August Weismann is famous for having argued against the inheritance of acquired characters. However, an analysis of his work indicates that Weismann always held that changes in external conditions, acting during development, were the necessary causes of variation in the hereditary material. For much of his career he held that acquired germ-plasm variation was inherited. An irony, which is in tension with much of the standard twentieth-century history of biology, thus exists – Weismann was not a Weismannian. I distinguish three (...) claims regarding the germ-plasm: (1) its continuity, (2) its morphological sequestration, and (3) its variational sequestration. With respect to changes in Weismann’s views on the cause of variation, I divide his career into four stages. For each stage I analyze his beliefs on the relative importance of changes in external conditions and sexual reproduction as causes of variation in the hereditary material. Weismann believed, and Weismannism denies, that variation, heredity, and development were deeply intertwined processes. This article is part of a larger project comparing commitments regarding variation during the latter half of the nineteenth century. (shrink)

Throughout the history of evolutionary theory a number of scientists have argued that evolution proceeds along a limited number of definite trajectories, a concept and group of theories known as “orthogenesis”. Beginning in the 1880s, influential evolutionists including Theodor Eimer, Edward Drinker Cope, and Leo Berg argued that a fully causal explanation of evolution must take into account the origin and nature of variation, an idea that implied orthogenesis in their views. This paper argues that these orthogenesis developed theories that (...) were more than highly technical and theoretically dubious hypotheses accessible only to elite specialists, as certain histories of these ideas might suggest. Some orthogenesists made their case to a non-specialist audience to gain support for their ideas in the face of widespread controversy over evolutionary theory. Through a case study analysis of three major books by Eimer, Cope, and Berg, this paper contends that they sought to re-orient the central tenets of the science of evolution to include the causal impact of variation on evolutionary outcomes. These orthogenesists developed novel and synthetic evolutionary theories in a publishing platform suited for non-specialist audiences in an effort to impact the debates over evolutionary causation prevalent in the late-19th and early 20th centuries. (shrink)

Raphael Meldola (1849-1915), an industrial chemist and keen naturalist, under the influence of Darwin, brought new German studies on evolution by natural selection that appeared in the 1870s to the attention of the British scientific community. Meldola's special interest was in mimicry among butterflies; through this he became a prominent neo-Darwinian. His wide-ranging achievements in science led to appointments as president of important professional scientific societies, and of a local club of like-minded amateurs, particularly field naturalists. This is an account (...) of Meldola's early scientific connections and studies related to entomology and natural selection, his contributions to the study of mimicry, and his promotion in the mid-1890s of a more theory driven approach among entomologists. (shrink)

Prior to August Weismann’s 1889 germ-plasm theory, social reformers believed that humans could inherit the effects of a salubrious environment and, by passing environmentally-induced modifications to their offspring, achieve continuous progress. Weismann’s theory disrupted this logic and caused many to fear that they had little control over human development. As numerous historians have observed, this contributed to the birth of the eugenics movement. However, through an examination of the work of social scientists Lester Frank Ward, Richard T. Ely, Amos Griswold (...) Warner, James Mark Baldwin, Simon Nelson Patten, Alfred Kroeber, Walter Robinson Smith, and Luther Lee Bernard, I demonstrate that Weismann’s ideas also prompted scholars to create of theories of human progress in which the social environment had a central role and biological heredity had a diminished one. Furthermore, in creating a new theory of social progress based on a concept called “social heredity,” the thinkers surveyed in this article separated biological and social thought and asserted the independence of the American social sciences. I argue that this represents an important moment in the maturation of the human sciences, and I suggest that the germ-plasm theory of heredity deserves a larger place in histories of the development of the American social scientific disciplines. (shrink)

