NOTES Chapter One IOf the works published during his lifetime, four constitute Darwin's main contribution to evolution theory. These are On the Origin of Species by Means of Natural Selection. or the Preservation of the Favoured Races in the Struggle for Life (1859), The Variation of Animals and Plants Under Domestication (1868), The Descent of Man. and Selection ill Relation to Sex (1871) and The Expression of Emotions in Man and Animals (1872). After initial work in the late 1830s and the early 1840s, Darwin returned to work on his theory of evolution in 1856, and had produced over a thousand pages of text when the letter from A. R. Wallace arrived presenting Wallace's very similar theory of evolution. After the joint presentation to the Linnean Society of London of excerpts from Darwin's 1842-44 work and Wallace's articles and letters of the 1850s, Darwin then produced an "abstract" of his own work, which became the Origin of Species. The much longer work that he was producing at the time has subsequently been published in several parts. Two chapters of Darwin's 1856-58 manuscript were published during Darwin's lifetime as The Variation of Animals and Plants under Domestication, while the rest was published by R. C. Stauffer under the title Charles Darwin's Natural Selection (1975). This work is of interest because it contains many footnotes by Darwin referencing the source of his ideas and facts. These, along with many digressions, were not included in the shorter Origin of Species, in keeping with its role as an "abstract." 2Darwin accepted that characters acquired during the life of an individual could be transmitted to its progeny. Unlike Lamarck, however, he rejected the notion that in the higher animals this was mediated by an act of willing. Rather, he sought a physiological mechanism of inheritance capable of producing such a result, and the theory of pangenesis was the result. According to this theory, as set out in The Variation of Plants and Animals under Domestication (1868), tiny particles, or "gemmules" are produced by each bodily organ and encapsulate its state of development. These gemmules congregated in the sexual organs, to be passed on through procreation and activated in progeny. Activation resulted in the parental character being reproduced in the children, providing the basis for a belief in the acquisition of acquired characteristics. Darwin was concerned about the speculative nature of his thesis, and referred to it in letters as a "working hypothesis." He maintained it because it allowed him to include a large number of facts of heredity under a general hypothesis. The subsequent demonstration by August Weismann 185 186 NOTES FOR PAGES 5 TO 7 and others that the theory of pangenesis was false provides an example of a part of Darwin's theory that has been refuted. 3Darwin provided lists of factors of variation in his Essays of 1842 and 1844, Natural Selection, Origin of Species, and Variations of Plants and Animals. In the chapter "Laws of Variation" in Natural Selection, his list was as follows: the immediate or direct action of external conditions, acclimatization, effects of use and disuse of structure, correlation of growth, and compensation or balancing. In the Origin of Species, a similar, but not quite identical list was given at the head of the chapter on laws of variation. Darwin also considered that wide-ranging, much diffused, and common species varied most, as did species in larger genera as compared to those in smaller ones. 4In An Essay on the Principle of Population (1803), Malthus argued that human population increased more rapidly than food supply, resulting in over­ population, and the consequent lowering of the living standard. Malthus took this as an argument against revolution, the French in particular, as there was no way to permanently improve the living conditions of the mass of the population. Whereas Malthus restricted his work to human populations and was concerned mainly with political implications, Darwin extended the concept to all species, and drew the biological conclusion that the ensuing struggle for existence was the condition upon which natural selection acted. 5In a hypothetical and simplified example, the characteristic might be the length of the claws of an animal that procured its food by digging it up from the ground. If the claw length were too small, the animal would not be successful in feeding itself, while those animals with longer claws would succeed and "prosper," as measured by the number of their progeny. 