Samir Okasha

Marc Lange has criticized my assertion that relative to a Bayesian conception of inductive reasoning, Hume's argument for inductive scepticism cannot be run. I reply that the way in which Lange suggests one should run the Humean argument in a Bayesian framework ignores the fact that in Bayesian models of learning from experience, the domain of an agent's probability measure is exogenously determined. I also show that Lange is incorrect to equate probability distributions which 'support inductive inferences' with probability distributions which assign probability to contingent propositions/events

The levels of selection problem was central to Maynard Smith’s work throughout his career. This paper traces Maynard Smith’s views on the levels of selection, from his objections to group selection in the 1960s to his concern with the major evolutionary transitions in the 1990s. The relations between Maynard Smith’s position and those of Hamilton and G.C. Williams are explored, as is Maynard Smith’s dislike of the Price equation approach to multi-level selection. Maynard Smith’s account of the ‘core Darwinian principles’ is discussed, as is his debate with Sober and Wilson (1998) over the status of trait-group models, and his attitude to the currently fashionable concept of pluralism about the levels of selection.

Many philosophers agree that Hume was not simply objecting to inductive inferences on the grounds of their logical invalidity and that his description of our inductive behaviour was inadequate, but none the less regard his argument against induction as irrefutable. I argue that this constellation of opinions contains a serious tension. In the light of the tension, I re-examine Hume’s actual sceptical argument and show that the argument as it stands is valid but unsound. I argue that it can only be converted into a sound one if our inductive behaviour can be characterized as a process of rule-governed ampliation. Drawing on some Bayesian ideas, I argue that our inductive behaviour probably cannot be characterized in that way, so our immunity from Hume is secure. Finally, I compare my response to Hume’s argument with some other well known responses.

An evolutionary basis for Bayesian rationality is suggested, by considering how natural selection would operate on an organism’s ‘policy’ for choosing an action depending on an environmental signal. It is shown that the evolutionarily optimal policy, as judged by the criterion of maximal expected reproductive output, is the policy that, for each signal, picks an action that maximizes conditional expected output given that signal. This suggests a possible route by which Bayes-rational creatures might have evolved.

My comments will focus on the second and third chapters of Sober’s book , which explore Darwin’s ideas about altruism, group selection and kin selection , and sex-ratio evolution . Sober makes a persuasive argument for his main claim: that Darwin was a subtler thinker on these topics than he is often taken to be. While there is much that I admire in Sober’s lucid discussion, I will focus on points of disagreement. Readers should note that this is not the first time that Sober and I have disagreed on these issues .Sober begins his chapter on group selection with a brief history of the modern debate on the topic, which began in earnest in the 1960s. One of the key figures in this debate was George Williams, whose book Adaptation and Natural Selection helped convince many biologists that group selection was unlikely to be an important factor in evolution. Sober is critical of many of Williams’ arguments, though ..

The idea that natural selection can operate on cultural as well as genetic variation is central to recent theories of cultural evolution. This raises an overarching question: how much of traditional evolutionary theory, which was formulated in population-genetic terms, can survive intact once the possibility of cultural inheritance is taken into account? This question is addressed in relation to R. A. Fisher’s “fundamental theorem” of natural selection. Though Fisher’s theorem may appear to be an essentially genetic result, a version of the theorem can be derived that applies to any evolving population, with an arbitrary inheritance mechanism. However, I argue that the biological significance of this “generalized” version of the fundamental theorem is less than that of the Fisherian original

Many philosophers argue that Bayesian epistemology cannot help us with the traditional Humean problem of induction. I argue that this view is partially but not wholly correct. It is true that Bayesianism does not solve Hume’s problem, in the way that the classical and logical theories of probability aimed to do. However I argue that in one important respect, Hume’s sceptical challenge cannot simply be transposed to a probabilistic context, where beliefs come in degrees, rather than being a yes/no matter.

Advocates of the "strong programme" in the sociology of knowledge have argued that, because scientific theories are "underdetermined" by data, sociological factors must be invoked to explain why scientists believe the theories they do. I examine this argument, and the responses to it by J.R. Brown (1989) and L. Laudan (1996). I distinguish between a number of different versions of the underdetermination thesis, some trivial, some substantive. I show that Brown's and Laudan's attempts to refute the sociologists' argument fail. Nonetheless, the sociologists' argument falls to a different criticism, for the version of the underdetermination thesis that the argument requires, has not been shown to be true.

