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 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)

Hierarchical expansions of the theory of natural selection exist in two distinct bodies of thought in evolutionary biology, the group selection and the species selection traditions. Both traditions share the point of view that the principles of natural selection apply at levels of biological organization above the level of the individual organism. This leads them both to considermultilevel selection situations, where selection is occurring simultaneously at more than one level. Impeding unification of the theoretical approaches of the multilevel selection traditions (...) are the different goals of investigators in the different subdisciplines and the different types of data potentially available for analysis. We identify two alternative approaches to multilevel situations, which we termmultilevel selection [1] andmultilevel selection [2]. Of interest in the former case are the effects of group membership onindividual fitnesses, and in the latter the tendencies for the groups themselves to go extinct or to found new groups (i.e., group fitnesses). We argue that: neither represents the entire multilevel selection process; both are aspects of any multilevel selection situation; and both are legitimate approaches, suitable for answering different questions. Using this formalism, we show that: multilevel selection [2] does not require emergent group properties in order to provide an explanatory mechanism of evolutionary change; multilevel selection [1] is usually more appropriate for neontological group selection studies; and species selection is most fruitfully considered from the point of view of multilevel selection [2]. Finally we argue that the effect hypothesis of macroevolution, requiring, in selection among species, both the absence of group effects on organismic fitness (multilevel selection [1]), and the direct determination of species fitnesses by those of organisms, is untestable with paleontological data. Furthermore, the conditions for the effect hypothesis to hold are extremely restrictive and unlikely to apply to the vast majority of situations encountered in nature. (shrink)

Hannah Arendt (1906-1975) is likely to be the first woman to join the canon of the great philosophers. Arendt's work has attracted a huge volume of scholarship. This collection reprints papers from the USA, Germany, France and the UK, where further scholarly work is emerging at an increasing pace. Given that there was vigorous debate of her work in her lifetime, that there have since been several waves of evaluation and re-evaluation, and because a new generation of scholars is now (...) coming to her work, a systematic collection of the critical assessments of her thought is extremely timely. (shrink)

I argue that images of the notion of group, in correspondence with their social and political values, shape the debate over the evolution of altruism by group selection. Important aspects of this debate are empirical, and criteria can decide among a variety of selection processes. However, leading researchers undermine or reinterpret such tests, explaining the evolution of altruism on the basis of a single extreme metaphor of ‘group’ and a single inclusive selection process. I shall argue that the extreme images (...) for the notion of group are associated with ideologies that these researchers support or fear. Hence, the history of social and political uses of ‘group’ and ‘group selection’ can explain, at least in part, some of the empirical deficiencies of the debate, and why it has continued without resolution or dissolution. (shrink)

Altruism is a central concept in evolutionary biology. Evolutionary biologists still disagree about its meaning (E.O. Wilson 2005; Fletcher et al. 2006; D.S. Wilson 2008; Foster et al. 2006a, b; West et al. 2007a, 2008). Semantic disagreement appears to be quite robust and not easily overcome by attempts at clarification, suggesting that substantive conceptual issues lurk in the background. Briefly, group selection theorists define altruism as any trait that makes altruists losers to selfish traits within groups, and makes groups of (...) altruists fitter than groups of non-altruists. Inclusive fitness theorists reject a definition based on within- and between-group fitness. Traits are altruistic only if they cause a direct and absolute fitness loss to the donor. The latter definition is more restrictive and rejects as cases of altruism behaviors that are accepted by the former. Fletcher and Doebeli (2009) recently proposed a simple, direct and individually based fitness approach, which they claim returns to first principles: carriers of the genotype of interest “must, on average, end up with more net direct fitness benefits than average population members.” This seductively simple proposal uses the concept of assortment to explain how diverse kinds of altruists end up on average with more net fitness than their non-altruistic rivals. In this paper I shall argue that their approach implies a new concept of altruism that contrasts with and improves on the concept of the inclusive fitness approach. (shrink)

I argue that images of the notion of group, in correspondence with their social and political values, shape the debate over the evolution of altruism by group selection. Important aspects of this debate are empirical, and criteria can decide among a variety of selection processes. However, leading researchers undermine or reinterpret such tests, explaining the evolution of altruism on the basis of a single extreme metaphor of ‘group’ and a single inclusive selection process. I shall argue that the extreme images (...) for the notion of group are associated with ideologies that these researchers support or fear. Hence, the history of social and political uses of ‘group’ and ‘group selection’ can explain, at least in part, some of the empirical deficiencies of the debate, and why it has continued without resolution or dissolution. (shrink)

Groups, individuals, and evolutionary restraints : the making of the contemporary debate over group selection Content Type Journal Article Pages 1-14 DOI 10.1007/s10539-011-9255-5 Authors Andrew Hamilton, Center for Biology and Society, School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501 USA Christopher C. Dimond, Center for Biology and Society, School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501 USA Journal Biology and Philosophy Online ISSN 1572-8404 Print ISSN 0169-3867.

Sexual reproduction is almost ubiquitous among multicellular organisms even though it entails severe fitness costs. To resolve this apparent paradox, an extensive body of research has been devoted to identifying the selective advantages of recombination that counteract these costs. Yet, how easy is it to make the transition to asexual reproduction once sexual reproduction has been established for a long time? The present review approaches this question by considering factors that impede the evolution of parthenogenesis in animals. Most importantly, eggs (...) need a diploid chromosome set in most species in order to develop normally. Next, eggs may need to be activated by sperm, and sperm may also contribute centrioles and other paternal factors to the zygote. Depending on how diploidy is achieved mechanistically, further problems may arise in offspring that stem from ‘inbreeding depression’ or inappropriate sex determination systems. Finally, genomic imprinting is another well-known barrier to the evolution of asexuality in mammals. Studies on species with occasional, deficient parthenogenesis indicate that the relative importance of these constraints may vary widely. The intimate evolutionary relations between haplodiploidy and parthenogenesis as well as implications for the clade selection hypothesis of the maintenance of sexual reproduction are also discussed. (shrink)