6In Natural Selection, Darwin was explicit in indicating that Milne-Edwards' concept of biological division of labor suggested his notion of divergence of character: "The doctrine is in fact that of the 'division of labour,' so admirably propounded by Milne Edwards, who argues that a stomach will digest better, if it does not, as in many of the lowest animals, serve at the same time as a respiratory organ; that a stomach will get more nutriment out of vegetable or animal matter, if adapted to digest either separately instead of both." (1856-58: 223) Nonetheless Darwin rejected Milne-Edwards' opposition to evolution, and he noted that the same concept, that of division of labor, could be used in both an evolutionary and non-evolutionary context. Biological division of labor, which Darwin also referred to as the "law of economy," reappeared in modified guise as divergence of character in Darwin's mature theory, adding an element that was absent from his 1842 and 1844 Essays, though present in Wallace's 1855 paper. At least one commentator (Brackman, 1980) argued that Darwin took the notion of divergence of character NOTES FOR PAGES 7 TO 14 187 from Wallace without acknowledgement, and that Wallace, rather than Darwin, was the "true" inventor of the modern theory of evolution. But if Darwin took the idea of divergence of character from Wallace, then he also took it from Milne-Edwards, and on this point the acknowledgment was explicit in Natural Selection. 7Darwin stated in his text accompanying the diagram of the tree of evolution: "But I must here remark that I do not suppose the process ever goes on so regularly as is represented in the diagram, though in itself made somewhat irregular, nor that it goes on continuously; it is far more probable that each form remains for long periods unaltered, and then again undergoes modification." (1859, 1: 168) The term "continuous" referred to the rate of change, rather than the process of change, and Darwin admitted that periods of stasis might be followed by periods of rapid change - as Eldredge and Gould (1972) would generalize in their theory of punctuated equilibrium. At no time did Darwin recognize non-continuity in the process of change, since this would amount to saltationist leaps which he held to be inimical to his theory. 8Darwin's main writings on plants were: On the Various Contrivances by which British and Foreign Orchids are Fertilised by Insects (1862), On The Movements and Habits of Climbing Plallfs (1865), Insectivorous Plants (1875), The Effects of Cross and Self-Fertilization ill the Vegetable Kingdom (1876), The Differellt Forms of Flowers on Plants of the Same Species (1877), and The Power of Movement in Plants (1880). 9The term "biopsychism" was used by Ernst Haeckel in "Our Monism: The Principles of a Consistent, Unitary World-View" (1892), where he distinguished between panpsychism, biopsychism, and zoopsychism as three theories of the scope of the mental - ranging from panpsychism as universality of mind to zoopsychism which restricted mind to animals alone. 10 Aristotle's theory analyzed terrestrial matter in terms of the four basic elements - earth, air, water, and fire - while a fifth element - aether - was reserved for celestial phenomena. Each of the four earthly elements was based on two non­ contradictory qualities - hot or cold, wet or dry. For example, water was wet and cold, and could be transformed into air by replacing the quality of cold with that of hot, producing the element which was both wet and hot - air. The quantity of "hot" or "cold" required was irrelevant, since all that counted was the fact of the qualitative replacement. llDarwin's quantitative view of the character of change was related, though not the same, as his defense of the thesis of gradualism. Gradualists hold that species form slowly over very long periods of time. This is an empirical consideration, and can be confirmed or refuted by measuring rates of speciation. 188 NOTES FOR PAGES 14 TO 16 Rapid speciation followed by long periods of stasis can occur within a continuous evolutionary process, as in the punctuated equilibrium of Eldrege and Gould (1972). The condition is that rapid speciation occur over a finite, albeit small period of time, and not occur in an "instant" or just one generation, as hypothesized by the saltationism of Goldschmidt's (1940) "hopeful monster." It is possible to have a continuous but non-gradualist theory of evolutionary change, and the Gould-Eldredge punctuated equilibrium theory need not be considered as saltationist. 12The problem of the status of "species" has been the subject of considerable debate, an example of which is Michael T. Ghiselin, "Species Concepts, Individuality, and Objectivity" (1987), as well as the reply by Ernst Mayr, "The Ontological Status of Species: Scientific Progress and Philosophical Terminology" (1987), both in Biology and Philosophy. The problem of the status of species has also been the subject of a long lasting debate in the pages of Journal of Systematic Biology. 13A simplified example of Darwin's quantity-quality distinction can be illustrated as follows: consider two populations of animals co-descended from a single parental stock, which differ in that members of population X are on the average 2" taller than members of population Y.