It is a challenge to explain how evolutionary altruism can evolve by the process of natural selection, since altruists in a group will be less fit than the selfish individuals in the same group who receive benefits but do not make donations of their own. Darwin proposed a theory of group selection to solve this puzzle. Very simply, even though altruists are less fit than selfish individuals within any single group, groups of altruists are more fit than groups of selfish (...) individuals. If a population is subdivided into many groups that vary in their altruistic tendencies, altruism will be favored at the level of selection among groups even as it is being disfavored at the level of selection among individuals within groups. Darwin’s scenario became the basis for a theoretical framework called multilevel selection theory. (shrink)

Taking its clues from Popperian philosophy of science, cladistics adopted a number of assumptions of the empiricist tradition. These include the identification of a dichotomy between observation reports and theoretical statements and its subsequent abandonment on the basis of the insight that all observation reports are theory-laden. The neglect of the ‘context of discovery’, which is the step of theory (hypothesis) generation. The emphasis on coherentism in the ‘context of justification’, which is the step of evaluation of the relative merits (...) of alternative theories. The appeal to a total evidence approach in phylogenetic inference. And finally, a silence about causation, which results in an instrumentalist approach to phylogeny reconstruction. This paper explores how these empiricist assumptions are embedded in phylogenetic systematics, and why these assumptions are problematic for cladists (or any taxonomists). (shrink)

Homology is a biological sameness relation that is purported to hold in the face of changes in form, composition, and function. In spite of the centrality and importance of homology, there is no consensus on how we should understand this concept. The two leading views of homology, the genealogical and developmental accounts, have significant shortcomings. We propose a new account, the hierarchical-dependency account of homology, which avoids these shortcomings. Furthermore, our account provides for continuity between special, general, and serial homology.

Biological individuality is a major topic of discussion in biology and philosophy of biology. Recently, several objections have been raised against traditional accounts of biological individuality, including the objections of monism, theory-centrism, ahistoricity, disciplinary isolationism, and the multiplication of conceptual uncertainties. In this introduction, I will examine the current philosophical landscape about biological individuality, and show how the contributions gathered in this special issue address these five objections. Overall, the aim of this issue is to offer a more diverse, unifying, (...) and scientifically informed conception of what a biological individual is. (shrink)

There is long-standing conflict between genealogical and developmental accounts of homology. This paper provides a general framework that shows that these accounts are compatible and clarifies precisely how they are related. According to this framework, understanding homology requires both an abstract genealogical account that unifies the application of the term to all types of characters used in phylogenetic systematics and locally enriched accounts that apply only to specific types of characters. The genealogical account serves this unifying role by relying on (...) abstract notions of ‘descent’ and ‘character’. As a result, it takes for granted the existence of such characters. This requires theoretical justification that is provided by enriched accounts, which incorporate the details by which characters are inherited. These enriched accounts apply to limited domains, providing the needed theoretical justification for recognizing characters within that domain. Though connected to the genealogical account of homology in this way, enriched accounts include phenomena that fall outside the scope of the genealogical account. They therefore overlap, but are not nested within, the genealogical account. Developmental accounts of homology are to be understood as enriched accounts of body part homology. Once they are seen in this light, the conflict with the genealogical account vanishes. It is only by understanding the fine conceptual structure undergirding the many uses of the term ‘homology’ that we can understand how these uses hang together. (shrink)

Novel varieties of interplay between humans, robots and software agents are on the rise. Computer-based artefacts are no longer mere tools but have become interaction partners. Distributed problem solving and social agency may be modelled by social computing systems based on multi-agent systems. MAS and agent-based modelling approaches focus on the simulation of complex interactions and relationships of human and/or non-human agents. MAS may be deployed both in virtual environments and cyber-physical systems. With regard to their impact on the physical (...) environment, such systems possess a virtual actuality in a testbed. They have a real actuality when they are employed in real time in order to govern processes in the natural world. Constellations of inter-agency and distributed agency materialize. This paper presents a multidimensional, gradual classification framework for individual and joint agency. Activity level, adaptivity, interaction and personification of others are essential dimensions. The framework allows constellations of distributed and collective agency in socio-technical systems to be analysed in detail. Scenarios where solely humans act can be compared to testbed simulations based on this classification scheme. (shrink)

