The Darwin of pangenesis

The Darwin of pangenesis is very much another Darwin. Pangenesis is Darwin's comprehensive theory of generation, his theory about all sexual and asexual modes of reproduction and growth. He never explicitly integrated pangenesis with his theory of natural selection. He first formulated pangenesis in the 1840s and integrated it with the physiology, including the cytology, of that era. It was, therefore, not consilient with the newer cytology of the 1860s when he published it in 1868. By reflecting on the role of pangenesis in Darwin's life and work, we can learn to take a wider view of his most general theorising about animal and plant life.     

Sexual selection: Another Darwinian process

Why was sexual selection so important to Darwin? And why was it de-emphasized by almost all of Darwin's followers until the second half of the 20th century? These two questions shed light on the complexity of the scientific tradition named “Darwinism”. Darwin's interest in sexual selection was almost as old as his discovery of the principle of natural selection. From the beginning, sexual selection was just another “natural means of selection”, although different from standard “natural selection” in its mechanism. But it took Darwin 30 years to fully develop his theory, from the early notebooks to the 1871 book The Descent of Man, and Selection in Relation to Sex. Although there is a remarkable continuity in his basic ideas about sexual selection, he emphasized increasingly the idea that sexual selection could oppose the action of natural selection and be non adaptive. In time, he also gave more weight to mate choice (especially female choice), giving explicit arguments in favor of psychological notions such as “choice” and “aesthetic sense”. But he also argued that there was no strict demarcation line between natural and sexual selection, a major difficulty of the theory from the beginning. Female choice was the main reason why Alfred Russel Wallace, the co-discoverer of the principle of natural selection, engaged in a major controversy with Darwin about sexual selection. Wallace was suspicious about sexual selection in general, trying to minimize it by all sorts of arguments. And he denied entirely the existence of female choice, because he thought that it was both unnecessary and an anthropomorphic notion. This had something to do with his spiritualist convictions, but also with his conception of natural selection as a sufficient principle for the evolutionary explanation of all biological phenomena (except for the origin of mind). This is why Wallace proposed to redefine Darwinism in a way that excluded Darwin's principle of sexual selection. The main result of the Darwin–Wallace controversy was that most Darwinian biologists avoided the subject of sexual selection until at least the 1950 s, Ronald Fisher being a major exception. This controversy still deserves attention from modern evolutionary biologists, because the modern approach inherits from both Darwin and Wallace. The modern approach tends to present sexual selection as a special aspect of the theory of natural selection, although it also recognizes the big difficulties resulting from the inevitable interaction between these two natural processes of selection. And contra Wallace, it considers mate choice as a major process that deserves a proper evolutionary treatment. The paper's conclusion explains why sexual selection can be taken as a test case for a proper assessment of “Darwinism” as a scientific tradition. Darwin's and Wallace's attitudes towards sexual selection reveal two different interpretations of the principle of natural selection: Wallace's had an environmentalist conception of natural selection, whereas Darwin was primarily sensitive to the element of competition involved in the intimate mechanism of any natural process of selection. Sexual selection, which can lack adaptive significance, reveals this exemplarily.     

Darwin on woman

In his 1871 book The Descent of Man, Darwin exposed the idea of sexual selection as a major principle of human evolution. His main hypothesis, which was already briefly presented in The Origin of Species, is that there exists, besides “natural selection”, another form of selection, milder in its effect, but no less efficient. This selection is operated by females to mate and reproduce with some partners that are gifted with more qualities than others, and more to their taste. At more evolved stages, sexual selection was exerted by men who became able to choose the women most attractive to their taste. However, Darwin insists, sexual selection in the human species is limited by a certain number of cultural practices. If Darwin's demonstration sometimes carried the prejudices of his times regarding gender differences he was the first who took into account the importance of sexual choices in his view on evolution, and who insisted on the evolutionary role of women at the dawn of humanity. Thus, he opened the space for a rich reflection, which after him was widely developed and discussed in anthropological and gender studies.     

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.     

Cross- and self-fertilization of plants

This essay considers Charles Darwin's late work, Cross- and Self-Fertilization of Plants, locating it in the overall context of Darwin's thought and ideas. It is shown how it is part of a long-term interest in the purpose of sexuality, and how it complements Darwin's earlier book on the fertilization of orchids. It is concluded, however, that Darwin had no full solution to his problem.     

