cell of one of those latter, ten-million-year species. Imagine a cell that is about to divide, finally, tomorrow. It might have last divided before the ancestors of humans and gorillas began their separate trajectories. It would have last divided even before the ancestor of chimpanzees and humans diverged from the ancestor of gorillas. In one generation, such a cell would have lived through not only the entire sweeping evolutionary story of humans, but also all of the great acceleration. What will the next generation in that lineage experience in its lifetime, one that could conceivably end in about the year ten million?

These slow-living, chemical-eating crust microbes were discovered only relatively recently. But they are now thought to represent up to 20 percent of all of the living mass of life (what scientists call biomass) on Earth. Depending on how deep they go, this may be an underestimate. We have no idea how deep they go. Deeper, certainly, than we humans have been. The crust microbes aren’t “normal.” Theirs is not the average condition of life. Yet their lifestyle is actually more common, whether measured in terms of biomass or of diversity, than is the mammalian lifestyle or the vertebrate lifestyle.

The average species is neither like us nor dependent on us, in contrast to what our anthropocentrism would tend to suggest. This is the key insight of the Erwinian revolution that goes along with the recognition of what I call Erwin’s law. Erwin’s law states that life tends to be far less well studied than we imagine it to be. Together, the law of anthropocentrism and Erwin’s law are hard to remember in our daily lives. It might require a kind of daily affirmation. “I am large in a world of small species. I am multicellular in a world of single-celled species. I have bones in a world of boneless species. I am named in a world of nameless species. Most of what is knowable is not yet known.”

It is surprising that we as a species have been as successful as we have despite our ignorance of the biological world and our biased perspective on its dimensions. Einstein said that “the eternal mystery of the world is its comprehensibility”; in other words, what is incomprehensible is how much we comprehend.11 But I don’t think that is quite right. I think that what is even more incomprehensible is that we have survived despite how little we have comprehended. We are like a driver who somehow gets down the road, despite being too short to see out the window, a little drunk, and very fond of acceleration.