The fitness of any evolutionary unit can be understood in terms of its two basic components: fecundity (reproduction) and viability (survival). Trade-offs between these fitness components drive the evolution of life-history traits in extant multicellular organisms. We argue that these trade-offs gain special significance during the transition from unicellular to multicellular life. In particular, the evolution of germ–soma specialization and the emergence of individuality at the cell group (or organism) level are also consequences of trade-offs between the two basic fitness (...) components, or so we argue using a multilevel selection approach. During the origin of multicellularity, we study how the group trade-offs between viability and fecundity are initially determined by the cell level trade-offs, but as the transition proceeds, the fitness trade-offs at the group level depart from those at the cell level. We predict that these trade-offs begin with concave curvature in single-celled organisms but become increasingly convex as group size increases in multicellular organisms. We argue that the increasingly convex curvature of the trade-off function is driven by the cost of reproduction which increases as group size increases. We consider aspects of the biology of the volvocine green algae – which contain both unicellular and multicellular members – to illustrate the principles and conclusions discussed. (shrink)

Philosophical discussions of biological classification have failed to recognise the central role of homology in the classification of biological parts and processes. One reason for this is a misunderstanding of the relationship between judgments of homology and the core explanatory theories of biology. The textbook characterisation of homology as identity by descent is commonly regarded as a definition. I suggest instead that it is one of several attempts to explain the phenomena of homology. Twenty years ago the ‘new experimentalist’ movement (...) in philosophy of science drew attention to the fact that many experimental phenomena have a ‘life of their own’: the conviction that they are real is not dependent on the theories used to characterise and explain them. I suggest that something similar can be true of descriptive phenomena, and that many homologies are phenomena of this kind. As a result the descriptive biology of form and function has a life of its own—a degree of epistemological independence from the theories that explain form and function. I also suggest that the two major ‘homology concepts’ in contemporary biology, usually seen as two competing definitions, are in reality complementary elements of the biological explanation of homology. (shrink)

There have been repeated attempts in the history of comparative biology to provide a mechanistic account of morphological homology. However, it is well-established that homologues can develop from diverse sets of developmental causes, appearing not to share any core causal architecture that underwrites character identity. We address this challenge with a new conceptual model of Character Identity Mechanisms. ChIMs are cohesive mechanisms with a recognizable causal profile that allows them to be traced through evolution as homologues despite having a diverse (...) etiological organization. Our model hypothesizes that anatomical units at different levels of organization—cell types, tissues, and organs—have level-specific ChIMs with different conserved parts, activities, and organization. Relying on a methodology of conceptual engineering, we show how the ChIM concept advances our understanding of the developmental basis of morphological characters, while forging an important link between comparative and mechanistic biology. (shrink)

Darwin’s classic ‘Origin of Species’ (Darwin 1859) described forces of selection acting upon individuals, but there remains a great deal of controversy about what exactly the status and definition of a biological individual is. Recently some authors have argued that the individual is dispensable – that an inability to pin it down is not problematic because little rests on it anyway. The aim of this paper is to show that there is a real problem of biological individuality, and an urgent (...) need to arbitrate over the current plethora of solutions to it. (shrink)

Different sources of data on the evolution of segmentation lead to very different conclusions. Molecular similarities in the developmental pathways generating a segmented body plan tend to suggest a segmented common ancestor for all bilaterally symmetrical animals. Data from paleontology and comparative morphology suggest that this is unlikely. A possible solution to this conundrum is that throughout evolution there was a parallel co‐option of gene regulatory networks that had conserved ancestral roles in determining body axes and in elongating the anterior‐posterior (...) axis. Inherent properties in some of these networks made them easily recruitable for generating repeated patterns and for determining segmental boundaries. Phyla where this process happened are among the most successful in the animal kingdom, as the modular nature of the segmental body organization allowed them to diverge and radiate into a bewildering array of variations on a common theme. (shrink)