The History and Reception of Charles Darwin’s Hypothesis of Pangenesis

This paper explores Charles Darwin’s hypothesis of pangenesis through a popular and professional reception history. First published in The Variation of Animals and Plants under Domestication (1868), pangenesis stated that inheritance can be explained by sub-cellular “gemmules” which aggregated in the sexual organs during intercourse. Pangenesis thereby accounted for the seemingly arbitrary absence and presence of traits in offspring while also clarifying some botanical and invertebrates’ limb regeneration abilities. I argue that critics largely interpreted Variation as an extension of On the Origin of Species by Means of Natural Selection (1859), while pangenesis was an extension of natural selection. Contrary to claims that pangenesis was divorced from natural selection by its reliance on the inheritance of acquired characters, pangenesis’s mid nineteenth-century reception suggests that Darwin’s hypothesis responded directly to selection’s critics. Using Variation’s several editions, periodical reviews, and personal correspondence I assess pangenesis popularly, professionally, and biographically to better understand Variation’s impact on 1860s and 70s British evolutionism and inheritance.     

Darwin's puzzling Expression

Charles Darwin's The Expression of the Emotions in Man and Animals (1872) is a very different kind of work from On the Origin of Species (1859). This “otherness” is most extreme in the character of the explanations that Darwin offers in the Expression. Far from promoting his theory of natural selection, the Expression barely mentions that theory, instead drawing on explanatory principles which recall less Darwinian than Lamarckian and structuralist biological theorizing. Over the years, historians have offered a range of solutions to the puzzle of why the Expression is so “non-Darwinian”. Close examination shows that none of these meets the case. However, recent research on Darwin's lifelong engagement with the controversies in his day over the unity of the human races makes possible a promising new solution. For Darwin, emotional expression served the cause of defending human unity precisely to the extent that natural selection theory did not apply.     

Darwin teleologist? Design in the Orchids

Focusing on the Orchids, this article aims at disentangling the concepts of teleology, design and natural theology. It refers to several contemporary critics of Darwin (Kölliker, Argyll, Royer, Candolle, Delpino) to challenge Huxley's interpretation that Darwin's system was “a deathblow” to teleology. The Orchids seem rather to be a “flank-movement” (Gray): it departs from the Romantic theories of transmutation and the “imaginary examples” of the Origin; it focuses on empirical data and on teleological structures. Although Darwin refers to natural selection, his readers mock him for his fascination for delicate morphological contrivances and co-adaptations – a sign that he was inescapably lured to finality. Some even suggested that his system was a “theodicy”. In the history of Darwinism, the Orchids reveal “another” quite unexpected and heterodox Darwin: freed from the hypothetical fancies of the Origin, and even suggesting a new kind of physico-theology.     

Separated at Birth: The Interlinked Origins of Darwin’s Unconscious Selection Concept and the Application of Sexual Selection to Race

This essay traces the interlinked origins of two concepts found in Charles Darwin’s writings: “unconscious selection,” and sexual selection as applied to humanity’s anatomical race distinctions. Unconscious selection constituted a significant elaboration of Darwin’s artificial selection analogy. As originally conceived in his theoretical notebooks, that analogy had focused exclusively on what Darwin later would call “methodical selection,” the calculated production of desired changes in domestic breeds. By contrast, unconscious selection produced its results unintentionally and at a much slower pace. Inspiration for this concept likely came from Darwin’s early reading of works on both animal breeding and physical ethnology. Texts in these fields described the slow and unplanned divergence of anatomical types, whether animal or human, under the guidance of contrasting ideals of physical perfection. These readings, it is argued, also led Darwin to his theory of sexual selection as applied to race, a theme he discussed mainly in his book The Descent of Man (1871). There Darwin described how the racial version of sexual selection operated on the same principle as unconscious selection. He thereby effectively reunited these kindred concepts.     

1 July 1858: what Wallace knew; what Lyell thought he knew; what both he and Hooker took on trust; and what Charles Darwin never told them

At the Linnean Society on 1 July 1858, Charles Lyell and Joseph Hooker, using only an extract from Charles Darwin's unpublished essay of 1844, and a copy of a recent letter to Asa Gray in Boston, argued successfully that Darwin understood how species originate long before a letter from Alfred Russel Wallace outlining his own version of the theory of evolution arrived at Darwin's home. That letter from Ternate in the Malay Archipelago, however, was not the first letter Darwin received from Wallace. This article will contend that two of the three letters Wallace sent Darwin between 10 October 1856 and 9 March 1858 arrived much earlier than Darwin recorded, thereby allowing him time to assess Wallace's ideas and claim an independent understanding of how the operation of divergence and extinction in the natural world leads strongly marked varieties to be identified as new species. By the time of the Linnean meeting Darwin's new ideas had filtered into his letters and ‘big’ species book, despite the absence of any independent evidence from the natural world to justify his constant insistence to have been guided only by inductive reasoning. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 725–736.     

