Nature has long been perceived as three kingdoms, like the three realms that obeyed Queen Anne, but we know that empires in the eighteenth century (as always) had fuzzy and troublesome boundaries. That century was also the epoch of taxonomy, finding a place for everything in the great scheme of things, from Linnaeus's arrangement of plants to Lavoisier's table of simple substances. Voyages of discovery, establishment of great trading companies and settlement of European colonies meant that more and more collections of animals, vegetables and minerals reached metropolitan centres, and describing, naming and classifying them became essential. Like the chaotic waters in Genesis over which the Spirit moved, they needed order to be imposed upon them, and underlying their profusion naturalists expected to find the clarity and simplicity that Newton had revealed for the solar system. The desideratum was a natural system reflecting God's plan, where natural frontiers separated the various kingdoms and provinces, and organisms fell into natural groups or families (a word used without evolutionary significance) determined from a wide range of characteristics. Some naturalists, notably Buffon, believed that this was impossible, indeed wrong-headed, because organisms belonged on a great chain or ladder of creation rather than in distinct groups; others thought that it was impractical, and that artificial systems based upon a single character should be imposed. Susannah Gibson, in this attractive and readable book, looks at the awkward squad of misfits that cut across categories and set naturalists wondering and sometimes squabbling as they sought clinching evidence, not only with improved microscopes but also from chemistry, to enable them to place ambiguous organisms.

She begins with a rapid run-through from Aristotle to Joseph Banks before beginning the serious business with ‘Animal’, where on the frontier were the ‘zoophytes’, whose status was in serious doubt (as their name implies). Here Abraham Trembley and John Ellis are her explorers. Trembley's experiments on the polyp, which looked to the casual eye like a plant, revealed not only the way its parts would regenerate if cut off, but also its activity: trapping food, and moving in somersaults. It was apparently a very odd animal. So were ‘corallines’ (minute creatures found off the British coast) which Ellis investigated, getting the great botanical artist Georg Ehret to draw them, and doing chemical tests to establish their animal nature – animal tissue heated up gives an ammoniacal smell, diagnostic to the trained nose. ‘Mineral’ involves the author in ‘fossils’, as gradually some came to be accepted, despite their strangeness of shape and dimensions, as remains of animals and plants, turned somehow to stone. We meet the famous hoax played upon the too-trusting Johann Beringer, whose collectors created the specimens they then found, and conclude with William Smith and his use of fossils to elucidate strata. ‘The fourth kingdom’ begins with the sundew, preying upon insects, and ‘perceptive’ or sensitive plants apparently also displaying characteristics of animals; then takes us through the enthusiastic reception of the Linnaean system and the ‘loves of the plants’ through James Smith and Erasmus Darwin, concluding with the long-running and sometimes heated arguments about vitalism or mechanism that continued into the nineteenth century, with participants including Stephen Hales, Thomas Percival and Thomas Andrew Knight. This work threw doubt upon the sufficiency or applicability of the historic tripartite system, and the epilogue reminds us how cell theory, evolution, germ theory and the study of microorganisms, and developments in physiology, have made ‘animal, vegetable or mineral’ obsolete in science.

Though much of Susannah Gibson's story, and most of her characters, will be familiar to readers of BJHS, as a short and readable introduction to the eighteenth-century preoccupation with taxonomy her book is very useful, and it has full scholarly notes and recommendations for further reading. She effectively places in their various contexts her men of science – and except for Rosalind Franklin in the epilogue, that's what they are – and her focus upon boundaries and anomalies gives a unity to what could be a sprawling story. The book casts light on scientific societies, communication, rivalries and priority disputes as well as the love and curiosity that drove people into the study of nature when they might have found a more lucrative pursuit. I hope it will be widely read and enjoyed among the general readers to whom it is particularly addressed.