It has often been noted that the synthetic theory of evolution in the 1930s and 1940s was mainly the work of zoologists such as Ernst Mayr (1904–2005) and that this created a lasting, zoocentric bias in contemporary understanding of evolution. Contributions of microbiologists and botanists in particular were actively excluded or depreciated, perhaps for the simple reason that evolution in higher vertebrates involves patterns and processes that are also familiar from humans. Charles Darwin himself, in contrast, had an intense interest in plants and lower animals, especially colonial metazoans, and dedicated much of his natural historical and experimental work to them. His son Francis spoke of his father's ‘passionate desire to understand the machinery of all living things’, and this especially included forms of life that did not permit a clear-cut distinction between individuals, the organic parts they consist of, and the populations they form. As a consequence, Darwin often ignored the distinction between physiology and developmental biology on the one hand, and evolutionary biology on the other, that has become so entrenched in the wake of Mayr's philosophy of biology. Physiological and evolutionary research went hand in hand for him, especially later in life.
Peter Ayers's The aliveness of plants introduces the reader to the intellectual and cultural background that informed this kind of thinking. It follows the botanical pursuits of four generations of Darwins: from Erasmus Darwin's (1731–1802) translations and poetic renderings of Carl Linnaeus's key botanical works in the 1780s, to the private interest of his son Robert Waring (1766–1848) in the horticulture of tropical plants; from the country house experiments of Charles Robert Darwin (1809–1882) on plant movement and fertilization to the research of his son Francis (1848–1925) into stomatal physiology at Cambridge University's Botanical School. But Ayers is not myopically concerned with the scientific achievements of the Darwins only. By exploring the literary contexts that informed these achievements—experiments and publications of all major European plant physiologists, including Stephen Hales (1671–1761), Jan Ingen-Housz (1730–99), Joseph Priestley (1733–1804), Jean Senebier (1742–1809), Antoine Lavoisier (1747–94), Nicolas-Théodore de Saussure (1767–1845), Henri Dutrochet (1776–1847), Jean-Baptiste Boussingault (1802–87), John Burdon Sanderson (1828–1905), Julius Sachs (1832–97), Michael Foster (1836–1907), Wilhelm Pfeffer (1845–1920) and Frederick Frost Blackman (1866–1947)—he has effectively accomplished a history of plant physiology in the long nineteenth century, a period during which both the social status of scientists and the institutional landscapes of science underwent crucial and far-reaching changes. Erasmus, Charles and Francis represent these transitions prototypically, the first being an amateur, the second a gentleman-naturalist, and the third a professional scientist (p. 15).
The author, an emeritus professor at the University of Lancaster, is himself an eminent plant physiologist and pathologist and has previously contributed to the history of his discipline with a biography of the mycologist Harry Marshall Ward (1854–1906). Accordingly, his interests lie primarily in what in an old-fashioned way may be called the ‘internal’ history of plant physiology: the evolution of its problems, the various ways in which these problems were addressed experimentally, and, ultimately, ‘the progress we have made in our scientific understanding’ (p. 1) along the way. A first, very short chapter defines photosynthesis, plant growth and their impact on the chemical composition of our planet's ecosystem and atmosphere as the ‘green threads’ of the story that is to follow. Within this very general frame a wide range of subjects in plant physiology are treated in great historical detail. Chapter 4 deals with the late-eighteenth-century debate about the function of leaves in photosynthesis, respiration and transpiration, the state of which Erasmus summarized in Phytologia (1789). Chapters 6 and 7 turn to what Francis called his father's ‘physiological period’ from 1860 onwards, and shifts the thematic focus to the problem of plant movement and the famous debate evolving between the two Darwins and Sachs about whether or not the root tip, as Charles had formulated, ‘acts like the brain of lower animals’. Chapter 8 recounts Francis's experimental work on the function of stomata and geotropism, which went along with the development of intricate measuring instruments. Chapters 3 and 5 are more concerned with plant natural history—plant biogeography and flower morphology as they were reflected in Charles's Origin and related works—but do a good job in painting the background against which plant physiology wished to stand out as proper science.
Ayres's ‘internalist’ stance does not mean that social and institutional factors are ignored. The second chapter explains how the ‘fortunes of the Darwins’ were tied to land ownership—Robert Waring Darwin in particular exhibiting an ‘aggressive risk-taking attitude to investment’ (p. 8)—and the last two chapters return to the motive of ‘fortune’, by elaborating on intergenerational relations and legacies within the Darwin family. The remaining chapters, too, take care to indicate the often intriguing, social and institutional, settings that shaped and enabled plant physiological research. Erasmus's dedication of Phytologia to Sir John Sinclair (1754–1835), then President of the Board of Agriculture (p. 35); the simple observation that Charles's book Effects of Cross and Self-Fertilization in the Vegetable Kingdom (1876) focused on food crops and their evolution (p. 77); Francis's collaboration with his brother Horace's Cambridge Instrument Company (p. 124)—details like this provide ample food for thought for future social and cultural historians of science should they venture to fill in what remains one of the most glaring research lacunae in their field: the rise of plant science in nineteenth-century contexts that were defined by medical and agro-industrial concerns.
What, then, about evolutionary theory? Ayres reveals a layer of thought in Charles Darwin that underpinned his physiological researches and was probably far dearer to him than the rather superficial question of the sole efficacy of natural selection in evolution. Fundamentally, Ayres maintains, Darwin was ‘dealing with living things as if they had “goal-oriented” actions’. Circumnutation in plants—or as Darwin put it, ‘the continuous bowing movement directed successively to all points of the compass … to favour the shoot finding a support’—exemplified the kind of explorative and expansive agency that the competitive struggle for life presupposes. It is on this metaphysical point that Sachs, a staunch mechanicist, disagreed with Darwin, as would most self-professed neo-Darwinians today.
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