Humboldt,Darwin, and population

Conclusions I have attempted to clarify some of the pathways in the development of Darwin's thinking. The foregoing examples of influence by no means include all that can be found by comparing Darwin's writings with Humboldt's. However, the above examples seem adequate to show the nature and extent of this influence. It now seems clear that Humboldt not only, as had been previously known, inspired Darwin to make a voyage of exploration, but also provided him with his basic orientation concerning how and what to observe and how to write about it. An important part of what Darwin assimilated from Humboldt was an appreciation of population analysis as a tool for assessing the state of societies and of the benefits and hardships which these societies can expect to receive from the living world around them.Darwin exhibited in his Journal of Researches a casual interest in the economic and political conditions of the countries he visited, but these considerations were much less important to him than to Humboldt. Instead, Darwin, with the assistance of Lyell's Principles of Geology, shifted from Humboldt's largely economic framework to a biological one built around the species question. This shift led Darwin away from a consideration of how the population biology of animals was related to man's economy to focus instead upon how population biology fitted into the economy of nature.Humboldt's Personal Narrative served very well as a model for Darwin's Journal of Researches, thereby helping Darwin gain scientific eminence. The Journal of Researches, like virtually all of Humboldt's writings, was a contribution to scientific orthodoxy. But Darwin had, along the way, acquired an urge to do more than just add his building blocks to the orthodox scientific edifice. He decided to rearrange those blocks of knowledge into a different structure, and for that task neither Humboldt's Personal Narrative nor any other of his works could serve as a model. Humboldt had lacked the confidence which Darwin needed that biogeography and the origin of species could be understood. Humboldt had not explored very far the possible connections between biology and geology. Nor had he provided a general synthetic account of population biology. Had he done so, he might have been more explicit about the extent of his endorsement of Malthus. But even if he had, Humboldt's strong orientation toward cooperation would probably have inhibited his recognition of the importance of competition in nature.Lyell, who had also benefited from reading Humboldt, gave Darwin insights that were lacking in Humboldt's Personal Narrative. Lyell admirably demonstrated how stratigraphy, paleontology, biogeography, and population biology could be interrelated, and his reasons for doing so were essentially the same as Darwin's. Lyell's understanding of biogeography and ecology came from the writings of Augustin-Pyramus de Candolle as much as from Humboldt's, and from the former Lyell derived an appreciation for the importance of competition and also a confidence that the mysteries of biogeography could be explained.¹¹⁷ Furthermore, Lyell's discussion of all these subjects and also of evolution in his Principles of Geology is a good synthetic argument that was the ideal model for Darwin's greatest book.Darwin, having become convinced that species change through time, was able to synthesize in his mind the contributions which he had derived from the writings of Humboldt and Lyell as they applied to the species question. When Darwin wrote his Journal of Researches there were two large gaps in his thinking about evolution that bothered him—the mechanism of evolution and the causes of extinction. It was only after reading Malthus in 1838 that he realized, as Lyell had more or less pointed out, how important was competition in nature. He now had the general outlines for his theory, and in the 1845 abridged edition of his Journal, now retitled The Voyage of the Beagle, he inserted a fuller discussion of competition in nature which showed his awareness of its importance as an ecological factor.¹¹⁸ An abridged version of this paper was presented at the meeting of the History of Science Society in Washington, D.C., on 29 December 1969.     

Charles Darwin’s <Emphasis Type="BoldItalic">Beagle</Emphasis> Voyage,Fossil Vertebrate Succession,and “The Gradual Birth &; Death of Species”

The prevailing view among historians of science holds that Charles Darwin became a convinced transmutationist only in the early spring of 1837, after his Beagle collections had been examined by expert British naturalists. With respect to the fossil vertebrate evidence, some historians believe that Darwin was incapable of seeing or understanding the transmutationist implications of his specimens without the help of Richard Owen. There is ample evidence, however, that he clearly recognized the similarities between several of the fossil vertebrates he collected and some of the extant fauna of South America before he returned to Britain. These comparisons, recorded in his correspondence, his diary and his notebooks during the voyage, were instances of a phenomenon that he later called the “law of the succession of types.” Moreover, on the Beagle, he was following a geological research agenda outlined in the second volume of Charles Lyell’s Principles of Geology, which implies that paleontological data alone could provide an insight into the laws which govern the appearance of new species. Since Darwin claims in On the Origin of Species that fossil vertebrate succession was one of the key lines of evidence that led him to question the fixity of species, it seems certain that he was seriously contemplating transmutation during the Beagle voyage. If so, historians of science need to reconsider both the role of Britain’s expert naturalists and the importance of the fossil vertebrate evidence in the development of Darwin’s ideas on transmutation.     

