Samir Okasha

Altruism, Group Selection and Correlated Interaction

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. 1. Introduction2. Multi-level selection and the evolution of altruism3. Prices equation and multi-level selection4. Contextual analysis and multi-level selection5. The neighbour approach6. Recapitulation and conclusion Introduction Multi-level selection and the evolution of altruism Prices equation and multi-level selection Contextual analysis and multi-level selection The neighbour approach Recapitulation and conclusion

Multilevel selection and the major transitions in evolution

A number of recent biologists have used multilevel selection theory to help explain the major transitions in evolution. I argue that in doing so, they have shifted from a ‘synchronic’ to a ‘diachronic’ formulation of the levels of selection question. The implications of this shift in perspective are explored, in relation to an ambiguity in the meaning of multilevel selection. Though the ambiguity is well‐known, it has never before been discussed in the context of the major transitions.

MULTILEVEL SELECTION AND THE PARTITIONING OF COVARIANCE: A COMPARISON OF THREE APPROACHES

Abstract Where the evolution of a trait is affected by selection at more than one hierarchical level, it is often useful to compare the magnitude of selection at each level by asking how much of the total evolutionary change is attributable to each level of selection. Three statistical partitioning techniques, each designed to answer this question, are compared, in relation to a simple multilevel selection model in which a traits evolution is affected by both individual and group selection. None of the three techniques is wholly satisfactory: one implies that group selection can operate even if individual fitness is determined by individual phenotype alone, whereas the other two imply that group selection can operate even if there is no variance in group fitness. This has significant implications both for our understanding of what the term “multilevel selection” means and for the traditional concept of group selection.

Fisher's Fundamental Theorem of Natural Selection—A Philosophical Analysis

This paper provides a philosophical analysis of the ongoing controversy surrounding R.A. Fishers famous ‘fundamental theorem’ of natural selection. The difference between the ‘traditional’ and ‘modern’ interpretations of the theorem is explained. I argue that proponents of the modern interpretation have captured Fishers intended meaning correctly and shown that the theorem is mathematically correct, pace the traditional consensus. However, whether the theorem has any real biological significance remains an unresolved issue. I argue that the answer depends on whether we accept Fishers non-standard notion of environmental change, on which the theorem rests; arguments for and against this notion are explored. I suggest that there is a close link between Fishers fundamental theorem and the modern ‘genes eye’ view of evolution. 1. Introduction2. What Does the Fundamental Theorem Say?3. Key Concepts Explained4. Alleged Significance of the FTNS5. Traditional versus Modern Interpretations of the FTNS6. The Modern Interpretation Illustrated7. Fishers Concept of ‘Environmental Change’8. Causality and the Modern Interpretation9. The Significance of the FTNS Re-considered Appendix Introduction What Does the Fundamental Theorem Say? Key Concepts Explained Alleged Significance of the FTNS Traditional versus Modern Interpretations of the FTNS The Modern Interpretation Illustrated Fishers Concept of ‘Environmental Change’ Causality and the Modern Interpretation The Significance of the FTNS Re-considered Appendix

Why Won't the Group Selection Controversy Go Away?

The group selection controversy is about whether natural selection ever operates at the level of groups, rather than at the level of individual organisms. Traditionally, group selection has been invoked to explain the existence of altruistic behaviour in nature. However, most contemporary evolutionary biologists are highly sceptical of the hypothesis of group selection, which they regard as biologically implausible and not needed to explain the evolution of altruism anyway. But in their recent book, Elliot Sober and David Sloan Wilson [1998] argue that the widespread opposition to group selection is founded on conceptual confusion. The theories that have been propounded as alternatives to group selection are actually group selection in disguise, they maintain. I examine their arguments for this claim, and John Maynard Smiths arguments against it. I argue that Sober and Wilson arrive at a correct position by faulty reasoning. In the final section, I examine the issue of how to apply the principle of natural selection at different levels of the biological hierarchy, which underlies the dispute between Sober and Wilson and Maynard Smith.

Altruism researchers must cooperate

Biologists studying the evolution of social behaviour are at loggerheads. The disputes — mainly over methods — are holding back the field, says Samir Okasha.

