The theory of evolution by natural selection is, perhaps, the crowning intellectual achievement of the biological sciences. There is, however, considerable debate about which entity or entities are selected and what it is that fits them for that role. This article aims to clarify what is at issue in these debates by identifying four distinct, though often confused, concerns and then identifying how the debates on what constitute the units of selection depend to a significant degree on which of these (...) four questions a thinker regards as central. (shrink)

Group selection is one acknowledged mechanism for the evolution of altruism. It is well known that for altruism to spread by natural selection, interactions must be correlated; that is, altruists must tend to associate with one another. But does group selection itself require correlated interactions? Two possible arguments for answering this question affirmatively are explored. The first is a bad argument, for it rests on a product/process confusion. The second is a more subtle argument, whose validity (or otherwise) turns on (...) issues concerning the meaning of multi-level selection and how it should be modelled. A cautious defence of the second argument is offered. Introduction Multi-level selection and the evolution of altruism Price's equation and multi-level selection Contextual analysis and multi-level selection The neighbour approach Recapitulation and conclusion. (shrink)

It has become customary in multilevel selection theory to use the same terms to denote both two explanatory goals and two explanatory means. This paper spells out some of the benefits that derive from avoiding this terminological conflation. I argue that keeping explanatory means and goals well apart allows us to see that, contrary to a popular recent idea, Price’s equation and contextual analysis—the statistical methods most extensively used for measuring the effects of certain evolutionary factors on the change in (...) the focal individual trait in multilevel selection scenarios—do not come with built-in notions of group selection and, therefore, the efficacy of these methods at analyzing various kinds of cases does not constitute a basis for deciding how group selection should best be defined. Moreover, contrary to another widely accepted idea, I argue that more than one type of group selection may serve as explanatory means when one’s goal is that of explaining the evolution of individual traits in multilevel selection scenarios and I spell out how this explanatory role should be understood. (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.

For a number of years, the debate in evolutionary biology over the ’levels of selection’ has attracted intense interest from philosophers of science. The main question concerns the level of the biological hierarchy at which natural selection occurs. Does selection act on organisms, genes, groups, colonies, demes, species, or some combination of these? According to traditional Darwinian theory the answer is the organism -- it is the differential survival and reproduction of individual organisms that drives the evolutionary process. But there (...) are alternative views too, including pluralist views which say that the choice between different levels of selection is often a matter of perspective, not empirical fact. (shrink)

Group-structured populations, of the kind prominent in discussions of multilevel selection, are contrasted with ‘neighbor-structured’ populations. I argue that it is a necessary condition on multilevel description of a selection process that there should be a nonarbitrary division of the population into equivalence classes (or an approximation to this situation). The discussion is focused via comparisons between two famous problem cases involving group structure (altruism and heterozygote advantage) and two neighbor-structured cases that resemble them. Conclusions are also drawn about the (...) role of correlated interaction in the evolution of altruism. 1 Introduction 2 Two Kinds of Population Structure 3 Objections and Replies 4 Particles on a Line 5 Conclusion Appendix: Neighborhoods and Selection CiteULike Connotea Del.icio.us What's this? (shrink)

Kin selection and multilevel selection are alternative approaches for studying the evolution of social behaviour, the relation between which has long been a source of controversy. Many recent theorists regard the two approaches as ultimately equivalent, on the grounds that gene frequency change can be correctly expressed using either. However, this shows only that the two are formally equivalent, not that they offer equally good causal representations of the evolutionary process. This article articulates the notion of an ‘adequate causal representation’ (...) using causal graphs, and then seeks to identify circumstances under which kin and multilevel selection do and do not satisfy the test of causal adequacy. 1 Introduction2 The KS and MLS Approaches2.1 The MLS decomposition2.2 The KS decomposition3 Equivalence and Causality4 Two Problem Cases4.1 The non-social trait case4.2 Genotypic selection with meiotic drive5 Casual Adequacy: A Graphical Approach5.1 The basic idea5.2 Graphs with individual and group variables5.3 Cases where KS is causally adequate5.4 Cases where MLS is causally adequate6 Discussion6.1 Relation to previous work. (shrink)