Hooker and islands1

Sir Joseph Dalton Hooker (1817–1911), friend and scientific confidant of Charles Darwin, lectured in 1866 on ‘Insular floras’ at the Annual Meeting of the British Association for the Advancement of Science. His interest and knowledge of islands had been aroused when he travelled to the Antarctic aboard the Erebus under Sir James Clark Ross from 1839–43. On his return, Darwin passed on to Hooker the botanical collections he had made on the Beagle voyage, including those from the Galapagos. Hooker's conclusions from these and from his own material and experiences were important to Darwin as he developed the ideas that culminated in the publication of the Origin of Species. The 1866 lecture provided a focus for subsequent and informative studies on evolution, and islands continue to provide invaluable natural laboratories for evolutionary biology and genetics. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96 , 462–481.     

Why Darwin rejected intelligent design

As a Cambridge University undergraduate Charles Darwin was fascinated and convinced by the argument for intelligent design, as set forth in William Paley’s 1802 classic, Natural Theology. Subsequently, during his five-year voyage on HMS Beagle (1831–1836), Darwin interpreted his biological findings through a creationist lens, including the thought-provoking evidence he encountered during his historic visit to the Galápagos Islands in September and October 1835. After his return to England in 1836 and his subsequent conversion to the idea of organic evolution in March 1837, Darwin searched for a theory that would explain both the fact of evolution and the widespread appearance of intelligent design. His insight into the process of natural selection, which occurred in September 1838, provided this alternative explanation. Darwin’s Origin of Species (1859) exemplifies his skillful deployment of the hypothetico-deductive method in testing and refuting the arguments for intelligent design that he had once so ardently admired.     

A new look at variation in Darwin's species of acorn barnacles

Darwin's studies on barnacles, begun to satisfy his curiosity about specimens from the Beagle , but later extended to the large collections of other naturalists, lasted for 8 years and produced a set of definitive monographs. Darwin was particularly troubled over the taxonomy of two groups of acorn barnacles, Balanus tintinnabulum and B. amphitrite , which he ultimately classified as clusters of wellmarked varieties. Recent studies, based on established taxonomic methods or on statistical treatment of morphometric data, suggest these are clusters of full species and that the 'intermediate' forms are just phenotypic variants. Darwin was also troubled by the small chthamalid intertidal barnacles, which he eventually grouped as varieties of a world-wide species, Chthamalus stellatur. Gel electrophoresis and morphometrics now show this to be a heterogenous assemblage of distinct species, some very different, others closer together, all with restricted geographical range, but all showing extreme variability in the characters normally used for classification.
Darwin's difficulties with the classification of the highly varying barnacles, and his anatomical studies on these peculiar animals, must have had considerable influence on the development of his theories about natural selection, more than is usually acknowledged by writers on evolution. These 'lost years' were in fact a period of intense zoological enquiry, and Darwin's change in attitude with regard to species and variation in nature underwent a big change, as can be seen from the letters and from the differences between the early drafts written before the barnacle work and the later Natural Selection and The Origin. Whether we regard the difficult groups of Balanus as clusters of species or clusters of varieties, they still draw attention to evolutionary processes as in Darwin's day.     

Darwin's "beloved barnacles": tough lessons in variation

In 1846, burdened by insecurity and self-doubt, and having been convinced that he needed to study some group of organisms closely, Darwin embarked on an eight-year odyssey in the protean and perplexing world of barnacles. At the time, he was searching for evidence in support of his theory of evolution by natural selection. In the course of his long study of barnacles, however, he was not just validating his preexisting theoretical system, but was also modifying his views on such fundamental aspects as the universality of individual variation, which is the focus of this paper. According to this notion, the members of any population of living things are expected to exhibit sufficient differences from one another for natural selection to operate. By emphasizing the theoretical value of the barnacle project, my analysis contributes to the historiographic tradition which highlights the significance of the period between the first comprehensive formulation of the theory of evolution by natural selection in 1844 and its urgent publication in the late 1850s. In the course of these years, Darwin's theory was not just accumulating empirical laurels, but was also expected to adapt to a changing conceptual landscape.     