The Relation between Kin and Multilevel Selection: An Approach Using Causal Graphs

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   Introduction 2   The KS and MLS Approaches    2.1   The MLS decomposition    2.2   The KS decomposition 3   Equivalence and Causality 4   Two Problem Cases    4.1   The non-social trait case    4.2   Genotypic selection with meiotic drive 5   Casual Adequacy: A Graphical Approach    5.1   The basic idea    5.2   Graphs with individual and group variables    5.3   Cases where KS is causally adequate    5.4   Cases where MLS is causally adequate 6   Discussion    6.1   Relation to previous work 1   Introduction 2   The KS and MLS Approaches    2.1   The MLS decomposition    2.2   The KS decomposition    2.1   The MLS decomposition    2.2   The KS decomposition 3   Equivalence and Causality 4   Two Problem Cases    4.1   The non-social trait case    4.2   Genotypic selection with meiotic drive    4.1   The non-social trait case    4.2   Genotypic selection with meiotic drive 5   Casual Adequacy: A Graphical Approach    5.1   The basic idea    5.2   Graphs with individual and group variables    5.3   Cases where KS is causally adequate    5.4   Cases where MLS is causally adequate    5.1   The basic idea    5.2   Graphs with individual and group variables    5.3   Cases where KS is causally adequate    5.4   Cases where MLS is causally adequate 6   Discussion    6.1   Relation to previous work    6.1   Relation to previous work

Multi-Level Selection, Covariance and Contextual Analysis

Two alternative statistical approaches to modelling multi-level selection in nature, both found in the contemporary biological literature, are contrasted. The simple covariance approach partitions the total selection differential on a phenotypic character into within-group and between-group components, and identifies the change due to group selection with the latter. The contextual approach partitions the total selection differential into different components, using multivariate regression analysis. The two approaches have different implications for the question of what constitutes group selection and what does not. I argue that the contextual approach is theoretically preferable. This has important implications for a number of issues in the philosophical debate about the levels of selection. 1. Introduction2. Group selection and the covariance formulation of selection3. The contextual approach4. A modification of the simple covariance approach5. Consequences: frameshifting and additivity 5.1 Frameshifting 5.2 Additivity6. Conclusion Introduction Group selection and the covariance formulation of selection The contextual approach A modification of the simple covariance approach Consequences: frameshifting and additivity 5.1 Frameshifting 5.2 Additivity 5.1 Frameshifting 5.2 Additivity Conclusion

Emergence, hierarchy and top-down causation in evolutionary biology

The concept of emergence and the related notion of ‘downward causation’ have arisen in numerous branches of science, and have also been extensively discussed in philosophy. Here, I examine emergence and downward causation in relation to evolutionary biology. I focus on the old, but ongoing discussion in evolutionary biology over the ‘levels of selection’ question: which level(s) of the biological hierarchy natural selection acts at, e.g. the gene, individual, group or species level? The concept of emergence has arisen in the levels-of-selection literature as a putative way of distinguishing between ‘true’ selection at a higher level from cases where selection acts solely at the lower level but has effects that percolate up the biological hierarchy, generating the appearance of higher level selection. At first blush, this problem seems to share a common structure with debates about emergence in other areas, but closer examination shows that it turns on issues that are sui generis to biology.

Group adaptation, formal darwinism and contextual analysis

We consider the question: under what circumstances can the concept of adaptation be applied to groups, rather than individuals? Gardner and Grafen (2009, J. Evol. Biol.22: 659–671) develop a novel approach to this question, building on Grafens ‘formal Darwinism’ project, which defines adaptation in terms of links between evolutionary dynamics and optimization. They conclude that only clonal groups, and to a lesser extent groups in which reproductive competition is repressed, can be considered as adaptive units. We re‐examine the conditions under which the selection–optimization links hold at the group level. We focus on an important distinction between two ways of understanding the links, which have different implications regarding group adaptationism. We show how the formal Darwinism approach can be reconciled with G.C. Williams’ famous analysis of group adaptation, and we consider the relationships between group adaptation, the Price equation approach to multi‐level selection, and the alternative approach based on contextual analysis.