Does natural selection act primarily on individual organisms, on groups, on genes, or on whole species? The question of levels of selection - on which biologists and philosophers have long disagreed - is central to evolutionary theory and to the philosophy of biology. Samir Okasha's comprehensive analysis gives a clear account of the philosophical issues at stake in the current debate.

The authors demonstrate that unselfish behavior is in fact an important feature of both biological and human nature. Their book provides a panoramic view of altruism throughout the animal kingdom--from self-sacrificing parasites to the human capacity for selflessness--even as it explains the evolutionary sense of such behavior.

We review Evolution and the Levels of Selection by Samir Okasha. This important book provides a cohesive philosophical framework for understanding levels-of-selections problems in biology. Concerning evolutionary transitions, Okasha proposes that three stages characterize the shift from a lower level of selection to a higher one. We discuss the application of Okasha’s three-stage concept to the evolutionary transition from unicellularity to multicellularity in the volvocine green algae. Okasha’s concepts are a provocative step towards a more general understanding of the major (...) evolutionary transitions; however, the application of certain ideas to the volvocine model system is not straightforward. (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)

It is a common complaint that antireductionist arguments are primarily negative. Here I describe an alternative nonreductionist epistemology based on considerations taken from multidisciplinary research in biology. The core of this framework consists in seeing investigation as coordinated around sets of problems (problem agendas) that have associated criteria of explanatory adequacy. These ideas are developed in a case study, the explanation of evolutionary innovations and novelties, which demonstrates the applicability and fruitfulness of this nonreductionist epistemological perspective. This account also bears (...) on questions of conceptual change and theory structure in philosophy of science. †To contact the author, please write to: Department of Philosophy, University of Minnesota, 831 Heller Hall, 271 19th Ave. S., Minneapolis, MN 55455; e‐mail: [email protected]. (shrink)

Formal methods developed for modeling levels of selection problems have recently been applied to the investigation of major evolutionary transitions. We discuss two new tools of this kind. First, the ‘near-variant test’ can be used to compare the causal adequacy of predictively equivalent representations. Second, ‘state-variable gestalt-switching’ can be used to gain a useful dual perspective on evolutionary processes that involve both higher and lower level populations.

Both biologists and philosophers often make use of simple verbal formulations of necessary and sufficient conditions for evolution by natural selection (ENS). Such summaries go back to Darwin's Origin of Species (especially the "Recapitulation"), but recent ones are more compact.1 Perhaps the most commonly cited formulation is due to Lewontin.2 These summaries tend to have three or four conditions, where the core requirement is a combination of variation, heredity, and fitness differences. The summaries are employed in several ways. First, they (...) are often used in pedagogical contexts, and in showing the coherence of evolutionary theory in response to attacks from outside biology. Second, they are important in discussions of extensions of evolutionary principles to new domains, such as cultural change. The summaries also have intrinsic scientific and philosophical interest as attempts to capture some core principles of evolutionary theory in a highly concise way. Despite their prominence, both the proper formulation and status of these summaries are unclear. Standard formulations are subject to counterexamples, and their relations to formal models of evolutionary change are not straightforward. Here I look closely at these verbal summaries, and at how they relate to formal models. Are the summaries merely rough approximations that have no theoretical role of their own? Perhaps they could operate as theoretical statements in Darwin's time, but have now been superseded by more exact treatments. (shrink)

The commentaries by Dennett, Sterelny, and Queller on Darwinian Populations and Natural Selection (DPNS) are so constructive that they make it possible to extend and improve the book’s framework in several ways. My replies will focus on points of disagreement, and I will pick a small number of themes and develop them in detail. The three replies below are mostly self-contained, except that all my comments about genes, discussed by all three critics, are in the reply to Queller. Agential views (...) of evolution, discussed by Queller and Dennett, are addressed in my reply to Dennett. (shrink)