The meaning of Darwin's 'abominable mystery'

Charles Darwin's "abominable mystery" has come to symbolize just about all aspects of the origin and early evolution of flowering plants. Yet, there has never been an analysis of precisely what Darwin thought was so abominably mysterious. Here I explicate Darwin's thoughts and frustrations with the fossil record of flowering plants as revealed in correspondence with Joseph Hooker, Gaston de Saporta, and Oswald Heer between 1875 and 1881. I also examine the essay by John Ball that prompted Darwin to write his "abominable mystery" letter to Hooker in July of 1879. Contrary to what is generally believed, Darwin's abominable mystery has little if anything to do with the fossil prehistory of angiosperms, identification of the closest relatives of flowering plants, questions of the homologies (and character transformations) of defining features of flowering plants, or the phylogeny of flowering plants themselves. Darwin's abominable mystery and his abiding interest in the radiation of angiosperms were never driven primarily by a need to understand the literal text of the evolutionary history of flowering plants. Rather, Darwin was deeply bothered by what he perceived to be an abrupt origin and highly accelerated rate of diversification of flowering plants in the mid-Cretaceous. This led Darwin to create speculative arguments for a long, gradual, and undiscovered pre-Cretaceous history of flowering plants on a lost island or continent. Darwin also took refuge in the possibility that a rapid diversification of flowering plants in the mid-Cretaceous might, if real, have a biological explanation involving coevolutionary interactions between pollinating insects and angiosperms. Nevertheless, although generations of plant biologists have seized upon Darwin's abominable mystery as a metaphor for their struggle to understand angiosperm history, the evidence strongly suggests that the abominable mystery is not about angiosperms per se. On the contrary, Darwin's abominable mystery is about his abhorrence that evolution could be both rapid and potentially even saltational. Throughout the last years of his life, it just so happens that flowering plants, among all groups of organisms, presented Darwin with the most extreme exception to his strongly held notion natura non facit saltum, nature does not make a leap.     

