The C. Warren Irvin, Jr., Collection of Darwin and DarwinianaIsland 3
The controversial aspects of Darwin's work are those which relate to
the origin of man and to his relationship to the primates and other mammals.
To avoid controversy, Darwin deliberately skirted this topic in On the
origin of species. Nontheless, contemporary debate centred on the ape/angel
controversy, notably at the 1860 Oxford meeting of the British Association
at which Darwin's leading supporter, T.H. Huxley, dealt devastatingly with
the flippant criticism of Bishop Wilberforce of Oxford.
In the summer and autumn of 1861 Darwin studied the orchid, concentrating on the relationship between form and reproductive function in different species of the plant. Minor variation in the morphology of different species can be correlated precisely to the behavioural patterns of specific insects vital to the cross-pollination of a given species. The relevance of such variations to the theory of natural selection is obvious. Darwin's interest in the response and adaptation of plants to external stimuli is an interesting echo of the views of his grandfather Erasmus, who held (as Darwin himself would never hold) that plants consciously adapt to their environments.
Darwin worked slowly on The variation of animals and plants in the years following the 1859 publication of On the origin of species. Care was essential as Darwin intended to formulate genetic theories explaining developmental processes described in the Origin. The two-volume work contains a wealth of detail. In the numerous varieties of the domestic dog, for example, Darwin observed both the great genetic adaptibility of the species and the probability that similar diversity existed among prehistoric wolves and jackals. In contrast, far less variation exists in the less tractable, more recently domesticated cat. The obvious and often simple mutability of genetically transmissible characteristics in domestic animals and plants has obvious implications for the feasibility of genetic selection in a less controlled environment.
The expression of the emotions in man and animals is a pendant to the 1871 Descent of man. In contrast to those scientists, notably Sir Charles Bell, who held that the musculature of the human face is uniquely designed for the expression of the emotions, Darwin outlined the affinity of the human facial structure to that of other primates, detailing behavioural similarities in the emotional expression of man, primates, and other mammals. By demonstrating a cross-cultural pattern of human expression and the sharing of similar modes of emotional expression by a number of species, the book indicates that "man's emotional expressions are as much a product of his evolution as are his anatomy and physiology" (Bowlby, p. 202).
Darwin's published botanical studies indicate a marked interest in aspects of plant physiology which relate "behavioural" patterns of the vegetable and animal kingdoms - for example, his studies of adaption and variation in the fertilization of orchid species and of the power of movement in plants. Insectivorous plants, also an interest of Erasmus Darwin's, seem, therefore, an inevitable preoccupation. In the summer of 1860, in the early stages of this study, his wife Emma wrote to Lady Lyell: "At present he is treating Drosera just like a living creature and I suppose he hopes to end by proving it to be an animal". Drosera rotundifolia, the Sundew, traps insects which stick to its leaves, curling the leaves around them and slowly absorbing and digesting their bodies.
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The central thesis of The effects of cross and self-fertilization is that the morphology of plants encourages and facilitates cross-pollination in preference to self-fertilization. Darwin showed that even those plants capable of self-fertilization almost invariably produce stronger, more vigorous offspring when cross-fertilized. The demonstration that the form of plants adapts to encourage effective cross-fertilization and that cross-fertilization produces stronger offspring further supports the principle of natural selection. Darwin regarded The effects of cross and self-fertilization as a complement to his 1862 work on orchids.
In 1864 Darwin published On the movements and habits of climbing plants in the Journal of the Linnaean Society. Further studies are described in the Power of movement in plants. Darwin identified light as the stimulus which triggers the twisting mechanism of climbing plants. Close observation indicates that the coiling and twisting ability exists in all plants: shoots groping to the surface spiral in constant circles; roots move in a similar pattern. Given the absence of an identifiable nervous system in plants (Darwin did not share his grandfather's view of plant physiology), he was unable to solve the crucial problem of the transmission of stimuli from the tips of shoots and roots to other growth areas. His present-day successors, who have identified hormones as the transmitter of stimuli, still to work to understand this problem.
In the 1830's Darwin noted that lime spread at his father-in-law's estate lay under two and a half inches of soil after ten years. Other observations (chalk scattered at his own home sank seven inches in 29 years) indicated either that material deposited on open ground sinks at the rate of 0.25 inches a year, or that a layer of vegetable mould of that thickness is deposited annually through some unidentified agency. Darwin identified earthworms, passing through and turning the soil, eating and excreting vegetable matter, as the agent responsible for the deposit. He and his son Francis calculated that at his home, Down House, earthworms annually carry some 18 tons of earth per acre to the surface. The formation of vegetable mould, Darwin's last book, is unrelated to the topics of natural selection and genetic adaptation which form a common thread through much of his research. It was, however, a greater commercial success than On the origin of species, probably because of the reading public's familiarity with earthworms.
On the origin of species was reviewed for the American journal
of science by Asa Gray, Fisher Professor of Natural History at Harvard,
with whom Darwin had corresponded on the subject of evolutionary theory.
Though Gray was more concerned than Darwin to reconcile science and religion
(typically an American rather than a British preoccupation) he became Darwin's
staunchest American defender. Significantly it was in the United States
that the nebulous doctrine of Social Darwinism, the practical application
of the survival of the fittest to the shaping of society, was used to justify
westward expansion and the militant capitalism of the Gilded Age. Darwin's
books found a ready readership in North America, both in the authorized
editions published by Appleton and in numerous but legal piracies. The
first American edition of Darwin's final book, The formation of vegetable
mould, is shown here.