Variation under domestication in plants: 1859 and today

Charles Darwin began The Origin of Species with a chapter entitled variation under domestication, which encapsulated decades of his research on a diverse array of animal and plant domesticated species. Variation in these species compared with that in their wild relatives, their origins and their selection by humans, formed a paradigm for his theory of the evolutionary origin of species by means of natural selection. This chapter, its subsequent expansion into a two-volume monograph, together with the rediscovery of Mendel''s laws, later became the foundation of scientific plant breeding. In the period up to the present, several advances in genetics (such as artificial mutation, polyploidy, adaptation and genetic markers) have amplified the discipline with concepts and questions, the seeds of which are in Darwin''s original words. Today, we are witnessing a flowering of genomic research into the process of domestication itself, particularly the specific major and minor genes involved. In one striking way, our view of domestic diversity contrasts with that in Darwin''s writing. He stressed the abundance of diversity and the diversifying power of artificial selection, whereas we are concerned about dwindling genetic diversity that attends modern agriculture and development. In this context, it is paramount to strive for a deeper understanding of how farmer selection including both deliberate selection and unconscious selection, might generate and retain diversity. This knowledge is essential for devising in situ conservation measures.     

PERSPECTIVE: INDIRECT MATE CHOICE,COMPETITION FOR MATES,AND COEVOLUTION OF THE SEXES

When Darwin first proposed the possibility of sexual selection, he identified two mechanisms, male competition for mates and female choice of mates. Extending this classification, we distinguish two forms of mate choice, direct and indirect. This distinction clarifies the relationship between Darwin's two mechanisms and, furthermore, indicates that the potential scope for sexual selection is much wider than thus far realized. Direct mate choice, the focus of most research on sexual selection in recent decades, requires discrimination between attributes of individuals of the opposite sex. Indirect mate choice includes all other behavior or morphology that restricts an individual's set of potential mates. Possibilities for indirect mate choice include advertisement of fertility or copulation, evasive behavior, aggregation or synchronization with other individuals of the same sex, and preferences for mating in particular locations. In each of these cases, indirect mate choice sets the conditions for competition among individuals of the opposite sex and increases the chances of mating with a successful competitor. Like direct mate choice, indirect mate choice produces assortative mating. As a consequence, the genetic correlation between alleles affecting indirect choice and those affecting success in competition for mates can produce self-accelerating evolution of these complementary features of the sexes. The broad possibilities for indirect mate choice indicate that sexual selection has more pervasive influences on the coevolution of male and female characteristics than previously realized.     

Darwin's sexual selection: Understanding his ideas in context

Darwin's writings need to be seen in their fullness, as opposed to quote-mining individual sentences without the context of his passages. Sometimes Darwin wrote at length, apparently favorably, about ideas that he subsequently undermined, replacing them with a more integrative view that reflected his own broad compass. Darwin understood that nature is not simple, that not all members of a group may have evolved under the same selective regime, and that variation of all kinds is fundamental to selection in its several forms. Sexual selection requires sexual dimorphism; it is not centred on variation within sexes but on selection for the ability to acquire mates. “Mutual sexual selection” was rejected by Darwin for every species except humans. Mating success is not a matter of mere numbers but of the transmission of the most attractive features to the opposite sex. The term “sexual selection” should only be used when one sex uses a feature not present in the other sex to attract mates or repel rivals for mates.     

Darwin as a student of behavior

In The Expression of the Emotions, Charles Darwin documents evolutionary continuity between animals and humans, emphasizing the universality of expressions in man. Most of the book addresses human behavior, and its influence on the study of animal behavior has been weak. The issue of natural selection is remarkably absent from this book, which relies on the inheritance of acquired characters rather than on a genuine Darwinian logic. Yet Konrad Lorenz considered Darwin to be a forerunner of behavioral biology. The reason was to be found in The Descent of Man and chapter VIII of The Origin of Species, where Darwin provides an explanation of behavior through selection, stating that the same mechanisms explaining morphological changes also account for gradual improvements in instincts. He assessed the accuracy of his evolutionary theory by directly studying animal behavior, hence laying the foundations of behavioral research for the next century.     

Darwin,the amphibians,and the natural selection

A critical review of Darwin's publications shows that he did not dissert much about amphibians, in comparison with the other tetrapods. However, in “A Naturalist's Voyage round the World”, Darwin described for the first time several amphibian species and was surprised by their peculiar way of life, terrestrial or euryhaline. These amphibian observations around the world led Darwin to discuss evolutionnary notions, like developmental heterochronies or evolving convergences, and later to illustrate his famous natural selection theory. This is confirmed, for example, by the publication of “On the Origin of Species” where Darwin ironically questioned creation theory, trying to explain the absence of amphibians on oceanic islands. Lamarck also considered amphibians as relevant material to illustrate his theory of acquired character heredity. These historical uses of lissamphibians as evolutionary models have been mostly realized before any amphibian fossil discovery, i.e. out of a palaeontological context.     