Darwin's use of the analogy between artificial and natural selection

Conclusion The central role played by Darwin's analogy between selection under domestication and that under nature has been adequately appreciated, but I have indicated how important the domesticated organisms also were to other elements of Darwin's theory of evolution-his recognition of the constant principle of change, for instance, of the imperfection of adaptation, and of the extent of variation in nature. The further development of his theory and its presentation to the public likewise hinged on frequent reference to domesticates.We have seen that Darwin's reliance on the analogy between domesticated varieties and wild species was a bold and original step, in light of contemporary views on the nature of domesticates. However, as Darwin undoubtedly foresaw, his reliance on the analogy created difficulties as well as solving problems, and these began with his Malthusian codiscoverer of the principle of natural selection, Alfred Russel Wallace. Wallace's paper On the Tendency of Varieties to Depart Indefinitely from the Original Type, presented to the Linnean Scoiety along with the first public unveiling of Darwin's theory, states: We see, then, that no inferences as to varieties in a state of nature can be deduced from the observation of those occurring among domestic animals. The two are so much opposed to each other in every circumstance of their existence, that what applies to the one is almost sure not to apply to the other. Domestic animals are abnormal, irregular, artificial; they are subject to varieties which never occur and never can occur in a state of nature.⁶² Much has been made of the similarity of views of Darwin and Wallace, but this quotation surely reveals how utterly different their views were on what to Darwin was an important matter. Several critics of the Origin saw Darwin's reliance on the domesticates as his Achilles heel. As Young has pointed out, Samuel Wilberforce included the following passage in his attack on the Origin: Nor must we pass over unnoticed the transference of the argument from the domesticated to the untamed animals. Assuming that man as the selector can do much in a limited time, Mr. Darwin argues that Nature, a more powerful, a more continuous power, working over vastly extended ranges of time, can do more. But why should Nature, so uniform and persistent in all her operations, tend in this instance to change? Why should she become a selector of varieties?⁶³ Another critic, Fleeming Jenkin, found the analogy a weakness in Darwin's theory because of the limited extent of variation in any one direction in domestic animals and plants.⁶⁴ We have already seen that Darwin had confided a similar view to his notebook thirty years earlier, but changed his mind as a result of his profound study of domesticates. De Beer's reference to an English country gentleman's knowledge of domestic plants and animals and their breeding⁶⁵ fails totally to recognize the originality and depth of Darwin's knowledge of domesticates.Why did Darwin, against the currents of his time, rely so heavily on mankind's experience with domesticated organisms to shape his theory about species in nature? On reason is that only with domesticates was an approach that came close to experimental verification possible. Darwin fully realized the inadequacies of the experiment, as is emphasized by his repeated contrasting of selection under nature and selection by man. Yet the extensive experience and data of plant and animal breeders offered the only reliable base against which Darwin could continually challenge his views. As he wrote in the introduction to Variation, with domestication, man ... may be said to have been trying an experiment on a gigantic scale.⁶⁶ Given Darwin's high opinion of the quantitative work of Malthus and Quetelet (as emphasized by Schweber),⁶⁷ and his unremitting efforts to secure data by which to test his theories, it was inevitable that he should attach high significance to domesticated varieties. John Tyndall, in his Belfast address of 1874, said: The strength of the doctrine of Evolution consists, not in experimental demonstration (for the subject is hardly accessible to this mode of proof), but in its general harmony with scientific thought.⁶⁸ Darwin would have agreed with the latter thought, but I think he would have challenged the preceding one on the grounds that long experience with domesticated varieties did provide an element of experimental demonstration. It gave him confidence in his theory, and he used his vast knowledge of artificial selection boldly and creatively.     

Extending Darwin's investigations on the barnacle life-history

Darwin's magnificent study of the stalked, sessile and fossil barnacles, perhaps his greatest work, was started not many years after the systematic position of cirripedes within the class Crustacea had been accepted. It was completed at a time when histology and microtomy were not developed and when living specimens could only be seen on occasional visits to the seaside. Yet 130 years later it remains the standard text. It was on a visit to Tenby that he observed that barnacles were sensitive to vibration and, in seeking an acoustic organ, he mistakenly seized upon the oviducal gland. This led to an ever increasing series of misinterpretations of the female generative mechanism. Associated with this error was the belief that the ovary and cement glands were homologous in both cyprid and adult. He later confessed to “having blundered terribly over the cement glands”, but it was probably his search for examples of organs changing their function during evolution that led to this blunder. Similarly, he convinced himself mistakenly that the ovigerous fræna, which hold fast the egg masses to the mantle lining in stalked barnacles, became modified to gills in sessile barnacles. Darwin's interest in barnacle reproduction led to his discovery of complemental males attached to hermaphrodite individuals. He proved that they were dwarf cirripedes and not parasites. His knowledge that male and hermaphrodite flowers could co-exist helped him to accept that these apparently unnecessary beings could be present also in barnacles. We now know that complemental males are not confined to stalked barnacles but are also present in certain balanids. Though Darwin did not include the dioecious parasitic group, the Rhizocephala, in his studies, he recognized the wide repertoire of sexual arrangements from hermaphroditism to dioecy which now provides challenging material to our further understanding of sex allocation, control and evolution. Since Darwin dealt mainly with dried or preserved specimens he did not describe any of the details of the liberation of nauplii or the searching behaviour of the cyprid. Current investigators have shown that the former involves a prostaglandin which activates the embryos. Searching cyprids have been shown to be able to recognize their own and other species. Charles would have seen in this phenomenon a relevance both to survival and to the evolution of epizoic barnacles. Despite Charles' belief that his barnacle work would be “for ever unapplied” it has in fact been the foundation on which all studies of commercially important barnacle fouling have been based.     

