from another, as well as the fact that morphology itself could be subdivided. For example, skin is an irreducible or “uniform” part of an animal, whereas a foot is composed of skin and several other parts, like muscle and bone. A close observer of animal behavior and anatomy, Aristotle also recognized a parallel principle of organization, in which similar species could be grouped into assemblages called “genera.” Aristotle’s definition of a genus was broad. Birds and fishes are examples of Aristotelian genera, and Aristotle regarded all terrestrial quadrupeds as belonging to a single genus. But despite their many important shared characteristics there are also unmistakable differences between, say, a lion and a porcupine. This led Aristotle to insist on the supremacy of species as the fundamental unit of natural history. “[W]e must take animals species by species and discuss their peculiarities severally.” And so it has ever been.
Linnaeus also emphasized the species as the fundamental unit of life. His binomial system was intended to make it easier to keep track of plant and animal taxa—whose numbers were expanding as European explorers pushed into new places across the globe. For several decades following the publication of Systema Naturae, students and colleagues sent Linnaeus specimens, mainly plants, from all over the world. He named them based on what he saw as their intrinsic qualities, like rocks whose origins could be explored with a hammer. Linnaeus believed the identity of a species was inherent in its appearance and that he didn’t so much choose a name as diagnose one. “The thing is, that each Stone, Plant, Animal itself shall tell the ignorant its own name so that it will be understood by everyone who has learnt the language,” Linnaeus said.
Linnaeus never imagined how truly extensive this language was. Late in life he realized that there were probably so many plants in the world that it would be hard to name them all. But he believed the number of species on earth was not incomprehensible. He estimated the total at 40,000. About half that number would be plants, with the next largest group being approximately 12,000 insects. Linnaeus thought there were maybe 2,000 species of birds and perhaps 200 mammals. He was low.
It’s a testament to the diversity and abundance of life that although we know Linnaeus was off in his estimate of how many species there are, nobody today really knows how far off. There are something like 1.7 million named species. But that’s only a small fraction of what’s out there. New species are discovered continually, and we’re not going to get a handle on the total anytime soon. Current guesses put the number at anywhere from 8 million to as many as 100 million, with 30 million being a generally accepted estimate. That includes a lot of bacteria, but also 4,300 mammals and nearly 10,000 birds. Linnaeus rightly suspected that there are many species of insects, though his estimate of 12,000 is amusing in retrospect. Beetles alone make up 300,000 known species. About one out of every three living things on the planet is a bug, and thousands of insect species thrive in anonymity in tropical forests.
Just as there were many more species than Linnaeus imagined, there was a need for more genera than he created to manage them all. As new species turned up in far-flung parts of the world like America, they were made to fit into a preexisting taxonomical scheme that seemed increasingly artificial. Linnaean taxonomy relied on morphology rather than behavioral traits or reproductive compatibility—features of natural history that required study in the field. This created confusion when unrelated species with a few coincidental similarities in appearance were crowded into the same genus. But this was only one of the shortcomings of the Linnaean system.
In Linnaeus’s day, the idea that species were the “words” of the language of biology was widely shared. Naturalists thought of nature as a book. And since nature was the product of divine Creation, this book was a kind of scripture. The study of nature was thus a pious attempt to read God’s book of life. But this raised a difficult issue. If the book of nature was a bible, then it was not meant to be edited. God was presumed to have created all living things at the same time and in a state of harmony that was immutable. Simply put, the plants and animals in the world were fixed. They were all of life that ever was or ever would be. The book of nature was written in indelible ink.
For most of his life Linnaeus believed this was so. “We count so many species as there were in the beginning,” he wrote in Systema Naturae. But he gradually came to the conclusion that at least some species arose over time. Linnaeus was sure these processes were so slow that nature could be regarded as essentially stable. Like many of his contemporaries, Linnaeus was groping his way toward a concept—evolution—that would not be articulated for another century. He didn’t get there because he didn’t realize that, just as new species could develop, the reverse was also true, and even God’s creations sometimes passed out of existence. Linnaeus had no concept of extinction.
To be fair, the evidence for extinction was still thin. Fossils—the gateway to former life forms—had long been seen as natural curiosities. But, as clues to the past, their meaning was murky. The presence of plant and animal shapes found in solid rock, and especially the appearance of fossilized marine life on mountaintops around the world, had puzzled people for centuries. There were imaginative explanations—though not to the point of guessing the truth—that whole worlds of living organisms had come and gone in the eons before us. It was believed by some that ocean life—possibly seeds or spawn—had been carried up to the mountains during the biblical deluge. Speculation during the Middle Ages centered on some kind of geological hoax perpetrated within the earth’s mantle, where supposed “plastic forces” created rocky simulations of living things. Earlier, the Greeks had thought it possible that the sea had once covered the land where marine fossils turned up. Aristotle believed such fossils might be the residue of creatures trapped in crevices of formerly submerged rocks. Leonardo da Vinci thought the fossilized assemblages of corals and shells found in the mountains of Italy argued against a biblical interpretation. He noticed they were intact and arranged in the same way as in the ocean. Da Vinci concluded that it was impossible for such objects to have been transported to the mountains in a pristine condition—especially by way of a violent, forty-day flood. Linnaeus took a pragmatic view of fossils, naming them as if they were any other extant species.
All of this would have to be rethought, and soon, because people had begun finding large, unusual-looking bones on both sides of the Atlantic. The discoveries in America were particularly important because they pointed up the shortcomings of Linnaean taxonomy, and also because they sharpened the dispute between American naturalists and another European authority, the great French scientist and nature writer Georges-Louis Leclerc, comte de Buffon.
Count Buffon—or just Buffon, as he was usually called—was a contemporary of Linnaeus. Born in 1707 to a middle-class family in the small town of Montbard in Burgundy, Buffon was an unremarkable student. But he had a curious mind and was fascinated by mathematics and science—as well as money, power, fancy clothes, and beautiful women. Drawing on reserves of ego, ambition, and literary ability, Buffon launched an unlikely but meteoric career as a celebrity naturalist. In 1739, King Louis XV of France appointed Buffon keeper of the Royal Botanical Garden, a prestigious, essentially administrative position. The “garden” was much more than a royal arboretum. It was actually a well-organized academy that offered coursework in medicine and natural science, and which had a small faculty as well as many specimens of plants and animals from around the world. Buffon devoted himself to expanding and cataloguing the collection, called the King’s Cabinet of Natural History. This work morphed into one of the most important and all-encompassing scientific publications of the eighteenth century, the Histoire naturelle, générale et particulière, avec la description du Cabinet du roi—Buffon’s Natural History. The first three installments of this encyclopedic undertaking appeared in 1749. By the time of his death in 1788, Buffon had completed thirty-six volumes, including an edition illustrated with copper engravings of mammals from every corner of the world.
The subject of Buffon’s Natural History was everything. Buffon endeavored to explain all that was known about the physical world, including its origins. He covered geology and anthropology, the formation of the planets, reproduction, astronomy, meteorology, mineralogy. He wrote about the oceans and air and continents. He covered physics and botany and zoology and, of course, taxonomy. Buffon liked naming things every bit as much as Linnaeus did, though the two profoundly disagreed on how to catalogue the taxa. Buffon thought the Linnaean system was flawed and far too generous