This paper compares two well-known arguments in the units of selection literature, one due to , the other due to . Both arguments concern the legitimacy of averaging fitness values across contexts and making inferences about the level of selection on that basis. The first three sections of the paper shows that the two arguments are incompatible if taken at face value, their apparent similarity notwithstanding. If we accept Sober and Lewontin's criterion for when averaging genic fitnesses across diploid genotypes is illegitmate, we cannot accept Sober and Wilson's criterion for when averaging individual fitnesses across groups is illegitimate, and vice versa. The final section suggests a possible way of reconciling the two arguments, by invoking an ambiguity in the concept of genic selection.

The ‘levels of selection’ question is one of the most fundamental in evolutionary biology, for it arises directly from the logic of Darwinism. As is well-known, the principle of natural selection is entirely abstract; it says that any entities satisfying certain conditions will evolve by natural selection, whatever those entities are. (These conditions are: variability, associated fitness differences, and heritability (cf. Lewontin 1970).) This fact, when combined with the fact that the biological world is hierarchically structured, i.e. smaller biological units are nested within larger ones, gives rise to the levels of selection question. For in principle, entities at many different hierarchical levels, above and below that of the ‘individual organism’, (e.g. gene, chromosome, cell, kin group, colony, lineage, species) can satisfy the requirements for Darwinian evolution. This possibility has long been recognised by biologists, from Darwin himself to contemporary proponents of ‘multi-level selection’; and there exist numerous biological phenomena which suggest that it has actually occurred

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.

In models of multi-level selection, the property of Darwinian fitness is attributed to entities at more than one level of the biological hierarchy, e.g. individuals and groups. However, the relation between individual and group fitness is a controversial matter. Theorists disagree about whether group fitness should always, or ever, be defined as total (or average) individual fitness. This paper tries to shed light on the issue by drawing on work in social choice theory, and pursuing an analogy between fitness and utility. Social choice theorists have long been interested in the relation between individual and social utility, and have identified conditions under which social utility equals total (or average) individual utility. These ideas are used to shed light on the biological problem.

A number of recent philosophers, including Michael Williams, Barry Stroud and Donald Davidson, have argued that scepticism about the external world stems from the foundationalist assumption that sensory experience supplies the data for our beliefs about the world. In order to assess this thesis, I offer abrief characterisation of the logical form of sceptical arguments. I suggest that sceptical arguments rely on the idea that many of our beliefs about the world are ‘underdetermined’ by the evidence on which they are based. Drawing on this characterisation of scepticism, I argue that Williams, Stroud andDavidson are right to see the foundationalist assumption as essential to the sceptic’s argument, but wrong to think that scepticism is inevitable once that assumption is in place. By pursuing an analogy with some recent debates in the philosophy of science, I try to locate the additional assumptions which the sceptic must make, in order to derive her conclusion.

It is customary to distinguish experimental from purely observational sciences. The former include physics and molecular biology, the latter astronomy and palaeontology. Experiments involve actively intervening in the course of nature, as opposed to observing events that would have happened anyway. When a molecular biologist inserts viral DNA into a bacterium in his laboratory, this is an experiment; but when an astronomer points his telescope at the heavens, this is an observation. Without the biologist’s handiwork the bacterium would never have contained foreign DNA; but the planets would have continued orbiting the sun whether or not the astronomer had directed his telescope skyward. The observational/experimental distinction would probably be difficult to make precise 1, as the notion of an ‘intervention’ is not easily defined, but it is intuitively fairly clear, and is frequently invoked by scientists and historians of science. Experimentation, or ‘putting questions to nature’, is often cited as a hallmark of the modern scientific method, something that permitted the enormous advances of the last 350 years. And it is sometimes said that the social sciences lag behind the natural because controlled experiments cannot be done so readily in the former. Moreover in certain sciences, e.g. epidemiology, students are explicitly taught that experimental data is preferable to observational data, particularly for doing causal inference. So the distinction between observational and experimental science has quite wide currency, and is often regarded as methodologically significant. Surprisingly, mainstream philosophy of science has had rather little to say about the observational/experimental distinction. 2 For example, discussions of confirmation usually invoke a notion of ‘evidence’, to be contrasted with ‘theory’ or ‘hypothesis’; the aim is to understand how the evidence bears on the hypothesis. But whether this ‘evidence’ comes from observation or experiment generally plays no role in the discussion; this is true …