For two years in the late 1970s I followed in the footsteps of Carl Linnaeus: I toiled in the field of taxonomy. The small corner of nature's jigsaw puzzle that I tackled was a group of marine sponges whose baffling variability defied easy classification. I considered their color and form, examined their skeletal architecture, counted their spicules, noted the shape of their larvae, and pondered which of these characters could be used to separate my subjects into meaningful categories.
My youthful foray, long since abandoned, resulted in a classification scheme for 43 species of New Zealand sponge. It also gave me an appreciation for the towering achievement of Carl Linnaeus, the father of modern taxonomy. Linnaeus, born 300 years ago this month, classified and named more than 4,000 animals and nearly 8,000 plants. As superhuman a feat as that was, the illustrious Swede also devised the very system of classification that I and every other student of taxonomy have used since then.
The eldest son of a small-town curate, Linnaeus chose to pursue his father's recreational interest in plants and became the greatest botanist of his time. He was also a successful physician, a charismatic lecturer, a devoted mentor, an enthusiastic gardener and a prolific writer. He not only sorted and systematized all the known species of his day but also pioneered the study of how indigenous people use plants for medical and other purposes, earning another sobriquet: the father of ethnobotany. The simplicity and logic of his taxonomic system made natural history accessible to amateurs, ushering in the Victorian passion for nature. Jean Jacques Rousseau said of him, "I know no greater man on earth."
Prior to Linnaeus, taxonomy had been a shambles. There were complex names for even the commonest species, and multiple criteria for classifying them. The tomato, for example, was Solanum caule inermi herbaceo, foliis pinnatis incises—the solanum with the smooth stem which is herbaceous and has incised pinnate leaves. Linnaeus' genius was to apply the social hierarchy of his day, with its kingdoms, provinces, parishes and villages, to the natural world. He slotted plants and animals into a framework of five main categories—kingdom, class, order, genus, species. Almost incidental to his encyclopedic audit of the natural world was his decision to call each living thing by just two Latin names, representing genus and species. This innovation, known as binomial nomenclature, has proved to be Linnaeus' greatest gift to posterity. Any time Homo sapiens mention Felix domestica (the house cat) or Lycopersicon esculentum (the tomato) or Callyspongia ramosa (one of my beloved sponges) Linnaeus' naming system is invoked. Out of the babel of competing nomenclatures he forged a single, universally applicable scientific language.
At times, Linnaeus thought of himself as the second Adam. "Deus creavit, Linnaeus disposuit," he liked to say—God created, Linnaeus organized. The frontispiece of his Systema naturae, his magnum opus, depicts its author in the Garden of Eden, evidently applying Linnaean names to freshly minted creatures. First published in 1735 as an 11-page tract, Systema naturae was Linnaeus' tabulation of the three recognized realms of nature: animals, plants and minerals. He kept adding to it throughout his life, and when the 13th edition was published in 1770, eight years before his death, it had grown to 3,000 pages. It was the last species omnibus ever attempted by a single person. Such was the proliferation of scientific discovery after Linnaeus (in part because his classification system was so comprehensive and easy to use) that no one individual could ever again hope to take nature's measure.
But how much longer will the Linnaean system last? Recently it has come under attack from some taxonomists who believe its structure is too inflexible to cope with the explosion of knowledge unleashed by DNA analysis. Today's young Turks of taxonomy want to abolish the strict ranked hierarchy of family, order, class, etc. In its place they advocate "clades," groupings that are based on genetic relationships and can be expanded, contracted or redefined as new kinships are discovered. For now, the traditionalists outnumber the iconoclasts, and Linnaean-style classification remains the gold standard.
Linnaeus struggled to find universally applicable characters by which to categorize the myriad manifestations of life. In classifying plants, Linnaeus chose to focus on sexual characteristics. He placed plants into classes according to the number, length and distinctive features of their pollen-bearing stamens, and into orders according to their pistils.
The approach earned Linnaeus the ire of his more prudish colleagues. They objected to his lyrical descriptions of the love lives of plants. Bad enough that a flower's petals should be compared to the "bridal bed...perfumed with so many sweet scents in order that the bridegroom and bride may therein celebrate their nuptials with the greater solemnity," but when Linnaeus defined polyandrous flowers as having "twenty males or more in the same bed as the female," this was too much. "Who would have thought that bluebells and lilies and onions could be up to such immorality?" jibed one critic, who dismissed the entire system as "loathsome harlotry" unworthy of the Creator.
For animals, Linnaeus' criteria were less provocative. He grouped mammals according to teeth, toes and teats; fish by fin bones; insects by wings; and birds by feet and beaks. He recognized that his categories for plants and animals were arbitrary and his classification no more than a crude stab at divining nature's pattern, but they would have to do. Despite their shortcomings, Linnaeus' names for the roughly 12,000 organisms he examined over the course of his life became the starting point for biological classification.
Linnaeus' theories and methods were always rooted in the real world. At a time when taxonomists were largely an indoor species, inhabiting lecture halls and libraries and scrutinizing pressed flowers, pinned insects and pickled vertebrates, Linnaeus was a dirt-under-the-fingernails scientist. For more than 20 years he conducted public excursions in the countryside around Uppsala—possibly the world's first guided nature walks. He did so partly to supplement the income from his impecunious postings as curator of the Uppsala botanical garden and then as professor of medicine at Uppsala University. Participants (as many as 300 per excursion) paid him in whatever currency they could afford: coins, hats, socks, books, buttons.