God and natural selection: The Darwinian idea of design

Conclusion If we arrange in chronological order the various statements Darwin made about God, creation, design, plan, law, and so forth, that I have discussed, there emerges a picture of a consistent development in Darwin's religious views from the orthodoxy of his youth to the agnosticism of his later years. Numerous sources attest that at the beginning of the Beagle voyage Darwin was more or less orthodox in religion and science alike.⁷⁸ After he became a transmutationist early in 1837, he concluded that the doctrine of secondary causes must be extented even to the history of life and that after the first forms of life were created, there was no further need for divine intervention, except where man was concerned. Man's body, he thought, was produced by the process of transmutation, but he believed for a time that man's soul was superadded. By mid-1838 he had become convinced that nothing, after the creation of life, was due to miracles. God works only through laws, which are capable of producing every effect of evey kind which surrounds us. The existence of man, the idea of God in man's mind, and the harmony of the whole system were in his eyes prearranged goals of deterministic laws imposed by God. Such a conception excludes the miracles on which Christianity depends; but it is not possible to say whether Darwin's loss of Christian faith, which occurred at about this same time, preceded and made possible his materialism or was rather caused or hastened by it.⁷⁹ In the weeks after his reading of Malthus, Darwin's belief in a plan of creation gave way to the belief that God created matter and life and designed their laws, leaving the details, however, to the workings of chance. This remained his view until the 1860s.There is no exact parallel between this development of Darwin's religious views and the development of his ideas on evolution, but there is a general correspondence. When he believed in a plan of creation, Darwin's theory of transmutation did not depend on struggle or the selection of chance variations. Adaptation was, for him, an automatic response to environmental chance. From late 1838 to 1859 he believed in designed laws and chance, and this belief, too, has its parallel in his theory. The element of chance in natural selection meant that there could be no detailed plan,in which even man's idea of God would be a necessary outcome of nature's laws (man himself is not a necessary outcome of the working of natural selection).⁸⁰ But Darwin still believed nature was programmed to achieve certain general ends. We might say that he believed in a general, though not a special, teleology. Natural selection was for him a law to maximize utility, creating useful organs, retaining vestiges for future use. For many years it was a law designed to produce organisms perfectly adapted to their environments. Only later did Darwin come to doubt even this sort of design in nature.⁸¹ One way of describing the development of Darwin's evolutionary thought is to say that it shows a gradual abandoning of his theistic assumptions, so that by the late 1860s his theory was informed to a slighter extent by notions of purpose and design than it was in 1838 or 1844 or 1859.     

Darwin and the linguists: the coevolution of mind and language, part 2. The language-thought relationship

This paper examines Charles Darwin's idea that language-use and humanity's unique cognitive abilities reinforced each other's evolutionary emergence-an idea Darwin sketched in his early notebooks, set forth in his Descent of man (1871), and qualified in Descent's second (1874) edition. Darwin understood this coevolution process in essentially Lockean terms, based on John Locke's hints about the way language shapes thinking itself. Ironically, the linguist Friedrich Max Müller attacked Darwin's human descent theory by invoking a similar thesis, the German romantic notion of an identity between language and thought. Although Darwin avoided outright contradiction, when he came to defend himself against Müller's attacks, he undercut some of his own argumentation in favor of the coevolution idea. That is, he found it difficult to counter Müller's argument while also making a case for coevolution. Darwin's efforts in this area were further complicated by British and American writers who held a naturalistic view of speech origins yet still taught that language had been invented by fully evolved homo sapiens, thus denying coevolution.     

Darwin’s Sublime: The Contest Between Reason and Imagination in <Emphasis Type="Italic">On the Origin of Species</Emphasis>

Recent Darwin scholarship has provided grounds for recognising the Origin as a literary as well as a scientific achievement. While Darwin was an acute observer, a gifted experimentalist and indefatigable theorist, this essay argues that it was also crucial to his impact that the Origin transcended the putative divide between the scientific and the literary. Analysis of Darwin’s development as a writer between his journal-keeping on HMS Beagle and his construction of the Origin argues the latter draws on the pattern of the Romantic or Kantian sublime. The Origin repeatedly uses strategies which challenge the natural-theological appeal to the imagination in conceiving nature. Darwin’s sublime coaches the Origin’s readers into a position from which to envision nature that reduces and contains its otherwise overwhelming complexity. As such, it was Darwin’s literary achievement that enabled him to fashion a new ‘habit of looking at things in a given way’ that is the centrepiece of the scientific revolution bearing his name.     