Rudolf Leuckart's 1851 pamphlet Ueber den Polymorphismus der Individuen (On the polymorphism of individuals) stood at the heart of naturalists' discussions on biological individuals, parts and wholes in mid-nineteenth-century Britain and Europe. Our analysis, which accompanies the first translation of this pamphlet into English, situates Leuckart's contribution to these discussions in two ways. First, we present it as part of a complex conceptual knot involving not only individuality and the understanding of compound organisms, but also the alternation of generations, the (...) division of labor in nature, and the possibility of finding general laws of the organic world. Leuckart's pamphlet is important as a novel attempt to give order to the strands of this knot. It also solved a set of key biological problems in a way that avoided some of the drawbacks of an earlier teleological tradition. Second, we situate the pamphlet within a longer trajectory of inquiry into part-whole relations in biology from the mid-eighteenth century to the present. We argue that biological individuality, along with the problem-complexes with which it engaged, was as central a problem to naturalists before 1859 as evolution, and that Leuckart's contributions to it left a long legacy that persisted well into the twentieth century. As biologists' interests in part-whole relations are once again on the upswing, the longue durée of this problem merits renewed consideration. (shrink)

Rudolf Leuckart’s 1851 pamphlet Ueber den Polymorphismus der Individuen stood at the heart of naturalists’ discussions on biological individuals, parts and wholes in mid-nineteenth-century Britain and Europe. Our analysis, which accompanies the first translation of this pamphlet into English, situates Leuckart’s contribution to these discussions in two ways. First, we present it as part of a complex conceptual knot involving not only individuality and the understanding of compound organisms, but also the alternation of generations, the division of labor in nature, (...) and the possibility of finding general laws of the organic world. Leuckart’s pamphlet is important as a novel attempt to give order to the strands of this knot. It also solved a set of key biological problems in a way that avoided some of the drawbacks of an earlier teleological tradition. Second, we situate the pamphlet within a longer trajectory of inquiry into part-whole relations in biology from the mid-eighteenth century to the present. We argue that biological individuality, along with the problem-complexes with which it engaged, was as central a problem to naturalists before 1859 as evolution, and that Leuckart’s contributions to it left a long legacy that persisted well into the twentieth century. As biologists’ interests in part-whole relations are once again on the upswing, the longue durée of this problem merits renewed consideration. (shrink)

Biological development is about history, the history of an individual through time. Historically, the dominant epigenetic tradition has seen the developmental process as an unfolding of potential or in terms of the emergence of new organization that becomes an individual organism over time. The concept of development has included differentiation, growth, and morphogenesis; since the mid-nineteenth century, it has been seen in terms of cell division. Along the way have come explorations of such issues as the extent to which development (...) is driven by hereditary determination rather than flexible regulation in response to changing conditions. Some researchers have focused specifically on examining the capacity for regeneration in response to injury or loss, or on the extent to which parts are self-organizing individually rather than determined segments of a whole. This paper introduces the historical study of development. (shrink)

In the period 1875-1920, a debate about the generality and applicability of evolutionary theory to all organisms was motivated by work on unicellular ciliates like Paramecium because of their peculiar nuclear dualism and life cycles. The French cytologist Emile Maupas and the German zoologist August Weismann argued in the 1880s about the evolutionary origins and functions of sex (which in the ciliates is not linked to reproduction), and death (which appeared to be the inevitable fate of lineages denied sexual conjugation), (...) an argument rooted in the question of whether the ciliates and their processes where homologous to other cellular organisms. In the beginning of the twentieth century, this question of homology came to be less important as the ciliates were used by the British protozoologist Clifford Dobell and the American zoologist Herbert Spencer Jennings to study evolutionary processes in general rather than problems of development and cytology. For them, homology mattered less than analogy. This story illustrates two partially distinct problems in evolutionary biology: first, the question of whether all living things have common features and origins; and second, whether their history and current nature can be described by identical mechanisms. Where Maupas (contra Weismann) made the ciliates qualitatively the same as all other organisms in order to create a cohesive evolutionary theory for biology, Jennings and Dobell made them qualitatively different in order to achieve the same end. (shrink)

