The Linnaean Enterprise: Past, Present, and Future 1

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1 The Linnaean Enterprise: Past, Present, and Future 1 EDWARD O. WILSON Pellegrino University Professor, Emeritus, Harvard University IT CAN BE reasonably assumed that the first words to emerge during the origin of human speech included the names of plants and animals. That advance, which probably occurred during the transition from Homo erectus to Homo sapiens a half million years ago, can be regarded as the earliest forerunner of science. Accuracy and repeatability in communication about the environment were then as now necessary for survival. Getting things by their right names, as the Chinese put it, is the first step to wisdom. During the past 2,300 years systematics, the science of classification, evolved in Western culture through four stages. The first was the hierarchical system introduced by Aristotle. Although this first systematics of recorded history muddled the picture somewhat by strict formal criteria based on Platonic essentialism, he did establish the concept of taxonomic hierarchy in this case the eidos of a particular form, such as horse, dog, or lion, and the genos, a combination of such forms that can be regarded as part of Earth s natural order. Aristotle recognized some 520 animal species, mostly from Greece, that were consistent with his definition of eidos. During the Middle Ages and into the Enlightenment, much of the research of early life scientists consisted of systematics in the Aristotelian mode, in an effort to perfect a system of classification for all known plants and animals. Microorganisms and the smallest multicellular organisms of course remained largely unknown until the invention of the microscope in the 1600s. The work of these authors, including Andrea Cesalpino, Caspar Bauhin, Joseph Pitton de Tournefort, and John Ray, culminated with the system devised during the mid-1700s by Carolus Linnaeus. 1 Read 22 April 2004, as part of the symposium Science, Art, and Knowledge: Practicing Natural History from the Enlightenment to the Twenty-first Century. PROCEEDINGS OF THE AMERICAN PHILOSOPHICAL SOCIETY VOL. 149, NO. 3, SEPTEMBER 2005 [ 344 ]

2 the linnaean enterprise 345 The great Swedish biologist, whose name is virtually synonymous with the modern era of systematics, made three decisively influential contributions. The first, presented in the Leiden Systema Naturae of 1735, formalized the hierarchical system of classification used today. A direct philosophical descendant of Aristotle s first scheme, it grouped all known organisms into three kingdoms, which were then divided successively downward into classes, orders, genera, and species. The basic unit Linnaeus recognized is the species, and he aggregated the higher taxonomic categories into successively larger clusters of species according to their anatomical similarity. Although Linnaeus believed in special creation, he nevertheless spent his entire career striving to define the diversity of life as a natural, comprehensible system as opposed to an arbitrary, chaotic system. Linnaeus s second major contribution was the binomial nomenclatural system, introduced in the Stockholm Systema Naturae in The early procedure he had used was that of the very capable Joseph Pitton de Tournefort, who in 1700 characterized each genus by a single term and the species within it by a brief diagnostic description. Linnaeus took the next step by simplifying the procedure with a single Latinized name for the genus coupled with a single Latinized name assigned to the species, followed by a diagnostic description. Thus we have today our own species Homo sapiens and our faithful companion species Canis familiaris. From this procedure was to grow the modern rule of nomenclatural priority observed by all taxonomists: in order to ensure stability, the first binomen applied to a species with a formally published description must thereafter prevail and exclude the use of other binomens. Another stabilizing rule that arose from this procedure is the designation of types, the specimens used in the original description and as a result designated as the final reference for the species and its binomen. Linnaeus s binomial system facilitated his third great contribution, the initiative to find and diagnose the entirety of biodiversity, from the local Swedish biotas to all those around the world. Such an effort became technically possible in Linnaeus s scheme because large numbers of species, including novelties, could be diagnosed and labeled efficiently. Linnaeus himself stayed mostly at home, with trips only as far as Lapland and the Baltic Island of Öland. But ever productive in his Uppsala professorial headquarters, Linnaeus inspired students, some of whom traveled widely, to collect and describe as many new species as they could find. Among them were Peter Forkål and Karl Peter Thunberg, the first field taxonomists to visit Asia, and the pioneering insect taxonomist Johan Christian Fabricius. The systematic exploration of the biosphere had begun, in what today can legitimately be called the Linnaean enterprise.