From Charles Darwin's botanical country-house studies to modern plant biology

As a student of theology at Cambridge University, Charles Darwin (1809–1882) attended the lectures of the botanist John S. Henslow (1796–1861). This instruction provided the basis for his life-long interest in plants as well as the species question. This was a major reason why in his book On the Origin of Species , which was published 150 years ago, Darwin explained his metaphorical phrase 'struggle for life' with respect to animals and plants. In this article, we review Darwin's botanical work with reference to the following topics: the struggle for existence in the vegetable kingdom with respect to the phytochrome-mediated shade avoidance response; the biology of flowers and Darwin's plant–insect co-evolution hypothesis; climbing plants and the discovery of action potentials; the power of movement in plants and Darwin's conflict with the German plant physiologist Julius Sachs; and light perception by growing grass coleoptiles with reference to the phototropins. Finally, we describe the establishment of the scientific discipline of Plant Biology that took place in the USA 80 years ago, and define this area of research with respect to Darwin's work on botany and the physiology of higher plants.     

Darwin on Aristotle

Charles Darwin's famous 1882 letter, in response to a gift by his friend, William Ogle of Ogle's recent translation of Aristotle's Parts of Animals, in which Darwin remarks that his “two gods,” Linnaeus and Cuvier, were “mere school-boys to old Aristotle,” has been thought to be only an extravagantly worded gesture of politeness. However, a close examination of this and other Darwin letters, and of references to Aristotle in Darwin's earlier work, shows that the famous letter was written several weeks after a first, polite letter of thanks, and was carefully formulated and literally meant. Indeed, it reflected an authentic, and substantial, increase in Darwin's already high respect for Aristotle, as a result of a careful reading both of Ogle's Introduction and of more or less the portion of Ogle's translation which Darwin says he has read. Aristotle's promotion to the pantheon, as an examination of the basis for Darwin's admiration of Linnaeus and Cuvier suggests, was most likely the result specifically of Darwin's late discovery that the man he already knew as “one of the greatest ... observers that ever lived” (1879) was also the ancient equivalent both of the great modern systematist and of the great modern advocate of comparative functional explanation. It may also have reflected some real insight on Darwin's part into the teleological aspect of Aristotle's thought, indeed more insight than Ogle himself had achieved, as a portion of their correspondence reveals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Darwin and palaeontology: a re-evaluation of his interpretation of the fossil record

Charles Darwin's empirical research in palaeontology, especially on fossil invertebrates, has been relatively neglected as a source of insight into his thinking, other than to note that he viewed the fossil record as very incomplete. During the Beagle voyage, Darwin gained extensive experience with a wide diversity of fossil taxa, and he thought deeply about the nature of the fossil record. That record was, for him, a major source of evidence for large-scale transmutation, but much less so for natural selection or single lineages. Darwin's interpretation of the fossil record has been criticised for its focus on incompleteness, but the record as he knew it was extremely incomplete. He was compelled to address this in arguing for descent with modification, which was likely his primary goal. Darwin's gradualism has been both misrepresented and exaggerated, and has distracted us from the importance of the fossil record in his thinking, which should be viewed in the context of the multiple, sometimes competing demands of the multifaceted argument he presented in the Origin of Species.     

Experimenting with Transmutation: Darwin, the Beagle, and Evolution

Detailed analysis of Darwin’s scientific notes and other writings from the Beagle voyage reveals a focus on endemism and replacement of allied taxa in time and in space that began early in the journey. Though it is impossible to determine exactly when Darwin became a transmutationist, the evidence suggests that he was conversant with the transmutational ideas of Lamarck and others and testing (“experimenting” with) them—before he received a copy of Lyell’s Principles of Geology, vol. 2, in November 1832, in which Lyell describes and disputes Lamarck’s theory. To the two rhea species of Patagonia and the four mockingbird species of the Galapagos, we can now add the living Patagonian cavy (rodent) species, and its extinct putatively related species that Darwin collected at Monte Hermoso (Bahia Blanca) in the Fall of 1832, as a replacement pattern absolutely critical to the development of Darwin’s transmutational thinking. Darwin developed his first transmutational theory by adopting “Brocchi’s analogy” (Rudwick 2008)—i.e. that births and deaths of species are analogous to the births and deaths of individuals. Births and deaths of species, as of individuals, are thus explicable in terms of natural causes. Darwin explored these themes and the replacement of the extinct cavy by the modern species explicitly in his February 1835 essay (Darwin 1835a).