In 1920, Eugen Steinach and Paul Kammerer reported experiments showing that exposure to high temperatures altered the structure of the gonad and produced hyper-sexuality in "heat rats," presumably as a result of the increased production of sex hormones. Using Steinach's evidence that the gonad is a double gland with distinct sexual and generative functions, they used their findings to explain "racial" differences in the sexuality of indigenous tropical peoples and Europeans. The authors also reported that heat induced anatomical changes in (...) the interstitial cells of the gonad were inherited by the heat rats' descendants. Kammerer used this finding to link endocrinology to his long-standing interest in the inheritance of acquired characteristics. The heat rats supported his hypothesis that the interstitial cells of the double gland were the mechanism of somatic induction in the inheritance of acquired characteristics. The Steinach-Kammerer collaboration, Kammerer's use of Steinach's "puberty gland" to explain somatic induction, and his endocrine analysis of symbiosis reveal Paul Kammerer's late career attempt to integrate endocrinology and genetics with the political ideals of Austrian socialism. With them he developed a bioethics that challenged the growing reliance on race in eugenics and instead promoted cooperation over competition in evolution. I relate his attempt to the controversies surrounding the interstitial cells, to the status of extra-nuclear theories of heredity, and to Kammerer's commitment to Austromarxist social reforms during the interwar period. (shrink)

This paper has three principal aims: first, through a detailed analysis of the hypotheses and assumptions underlying Weismann’s and Morgan’s disagreement on the nature of animal regeneration, it seeks to readdress the imbalance in coverage of their discussion, providing, at the same time, a fascinating case-study for those interested in general issues related to controversies in science. Second, contrary to Morgan’s beliefs according to which Weismann employed a speculative and unempirical method of scientific investigation, the article shows that Weismann performed (...) experiments, made observations and proposed ‘undogmatic’ theories open to refutation. Third, through the reconstruction of Weismann’s and Morgan’s disagreement, this study illustrates how biology, during the very late nineteenth and early twentieth centuries, was undergoing important changes. I argue that this controversy clearly and convincingly demonstrates how some important epistemic assumptions became increasingly problematic for some members of the younger generations of biologists. At the end of my discussion I will also argue that Weismann and Morgan both had strong well-grounded arguments supporting their conclusions; for this reason I suggest a few factors (“taken-for-granted” beliefs or assumptions) that could explain why their disagreement was doomed to remain unresolved. In particular, I will analyze their diverse explicative interests, their different theoretical concerns and their distinct use of the available evidence. (shrink)

In this essay I discuss the contents and the context of Italian zoologist and entomologist Carlo Emery’s discussion of the germ-plasm theory. August Weismann considered him one of his very few creditable supporters, and encouraged him to publish his theoretical reflections. In his Gedanken zur Descendenz- und Vererbungstheorie, which appeared between 1893 and 1903 as a series of five essays in the journal Biologisches Zentralblatt, Emery developed a very personal account, applying the concept of determinants to problems like atavism, sexual (...) dimorphism, speciation, geographical isolation, transmission of characters, and putting forward, as early as 1903, the idea of a genetic program. (shrink)

Discussions of the implications of sexual reproduction have appeared throughout the history of evolutionary biology, from Darwin to Weismann, Fisher, Muller, Maynard Smith, and Williams. The latest of these appearances highlighted an evolutionary paradox that had previously been overlooked. In many animal and plant species reproduction is obligately sexual and also half the offspring are male, yet the males contribute nothing but genes to reproduction. If asexual mutants of such a species were to produce as many asexual offspring on average (...) as sexual females in that species produce daughters and sons, the growth rate of their population would be twice as large. Whereas half the offspring of sexual females are noncontributory males, all the offspring of such an asexual mutant would contribute to growth rate. Nevertheless, sexual reproduction prevails in most species and is not lost evolutionarily. (shrink)

In the years of the post-Darwinian debate, many American naturalists invoked the name of Lamarck to signal their belief in a purposive and anti-Darwinian view of evolution. Yet Weismann’s theory of germ-plasm continuity undermined the shared tenet of the neo-Lamarckian theories as well as the idea of the interchangeability between biological and social heredity. Edward Drinker Cope, the leader of the so-called “American School,” defended his neo-Lamarckian philosophy against every attempt to redefine the relationship between behavior, development, and heredity beyond (...) the epigenetic model of inheritance. This paper explores Cope’s late-career defense of neo-Lamarckism. Particular attention is dedicated to the debate he had with James Mark Baldwin before the publication of Baldwin’s own “A New Factor in Evolution”. I argue that Cope’s criticism was partly due to the fact that Baldwin’s theory of social heredity threatened Cope’s biologistic stance, as well as his attempt to preserve design in nature. This theoretical attitude had a remarkable impact on Baldwin’s arguments for the theory of organic selection. (shrink)