Determining whether a homoplastic trait is the result of convergence or parallelism is central to many of the most important contemporary discussions in biology and philosophy: the relation between evolution and development, the importance of constraints on variation, and the role of contingency in evolution. In this article, I show that two recent attempts to draw a black-or-white distinction between convergence and parallelism fail, albeit for different reasons. Nevertheless, I argue that we should not be afraid of gray areas: a (...) clarified version of S. J. Gould's earlier account, based on a separation of underlying developmental mechanisms from the realized trait, still represents a useful approach. (shrink)

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)

Darwin's ideas on variation, heredity, and development differ significantly from twentieth-century views. First, Darwin held that environmental changes, acting either on the reproductive organs or the body, were necessary to generate variation. Second, heredity was a developmental, not a transmissional, process; variation was a change in the developmental process of change. An analysis of Darwin's elaboration and modification of these two positions from his early notebooks (1836-1844) to the last edition of the /Variation of Animals and Plants Under Domestication/ (1875) (...) complements previous Darwin scholarship on these issues. Included in this analysis is a description of the way Darwin employed the distinction between transmission and development, as well as the conceptual relationship he saw between heredity and variation. This paper is part of a larger project comparing commitments regarding variation during the latter half of the nineteenth century. (shrink)

The consensus among evolutionists seems to be that the morphological complexity of organisms increases in evolution, although almost no empirical evidence for such a trend exists. Most studies of complexity have been theoretical, and the few empirical studies have not, with the exception of certain recent ones, been especially rigorous; reviews are presented of both the theoretical and empirical literature. The paucity of evidence raises the question of what sustains the consensus, and a number of suggestions are offered, including the (...) possibility that certain cultural and/or perceptual biases are at work. In addition, a shift in emphasis from theoretical to empirical inquiry is recommended for the study of complexity, and guidelines for future empirical studies are proposed. (shrink)

Darwin provided us with a powerful theoretical framework to explain the evolution of living systems. Natural selection alone, however, has sometimes been seen as insufficient to explain the emergence of new levels of selection. The problem is one of “circularity” for evolutionary explanations: how to explain the origins of Darwinian properties without already invoking their presence at the level they emerge. That is, how does evolution by natural selection commence in the first place? Recent results in experimental evolution suggest a (...) way forward: Paul Rainey and his collaborators have shown that Darwinian properties could be exogenously imposed via what they call “ecological scaffolding.” This could solve the “black box” dilemma faced by Darwinian explanations of new levels of organization. Yet, despite “scaffolding” recently becoming a popular term in the study of cognition, culture, and evolution, the concept has suffered from vagueness and ambiguity. This article aims to show that scaffolding can be turned into a proper scientific concept able to do explanatory work within the context of the major evolutionary transitions. Doing so will allow us to once again extend the scope of the Darwinian model of evolution by natural selection. (shrink)

The role of paleontology in evolutionary biology between the publication of The Origin of Species in 1859 and the Evolutionary Synthesis of the 1940s is frequently described as mostly misguided failure. However, a significant number of American and British PDPS invertebrate paleontologists of this period did devote considerable attention to evolution, and their evolutionary theories and conclusions were a good deal more diverse and nuanced than previous histories have suggested. This paper brings into focus a number of important but underrecognized (...) aspects of the history of paleontology within the history of biology, including that PDPS paleontologists were not all as theoretically backward as they have been portrayed; that the post-Synthesis narrative of the history of evolution should be continually reevaluated, in part to decouple historical understanding from the agendas of authors who have used history to advance particular views of evolution; and that there is a much richer story to be told about the history of evolutionary biology in both the pre- and post-Synthesis eras. (shrink)

Did Darwin Write the Origin Backwards is Sober’s book that comes closest to history of science. Some reviews have expressed reservations about Sober’s inclination to subordinate historical accuracy to analytical clarity, and to contemporary discussions . My comments will be devoted to the kind of relationship that Sober entertains with history of science. I do not think that the author’s interest in history is superficial and instrumental.In the first section, I try to locate Sober’s book within ‘&HPS’ , a recent (...) initiative that gathers a growing number of people willing to promote a new regime of interaction between philosophy and history of science. I will suggest that Sober offers an interesting way of developing this approach. The more critical second section is devoted to Sober’s first chapter, bearing on the relationship between the two main tenets of Darwin’s argument in the Origin—descent with modif .. (shrink)

The word ‘environment’ has a history. Before the mid-nineteenth century, the idea of a singular, abstract entity—the organism—interacting with another singular, abstract entity—the environment—was virtually unknown. In this paper I trace how the idea of a plurality of external conditions or circumstances was replaced by the idea of a singular environment. The central figure behind this shift, at least in Anglo-American intellectual life, was the philosopher Herbert Spencer. I examine Spencer’s work from 1840 to 1855, demonstrating that he was exposed (...) to a variety of discussions of the ‘force of circumstances’ in this period, and was decisively influenced by the ideas of Auguste Comte in the years preceding the publication of Principles of psychology (1855). It is this latter work that popularized the word ‘environment’ and the corresponding idea of organism–environment interaction—an idea with important metaphysical and methodological implications. Spencer introduced into the English-speaking world one of our most enduring dichotomies: organism and environment. (shrink)

Analysis of the degree of intraspecific morphological polymorphism during the evolutionary history of trilobites using an informatic approach1 provides striking evidence of a long‐suspected but previously unsubstantiated pattern: degrees of polymorphism are markedly higher in phylogenetically basal, stratigraphically early species. This unequivocal pattern prompts further exploration of the relationship between microevolutionary variance and macroevolutionary history. It demonstrates that the ‘traditional’ fossil record of skeletonized organisms can provide unique insight into questions of major evolutionary interest. BioEssays 29:1081–1084, 2007. © 2007 Wiley (...) Periodicals, Inc. (shrink)