Darwin's biogeography

The year 2009 marks the 150th anniversary of the publication of Charles Darwin’s Origin of Species. This book was so influential that it is often considered to be the most important scientific work ever written. Many volumes have been published about the Origin and its lasting effects on religion and society, but few have examined its influence on biogeography. However, it was Darwin’s initial interest in comparing the natural history of different regions during the voyage of the Beagle that led him to propose natural selection as an evolutionary force. He had visited the Cape Verde Islands and saw the similarity of their biota to that of Africa, and then noted the South American relationships of the Galapagos fauna and flora. But the island plants and animals were different from their mainland relatives, and, in the Galapagos, each island appeared to have its own endemic forms. It was these biogeographical observations that were critical to Darwin’s formulation of a theory to account for them. His subsequent conclusions on the evolutionary importance of centres of origin and dispersal were generally well accepted for the next 100 years, until the advent of vicarianism, which began in the early 1970s. That vicarianist movement received an impetus from two sources: (1) the works of Leon Croizat, who did not believe that living organisms could disperse overseas by themselves; and (2) the development of plate tectonics and its causation of continental drift. Vicarianists believed that primitive species were originally widespread over the Earth’s surface but were rafted to different parts of the world by continental fractionation and movement. However, continental drift in the Mesozoic could not have involved contemporary species or genera as many vicarianists claimed. The development of phylogeography, beginning in the 1980s, and improved knowledge of the fossil record soon demonstrated that multitudes of living species, and even many genera and families, underwent long‐distance dispersal during the Cenozoic. This resulted in a decline of vicarianism and a vindication of Darwin’s conclusions on centres of origin and dispersal.     

Darwin the geologist: Between Lyell and von Buch

Upon returning from his voyage on the Beagle, Darwin prepared reports of his geological observations. Together, these reveal Darwin's approach to reasoning about geology. Darwin argued that successive terraces prove a very gradual elevation of the coast that lagoon islands show a reciprocal sinking of the oceanic floor. Hence, Darwin reinforced Lyell's uniformitarian, or steady state theory. Unlike lagoon islands, the movement of erratic boulders onto the plains is evidence of forces, which do not now exist. Darwin and Lyell attributed this movement to floating icebergs. However, mountain formation remained difficult for them to explain with reference to contemporary causes. Lyell discovered uplifts in Scandinavia, which resulted from epirogenesis, whereas mountain formation is an orogenesis, which involves both folding and uplift. Darwin was more impressed by uplift than by folds. However, when in Cordillera he saw strata overturned by masses of injected rock, proving successive periods of violence, Darwin took a position, which was closer to the plutonic theories of von Buch and Humboldt than it was to Lyell's uniformitarian views.     

Variation among families for characteristics of the adhesive plaque in the barnacle Balanus amphitrite

A quantitative genetics approach was used to examine variation in the characteristics of the adhesive plaque of the barnacle Balanus amphitrite Darwin attached to two silicone substrata. Barnacles settled on silicone polymer films occasionally form thick, soft adhesive plaques, in contrast to the thin, hard plaques characteristic of attachment to other surfaces. The proportion of barnacles producing a thick adhesive plaque was 0.31 for Veridian, a commercially available silicone fouling-release coating, and 0.18 for Silastic T-2, a silicone rubber used for mold-making. For both materials, significant variation among maternal families in the proportion of barnacles producing a thick adhesive plaque was observed, which suggests the presence of genetic variation, or maternal environmental effects, for this plaque characteristic. For the Veridian coating, barnacles expressing the thick adhesive plaque also exhibited significantly reduced tenacity. This represents the first reported case for potential genetic control of intraspecific phenotypic variation in the physical characteristics and tenacity of the adhesive of a fouling invertebrate.