Menstrual cycle phase alters women's sexual preferences for composers of more complex music

Over 140 years ago Charles Darwin first argued that birdsong and human music, having no clear survival benefit, were obvious candidates for sexual selection. Whereas the first contention is now universally accepted, his theory that music is a product of sexual selection through mate choice has largely been neglected. Here, I provide the first, to my knowledge, empirical support for the sexual selection hypothesis of music evolution by showing that women have sexual preferences during peak conception times for men that are able to create more complex music. Two-alternative forced-choice experiments revealed that woman only preferred composers of more complex music as short-term sexual partners when conception risk was highest. No preferences were displayed when women chose which composer they would prefer as a long-term partner in a committed relationship, and control experiments failed to reveal an effect of conception risk on women''s preferences for visual artists. These results suggest that women may acquire genetic benefits for offspring by selecting musicians able to create more complex music as sexual partners, and provide compelling support for Darwin''s assertion ‘that musical notes and rhythm were first acquired by the male or female progenitors of mankind for the sake of charming the opposite sex’.     

Darwin's Galápagos finches in modern biology

One of the classic examples of adaptive radiation under natural selection is the evolution of 15 closely related species of Darwin''s finches (Passeriformes), whose primary diversity lies in the size and shape of their beaks. Since Charles Darwin and other members of the Beagle expedition collected these birds on the Galápagos Islands in 1835 and introduced them to science, they have been the subjects of intense research. Many biology textbooks use Darwin''s finches to illustrate a variety of topics of evolutionary theory, such as speciation, natural selection and niche partitioning. Today, as this Theme Issue illustrates, Darwin''s finches continue to be a very valuable source of biological discovery. Certain advantages of studying this group allow further breakthroughs in our understanding of changes in recent island biodiversity, mechanisms of speciation and hybridization, evolution of cognitive behaviours, principles of beak/jaw biomechanics as well as the underlying developmental genetic mechanisms in generating morphological diversity. Our objective was to bring together some of the key workers in the field of ecology and evolutionary biology who study Darwin''s finches or whose studies were inspired by research on Darwin''s finches. Insights provided by papers collected in this Theme Issue will be of interest to a wide audience.     

How Charles Darwin received Wallace's Ternate paper 15 days earlier than he claimed: a comment on van Wyhe and Rookmaaker (2012)

Van Wyhe and Rookmaaker (2012) postulate a set of events to support their claim that Wallace's ‘evolution’ letter, posted at Ternate in the Moluccas in the spring of 1858, arrived at Darwin's home on 18 June 1858. If their claim were to be proven, then evidence that Darwin probably received Wallace's letter 2 weeks earlier than he ever admitted would clearly be erroneous, and any charges that he plagiarized the ideas of Wallace from that letter would be shown to be wrong. Here, evidence against this interpretation is presented and it is argued that the letter did indeed arrive in the port of Southampton on 2 June 1858 and would have been at Darwin's home near London the following day. If this were true, then the 66 new pages of material on aspects of Divergence that Darwin entered into his ‘big’ species book in the weeks before admitting he had received the letter could be interpreted as an attempt to present Wallace's ideas as his own. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 472–477.     

Michael Ruse's Design for Living

The eminent historian and philosopher ofbiology, Michael Ruse, has writtenseveral books that explore the relationship ofevolutionary theory to its larger scientificand cultural setting. Among the questions hehas investigated are: Is evolution progressive? What is its epistemologicalstatus? Most recently, in Darwin and Design:Does Evolution have a Purpose?,Ruse has provided a history of the concept ofteleology in biological thinking, especially inevolutionary theorizing. In his book, he moves quickly from Plato and Aristotle to Kantand such British thinkers as Paley andWhewell. His main focus, though, is on Darwin'stheory and its subsequent fate. Ruserests his history on some shaky historical andphilosophic assumptions, particularly theunexamined notion that evolutionary theory isan abstract entity that isunproblematically realized in differenthistorical periods. He also assumes that Darwinconceived nature as if it were a Manchesterspinning loom – a clanking, dispassionatemachine. A more subtle analysis, which Ruseeschews, might discover that Darwin'sconception of nature owed a strong debt toGerman Romanticism and that he contrivedto infuse nature with moral and aestheticvalues, not to suck them from nature. Ruseproves he is a thinker to contend with, and this essayis quite contentious.     

Mort ou persistance du darwinisme ? Regard d’un épistémologue

The article examines why evolutionary biologists have been haunted by the question whether they are “Darwinian” or “non-Darwinian” ever since Darwin's Origin of species. Modern criticisms addressed to Darwinism are classified into two categories: those concerning Darwin's hypothesis of “descent with modification” and those addressed to the hypothesis of natural selection. In both cases, although the particular models that Darwin proposed for these two hypotheses have been significantly revised and expanded, Darwin's general framework has constrained and canalized evolutionary research, in the sense that it has settled an array of possible theoretical choices. Gould's changing attitudes regarding Darwinism is taken as a striking illustration of this interpretation.