In "Some Criticism of the Contextual Approach, and a Few Proposals" in Biological Theory, Brian McLoone discusses some of the points about the contextual approach that I made in a recent paper. Besides offering a reply to McLoone’s comments on my paper, in this article I show why McLoone’s discussion of the two main frameworks for thinking about group selection—the contextual and the Price approach—is partly misguided. In particular, I show that one of McLoone’s main arguments against the contextual approach (...) is missing the target and that one of his (and Elliott Sober’s) arguments in defense of the Price approach is flawed. Criticizing these arguments will help me present an entirely different picture than McLoone’s of the current status of multilevel selection theory. More precisely, I argue that the idea that we are dealing with "multilevel selection" in the type of multigroup cases in which the focal units are the individuals (and their traits) has recently come under threat. Finally, I discuss the ways in which this idea might be salvaged by appealing either to the contextual or to the Price approach. (shrink)

In this article I explore some statistical difficulties confronting going conceptions of ‘group’ as understood in accounts of group selection. Most such theories require real groups but define the reality of groups in ways that make it impossible to test for their reality. There are alternatives, but they either require or invite a nominalism about groups that many theorists abjure.

In this paper, I identify two general positions with respect to the relationship between environment and natural selection. These positions consist in claiming that selective claims need and, respectively, need not be relativized to homogenous environments. I then show that adopting one or the other position makes a difference with respect to the way in which the effects of selection are to be measured in certain cases in which the focal population is distributed over heterogeneous environments. Moreover, I show that (...) these two positions lead to two different interpretations—the Pricean and contextualist ones—of a type of selection scenarios in which multiple groups varying in properties affect the change in the metapopulation mean of individual-level traits. Showing that these two interpretations stem from different attitudes towards environmental homogeneity allows me to argue: that, unlike the Pricean interpretation, the contextualist interpretation can only claim that drift or selection is responsible for the change in frequency of the focal trait in a given metapopulation if details about whether or not group formation is random are specified; that the traditional main objection against the Pricean interpretation—consisting in arguing that the latter takes certain side-effects of individual selection to be effects of group selection—is unconvincing. This leads me to suggest that the ongoing debate about which of the two interpretations is preferable should concentrate on different issues than previously thought. (shrink)

The contextual approach is a prominent framework for thinking about group selection. Here, I highlight ambiguity about what the contextual approach is. Then, I discuss problematic entailments the contextual approach has for what processes count as group selection—entailments more troublesome than typically noted. However, Sober and Wilson’s version of the Price approach, which is the main alternative to the contextual approach, is problematic too: it leads to an underappreciated paradox called the vanishing selection problem and thereby generates the wrong qualitative (...) account of whether group selection is occurring in a certain family of cases. In response, I develop an account of group selection that can deal with the counterexamples to both the contextual approach and the Price approach. I then discuss the role that contextual analysis can continue to play in the discussion of individual fitness and metapopulation evolution. (shrink)

This paper argues that the contextual approach to natural selection does not offer an estimation of the contributions of individual and group selection to evolutionary change in multi-level selection scenarios, and that this is so because the term “group selection”, as defined by the contextual approach, does not refer to a process taking place at the group level. In the contextual analysis framework, this term simply denotes an evolutionary change that takes place due to the fact that, overall, individual types (...) do not share similar contexts or environments, and the only way to claim that such an evolutionary change is a result of selection is by admitting that “group selection” is in fact a kind of frequency-dependent selection, i.e. a selection process taking place at the individual level. Therefore, under the names “individual selection” and “group selection”, the contextual approach actually isolates two aspects of the relation between individual types and their environment, and not two distinct levels of selection. (shrink)