Jonathan Birch

Inclusive fitness theory was not originally designed to explain the major transitions in evolution, but there is a growing consensus that it has the resources to do so. My aim in this paper is to highlight, in a constructive spirit, the puzzles and challenges that remain. I first consider the distinctive aspects of the cooperative interactions we see within the most complex social groups in nature: multicellular organisms and eusocial insect colonies. I then focus on one aspect in particular: the extreme redundancy these societies exhibit. I argue that extreme redundancy poses a distinctive explanatory puzzle for inclusive fitness theory, and I offer a potential solution which casts coercion as the key enabler. I suggest that the general moral to draw from the case is one of guarded optimism: while inclusive fitness is a powerful tool for understanding evolutionary transitions, it must be integrated within a broader framework that recognizes the distinctive problems such transitions present and the distinctive mechanisms by which these problems may be overcome

Hamilton introduced two conceptions of social fitness, which he called neighbour-modulated fitness and inclusive fitness. Although he regarded them as formally equivalent, a re-analysis of his own argument for their equivalence brings out two important assumptions on which it rests: weak additivity and actor's control. When weak additivity breaks down, neither fitness concept is appropriate in its original form. When actor's control breaks down, neighbour-modulated fitness may be appropriate, but inclusive fitness is not. Yet I argue that, despite its more limited domain of application, inclusive fitness provides a distinctively valuable perspective on social evolution.

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.

Evolution and Rationality marks the end of a three-year project, ‘Evolution, Cooperation, and Rationality’, directed at the University of Bristol by the book’s editors, Samir Okasha and Ken Binmore. The collection draws together the editors’ pick of the papers delivered at the conferences the project hosted, and covers a wide range of topics at the intersection of evolutionary theory and the social sciences. It is a splendid anthology: timely, interdisciplinary, thematically cohesive, and full of substantive and interesting disagreements between the contributors

Cooperation is rife in the microbial world, yet our best current theories of the evolution of cooperation were developed with multicellular animals in mind. Hamilton’s theory of inclusive fitness is an important case in point: applying the theory in a microbial setting is far from straightforward, as social evolution in microbes has a number of distinctive features that the theory was never intended to capture. In this article, I focus on the conceptual challenges posed by the project of extending Hamilton’s theory to accommodate the effects of gene mobility. I begin by outlining the basics of the theory of inclusive fitness, emphasizing the role that the concept of relatedness is intended to play. I then provide a brief history of this concept, showing how, over the past fifty years, it has departed from the intuitive notion of genealogical kinship to encompass a range of generalized measures of genetic similarity. I proceed to argue that gene mobility forces a further revision of the concept. The reason in short is that, when the genes implicated in producing social behaviour are mobile, we cannot talk of an organism’s genotype simpliciter; we can talk only of an organism’s genotype at a particular stage in its life cycle. We must therefore ask: with respect to which stage(s) in the life cycle should relatedness be evaluated? For instance: is it genetic similarity at the time of social interaction that matters to the evolution of social behaviour, or is it genetic similarity at the time of reproduction? I argue that, strictly speaking, it is neither of these: what really matters to the evolution of social behaviour is diachronic genetic similarity between the producers of fitness benefits at the time they produce them and the recipients of those benefits at the end of their life-cycle. I close by discussing the implications of this result. The main payoff is that it makes room for a possible new mechanism for the evolution of altruism in microbes that does not require correlated interaction among bearers of the genes for altruism. The importance of this mechanism in nature remains an open empirical question

The sense of fairness is a central aspect of human moral psychology. Intuitions about fairness lead to many widespread moral beliefs, such as the belief that the punishment should fit the crime or the belief that one deserves a fair share of what one has earned. In The Origins of Fairness, Nicolas Baumard sets out to shed light on the evolutionary origin of these intuitions. He argues that the human sense of fairness is innate and universal, and he offers an account of its evolution that highlights the role of bargaining in early human “cooperation markets.”

Nick Bostrom’s ‘Simulation Argument’ purports to show that, unless we are confident that advanced ‘posthuman’ civilizations are either extremely rare or extremely rarely interested in running simulations of their own ancestors, we should assign significant credence to the hypothesis that we are simulated. I argue that Bostrom does not succeed in grounding this constraint on credence. I first show that the Simulation Argument requires a curious form of selective scepticism, for it presupposes that we possess good evidence for claims about the physical limits of computation and yet lack good evidence for claims about our own physical constitution. I then show that two ways of modifying the argument so as to remove the need for this presupposition fail to preserve the original conclusion. Finally, I argue that, while there are unusual circumstances in which Bostrom’s selective scepticism might be reasonable, we do not currently find ourselves in such circumstances. There is no good reason to uphold the selective scepticism the Simulation Argument presupposes. There is thus no good reason to believe its conclusion.

An influential argument due to Elliott Sober, subsequently strengthened by Denis Walsh and Joel Pust, moves from plausible premises to the bold conclusion that natural selection cannot explain the traits of individual organisms. If the argument were sound, the explanatory scope of selection would depend, surprisingly, on metaphysical considerations concerning origin essentialism. I show that the Sober-Walsh-Pust argument rests on a flawed counterfactual criterion for explanatory relevance. I further show that a more defensible criterion for explanatory relevance recently proposed by Michael Strevens lends support to the view that natural selection can be relevant to the explanation of individual traits.