This paper examines David Hull’s and Peter Godfrey-Smith’s accounts of biological individuality using the case of biofilms. Biofilms fail standard criteria for individuality, such as having reproductive bottlenecks and forming parent-offspring lineages. Nevertheless, biofilms are good candidates for individuals. The nature of biofilms shows that Godfrey-Smith’s account of individuality, with its reliance on reproduction, is too restrictive. Hull’s interactor notion of individuality better captures biofilms, and we argue that it offers a better account of biological individuality. However, Hull’s notion of (...) interactor needs more precision. We suggest some ways to make Hull’s notion of interactor and his account of individuality more precise. Generally, we maintain that biofilms are a good test case for theories of individuality, and a careful examination of biofilms furthers our understanding of biological individuality. (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)

Biological theory demands a clear organism concept, but at present biologists cannot agree on one. They know that counting particular units, and not counting others, allows them to generate explanatory and predictive descriptions of evolutionary processes. Yet they lack a unified theory telling them which units to count. In this paper, I offer a novel account of biological individuality, which reconciles conflicting definitions of ‘organism’ by interpreting them as describing alternative realisers of a common functional role, and then defines individual (...) organisms as essentially possessing some mechanisms that play this role. (shrink)

This chapter develops the idea that the germ-soma split and the suppression of individual fitness differences within the corporate entity are not always essential steps in the evolution of corporate individuals. It illustrates some consequences for multilevel selection theory. It presents evidence that genetic heterogeneity may not always be a barrier to successful functioning as a higher-level individual. This chapter shows that levels-of-selection theorists are wrong to assume that the central problem in transitions is always that of minimizing within-group competition. (...) Evidence of intralevel conflict does not qualify as evidence against the existence of a higher level of selection. (shrink)

The problem of plant individuality is something which has vexed botanists throughout the ages, with fashion swinging back and forth from treating plants as communities of individuals (Darwin 1800 ; Braun and Stone 1853 ; Münch 1938 ) to treating them as organisms in their own right, and although the latter view has dominated mainstream thought most recently (Harper 1977 ; Cook 1985 ; Ariew and Lewontin 2004 ), a lively debate conducted mostly in Scandinavian journals proves that the issues (...) are far from being resolved (Tuomi and Vuorisalo 1989b ; Fagerström 1992 ; Pan and Price 2001 ). In this paper I settle the matter once and for all, by showing which elements of each side are correct. (shrink)

Among mycologists, questions persist about what entities should be treated as the fundamental units of fungal populations. This article articulates a coherent view about populations of heterokaryotic fungi and the individuals that comprise them. Using Godfrey-Smith’s minimal concept of a Darwinian population, I argue that entities at two levels of the biological hierarchy satisfy the minimal concept in heterokaryotic fungi: mycelia and nuclei. I provide a preliminary answer to the question of how to understand the relation between these two populations. (...) This article contributes to discussions about the nature of biological individuality, organismality, and evolutionary transitions. (shrink)

The notion that natural selection is a process of fitness maximization gets a bad press in population genetics, yet in other areas of biology the view that organisms behave as if attempting to maximize their fitness remains widespread. Here I critically appraise the prospects for reconciliation. I first distinguish four varieties of fitness maximization. I then examine two recent developments that may appear to vindicate at least one of these varieties. The first is the ‘new’ interpretation of Fisher's fundamental theorem (...) of natural selection, on which the theorem is exactly true for any evolving population that satisfies some minimal assumptions. The second is the Formal Darwinism project, which forges links between gene frequency change and optimal strategy choice. In both cases, I argue that the results fail to establish a biologically significant maximization principle. I conclude that it may be a mistake to look for universal maximization principles justified by theory alone. A more promising approach may be to find maximization principles that apply conditionally and to show that the conditions were satisfied in the evolution of particular traits. (shrink)