By linking the concepts of homology and morphological organization to evolvability, this paper attempts to (1) bridge the gap between developmental and phylogenetic approaches to homology and to (2) show that developmental constraints and natural selection are compatible and in fact complementary. I conceive of a homologue as a unit of morphological evolvability, i.e., as a part of an organism that can exhibit heritable phenotypic variation independently of the organism’s other homologues. An account of homology therefore consists in explaining how (...) an organism’s developmental constitution results in different homologues/characters as units that can evolve independently of each other. The explanans of an account of homology is developmental, yet the very explanandum is an evolutionary phenomenon: evolvability in a character-by-character fashion, which manifests itself in phylogenetic patterns as recognized by phylogenetic approaches to homology. While developmental constraints and selection have often been viewed as antagonistic forces, I argue that both are complementary as they concern different parts of the evolutionary process. Developmental constraints, conceived of as the presence of the same set of homologues across phenotypic change, pertain to how heritable variation can be generated in the first place (evolvability), while natural selection operates subsequently on the produced variation. (shrink)

From mitochondria to meerkats, the natural world is full of spectacular examples of social behaviour. In the early 1960s W. D. Hamilton changed the way we think about how such behaviour evolves. He introduced three key innovations - now known as Hamilton's rule, kin selection, and inclusive fitness - and his pioneering work kick-started a research program now known as social evolution theory. This is a book about the philosophical foundations and future prospects of that program. [Note: only the Introduction (...) is available to download.]. (shrink)

Samir Okasha offers a critical study of agential thinking in biology, where evolved organisms are seen as agents pursuing a goal. He examines the justification for transposing concepts from rational humans to the biological world, and considers whether agential thinking is mere anthropomorphism or plays a more intellectual role in the science.

Primary sexual traits, those structures and processes directly involved in reproduction, are some of the most diverse, specialized, and bizarre in the animal kingdom. Moreover, reproductive traits are often species-specific, suggesting that they evolved very rapidly. This diversity, long the province of taxonomists, has recently attracted broader interest from evolutionary biologists, especially those interested in sexual selection and the evolution of reproductive strategies. Primary sexual characters were long assumed to be the product of natural selection, exclusively. A recent alternative suggests (...) that sexual selection explains much of the diversity of. (shrink)

The Limits of the Self, will be essential reading for anyone interested in the definition of biological individuality and the understanding of the immune system.

Drawing on recent advances in evolutionary biology, prominent scholars return to the question posed in a pathbreaking book: how evolution itself evolved.

The book presents a new way of understanding Darwinism and evolution by natural selection, combining work in biology, philosophy, and other fields.

This article began as a review of a conference, organized by Gerhard Schlosser, entitled “Modularity in Development and Evolution.” The conference was held at, and sponsored by, the Hanse Wissenschaftskolleg in Delmenhorst, Germany in May, 2000. The article subsequently metamorphosed into a literature and concept review as well as an analysis of the differences in current perspectives on modularity. Consequently, I refer to general aspects of the conference but do not review particular presentations. I divide modules into three kinds: structural, (...) developmental, and physiological. Every module fulfills none, one, or multiple functional roles. Two further orthogonal distinctions are important in this context: module-kinds versus module-variants-of-a-kind and reproducer versus nonreproducer modules. I review criteria for individuation of modules and mechanisms for the phylogenetic origin of modularity. I discuss conceptual and methodological differences between developmental and evolutionary biologists, in particular the difference between integration and competition perspectives on individualization and modular behavior. The variety in views regarding modularity presents challenges that require resolution in order to attain a comprehensive, rather than a piecemeal and fragmentary, evolutionary developmental biology. (shrink)

Comparative biology builds up systematic knowledge of the diversity of life, across evolutionary lineages and levels of organization, starting with evidence from a sparse sample of model organisms. In developmental biology, a key obstacle to the growth of comparative approaches is that the concept of homology is not very well defined for levels of organization that are intermediate between individual genes and morphological characters. In this paper, we investigate what it means for ontogenetic processes to be homologous, focusing specifically on (...) the examples of insect segmentation and vertebrate somitogenesis. These processes can be homologous without homology of the underlying genes or gene networks, since the latter can diverge over evolutionary time, while the dynamics of the process remain the same. Ontogenetic processes like these therefore constitute a dissociable level and distinctive unit of comparison requiring their own specific criteria of homology. In addition, such processes are typically complex and nonlinear, such that their rigorous description and comparison not only requires observation and experimentation, but also dynamical modeling. We propose six criteria of process homology, combining recognized indicators with novel ones derived from dynamical systems modeling. We show how these criteria apply to animal segmentation and other ontogenetic processes. We conclude by situating our proposed dynamical framework for homology of process in relation to similar research programs, such as process structuralism and developmental approaches to morphological homology. (shrink)