3 346 edward o. wilson Where the launching of global biodiversity exploration was an eighteenth-century achievement, the great advance of the nineteenth century, the third landmark in the series of four I would like to recognize, was the introduction of evolutionary theory as the leitmotif of biodiversity studies. The first to promote this idea was Jean Baptiste Pierre Antoine de Monet de Lamarck, often called Chevalier de Lamarck. His Philosophie zoologique, published in 1809, argued that the world s multitudinous life forms can be organized into a phylogeny, a history of ancestors and descendants. But Lamarck s reasoning convinced few scholars of the value of phylogenetic classification or even of the fact of evolution. In fact, it ultimately turned out that his proposed mechanism of evolution was wrong. This is the theory of inheritance of acquired characters, in which changes in one generation induced by interaction with the environment tend to be passed on to the next generation. It remained for Charles Darwin, in his masterwork, On the Origin of Species, fifty years later, to provide massive and compelling evidence for the ongoing process of evolution. He also put forward the correct explanation for it: natural selection, whereby spontaneous mutations create hereditary variants, which compete for survival and reproduction, resulting in the gradual replacement of some variants by others over many generations. Darwin s theory of evolution by natural selection, although at first opposed on both religious and philosophical grounds, spread in influence steadily thereafter. In time it not only succeeded but became fully transformative throughout biology. The rise of Darwinism reminds us that a great scientific theory is like a sunrise. It illuminates the steeples of the unknown and then their dark hollows. In the 1920s and 1930s, the theory of evolution by natural selection was first fully integrated with genetics, to begin what came to be called the Modern Synthesis, then more fully with paleontology, ecology, and developmental and behavioral biology, and lastly with cell and molecular biology. Its first links to the social sciences and humanities are now being forged. Applied to systematics, evolutionary theory cemented the concept of phylogeny and validated classification above the species level based on phylogenetic reconstructions. What, then, is the fourth and correct advance in systematics? It is nothing less than the attempted completion of the Linnaean enterprise by a full mapping of Earth s biodiversity, pole to pole, viruses to whales, at every level of biological organization from the genome to the ecosystem. It aims to yield as complete as possible a cause-and-effect explanation of the biosphere, and a correct and verifiable family tree for all the millions of species in short, a unified biology. This is a task that, in spite of centuries of effort already devoted to

4 the linnaean enterprise 347 it, has only begun. How many species are there on Earth? Surprisingly, after generations of exploration we do not know to the nearest order of magnitude. Somewhere between 1.5 and 1.8 million species of plants, animals, and microorganisms have been discovered and given a scientific name, but estimates of the true number vary widely according to method. They have ranged from an improbably low 3.6 million to a high of 100 million or more. Examples from several groups of organisms provide a quick picture of how little we know about life on planet Earth. Approximately 60,000 species of fungi are now diagnosed and classified, but the true total number of species probably exceeds 1.5 million. Consider also the nematode worms, the most abundant animals on the planet, making up four out of every five animals, and so abundant that if it has been said all solid matter were removed from the surface of Earth, you could still see the ghostly outline of it in nematodes. These tiny animals are probably essential for the maintenance of healthy environments. Nematodes are known from about 16,000 species, but the real number could easily be in the millions. The dark matter of biodiversity is the bacteria, on which the existence of the rest of the biosphere certainly depends. As of late 2002, 6,288 species were known and classified, but about 5,000 occur in a single gram of fertile soil, virtually all unknown to science, and it s been estimated that in one ton of soil are found 4 million species. Even the largest and best-studied organisms are far from fully known. The global number of known frog and other amphibian species, and that of mammal species, have each grown in the past twenty years by one-fourth, from around 4,000 to 5,000 described species. Each year about 2,000 new species of flowering plants are added, and the total number of flowering plants could easily rise from the present 275,000 to considerably more than 300,000. I am among the biologists who are now urging that it would be of enormous benefit to science and humanity to get on with the exploration of Earth s biodiversity and aim for its completion, not as a destination eventually to be reached but as a concrete goal with a timeline. The prospect of the initiative has been newly and greatly accelerated by new technology, in particular high-resolution digital photography, Internet publication, and rapid DNA sequencing. A census and encyclopedia of all or almost all species on Earth is needed and can be achieved, many of us believe, within twenty-five years. The quantum leap implicit in this ambition is made clear when it is realized that, whereas very roughly 10 percent of Earth s species, to pick a reasonable guess, have been discovered and classified during the past two hundred and fifty years, beginning with the binomial system of Linnaeus in the eighteenth century, it now seems possible to complete the

5 348 edward o. wilson remaining 90 percent of species in one-tenth that time. The total cost, spread over twenty-five years and many countries, would be comparable to that of the Human Genome Project, say $3 billion, with most of the investment in training and organization front-loaded to put the enterprise in full motion. Upon this effort can be built an Encyclopedia of Life, an electronic page for each species known, virus to whale, available everywhere by a single access on command. The page would contain the scientific and, if available, common name of the species, a pictorial or genomic presentation of the primary type specimen on which the name is based, and a summary of the species diagnostic traits. The page would open out directly, or by linkage to other databases, to a summary of everything known about the species biology and its perceived practical importance for the environment and humanity. This knowledge will serve human welfare in diverse ways, quickly and up front. The discovery of wild plant species adaptable for agriculture, of new genes for enhancement of crop productivity, and of new classes of pharmaceuticals will be speeded. The outbreak of pathogens and harmful plant and animal invasives will be better anticipated and more easily halted. Never again need we overlook so many golden opportunities in the living world around us, or be so surprised by the sudden appearance of destructive invasive species and pathogens springing from it. And not least, encyclopedic knowledge is what we need in order to save as much as possible of the rest of life for future generations. The Linnaean enterprise has never faltered in its logic and forward progress, nor dimmed in its purpose. Its present status can be counted as a successful product of the Enlightenment.