In this paper we explore the organizational conditions underlying the emergence of organisms at the multicellular level. More specifically, we shall propose a general theoretical scheme according to which a multicellular organism is an ensemble of cells that effectively regulates its own development through collective mechanisms of control of cell differentiation and cell division processes. This theoretical result derives from the detailed study of the ontogenetic development of three multicellular systems and, in particular, of their corresponding cell-to-cell signaling networks. The (...) case study supports our claim that a specific type of functional integration among the cells of a multicellular ensemble , is required for it to qualify as a proper organism. Finally, we argue why a multicellular system exhibiting this type of functionally differentiated and integrated developmental organization becomes a self-determining collective entity and, therefore, should be considered as a second-order autonomous system. (shrink)

We argue that the transition from unicellular to multicellular systems raises important conceptual challenges for understanding agency. We compare several MC systems displaying different forms of collective behavior, and we analyze whether these actions can be considered organismically integrated and attributable to the whole. We distinguish between a ‘constitutive’ and an ‘interactive’ dimension of organizational complexity, and we argue that MC agency requires a radical entanglement between the related processes which we call “the constitutive-interactive closure principle”. We explain in detail (...) that this is not possible without a regulatory center functionally integrating the two dimensions, and we also argue that, in turn, this type of regulation would not be possible without a special type of organization between the cells required for the development and maintenance of systems capable of integrated behavior. (shrink)

Philosophers of evolutionary biology favor the so-called etiological concept of function according to which the function of a trait is its evolutionary purpose, defined as the effect for which that trait was favored by natural selection. We term this the selected effect (SE) analysis of function. An alternative account of function was introduced by Robert Cummins in a non-evolutionary and non-purposive context. Cummins''s account has received attention but little support from philosophers of biology. This paper will show that a similar (...) non-purposive concept of function, which we term causal role (CR) function, is crucial to certain research programs in evolutionary biology, and that philosophical criticisms of Cummins''s concept are ineffective in this scientific context. Specifically, we demonstrate that CR functions are a vital and ineliminable part of research in comparative and functional anatomy, and that biological categories used by anatomists are not defined by the application of SE functional analysis. Causal role functions are non-historically defined, but may themselves be used in an historical analysis. Furthermore, we show that a philosophical insistence on the primary of SE functions places practicing biologists in an untenable position, as such functions can rarely be demonstrated (in contrast to CR functions). Biologists who study the form and function of organismal design recognize that it is virtually impossible to identify the past action of selection on any particular structure retrospectively, a requirement for recognizing SE functions. (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.

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

Genes and the Agents of Life undertakes to rethink the place of the individual in the biological sciences, drawing parallels with the cognitive and social sciences. Genes, organisms, and species are all agents of life but how are each of these conceptualized within genetics, developmental biology, evolutionary biology, and systematics? The 2005 book includes highly accessible discussions of genetic encoding, species and natural kinds, and pluralism above the levels of selection, drawing on work from across the biological sciences. The book (...) is a companion to the author's Boundaries of the Mind (2004), also available from Cambridge, where the focus is the cognitive sciences. The book will appeal to a broad range of professionals and students in philosophy, biology, and the history of science. You can download the table of contents and the first chapter here. (shrink)

In this chapter I lay out a notion of philosophical naturalism that aligns with pragmatism. It is developed and illustrated by a presentation of my views on natural kinds and my theory of concepts. Both accounts reflect a methodological naturalism and are defended not by way of metaphysical considerations, but in terms of their philosophical fruitfulness. A core theme is that the epistemic interests of scientists have to be taken into account by any naturalistic philosophy of science in general, and (...) any account of natural kinds and scientific concepts in particular. I conclude with general methodological remarks on how to develop and defend philosophical notions without using intuitions. (shrink)

Individuals are a prominent part of the biological world. Although biologists and philosophers of biology draw freely on the concept of an individual in articulating both widely accepted and more controversial claims, there has been little explicit work devoted to the biological notion of an individual itself. How should we think about biological individuals? What are the roles that biological individuals play in processes such as natural selection (are genes and groups also units of selection?), speciation (are species individuals?), and (...) organismic development (do genomes code for organisms)? Much of our discussion here will focus on organisms as a central kind of biological individual, and that discussion will raise broader questions about the nature of the biological world, for example, about its complexity, its organization, and its relation to human thought. (shrink)