Collectives Particle ByProducts

Finally, what about cross-level by-products in the downward direction Could selection at the collective level, of the MLS2 sort, produce a character-fitness covariance at the particle level Some care is needed with this idea. Recall that in MLS2, particle-level selection takes place within each collective, so there is a different particle-level character-fitness covariance for each collective. As before, we let Covk (w, z) be the covariance between particle character z and particle fitness w...

Additivity and the Wimsatt Lloyd Approach

Wimsatt (1980) and Lloyd (1988) both argue that the concept of additivity holds the key to the levels-of-selection question. Additivity is another word for linearity. If two factors combine additively to produce a given effect, this means that the effect is a linear function of each factor's contribution. Less than perfect additivity means that the difference made by one factor depends on the other factor's contribution, so the factors interact. Non-additivity is one way that emergence might be...

Selection On Correlated Characters

It helps to think abstractly about why two variables might correlate in the absence of a causal link between them. One obvious reason is if they are joint effects of a common cause. Suppose that alcohol consumption causes both obesity and kidney failure. These two conditions will correlate, even though they are causally independent obesity does not cause kidney failure, and kidney failure does not cause obesity. This familiar point is illustrated in Figure 3.1, where the thick arrows indicate...

Particle Heritability and Collective Heritability

In Chapter 1, we saw that selection only produces an evolutionary response if the character subject to selection, that is, that covaries with fitness, is heritable. Heritability means parent offspring resemblance it is measured by the regression of offspring on parent character. In principle it should be straightforward to extend the notion ofheritability 18 As Damuth and Heisler (1988) say, 'once one has decided to analyse a given situation in terms of multilevel selection processes both...

Statistical Versus Causal Decomposition

Despite its inherently statistical nature, the Price equation is often glossed in causal terms. Cov (w, z) is often described as the component 13 This allows standard population-genetic formulae for allele frequency change to be derived directly from Price's equation see Michod (1999) p. 57 for an example. 14 This point has been made repeatedly in relation to Price's equation and related formalisms, e.g. by Wade and Kalisz (1990), Heisler andDamuth (1987), Endler (1986), Lande and Arnold...

Reductionism And Pluralism Revisited

In the light of the foregoing, we can now revisit the topics of pluralism and reductionism discussed in Chapter 4. Recall that according to pluralists, the question 'at what level(s) is selection acting ' need not have a unique answer different answers 12 Though see Haldane's (1964) 'A Defence of Beanbag Genetics'. A good analysis of the beanbag genetics controversy is provided by de Winter (1997). may be equally correct. Pluralism has often surfaced in the debate over genic selection and the...

Contextual Analysis Further Remarks

Contextual analysis was introduced into the levels-of-selection discussion to deal with cross-level by-products running from lower to higher levels, 14 As Heisler and Damuth (1987) say, the Cov (W, Z) term of the Price equation is 'an expectation for the individuals of the population, not for the groups themselves' (p. 585). (Read 'particle' for individual and 'collective' for group to translate this into our terminology.) This point is easily missed, given the simplifying assumption that all...

Origins Of The Group Selection Controversy

The origin of the group selection concept lies in Darwin's remarks on the evolution of worker sterility in social insects (Darwin 1859). Sterile workers do not reproduce themselves, but devote their whole lives to assisting the reproductive efforts of the queen. Such behaviour cannot easily evolve by individual selection, as Darwin realized, for it reduces individual fitness. But he suggested that colony-level selection might provide the answer. For colonies compete with other colonies this...

Pluralism and Multiple Representations

The third source of pluralism arises from the fact that a single evolutionary process can often be modelled, or mathematically represented, in different ways. In itself, this is unsurprising. Models in science provide an idealized description of reality, focusing on some features at the expense of others. So constructing a model requires making a choice about which features to leave out different choices will lead to alternative representations of the same event or process. Importantly, the...

Info

_(2000b) 'Information, Arbitrariness and Selection Comments on Maynard Smith', Philosophy ofScience 67, 2, 202-7. _(forthcoming) 'Varieties of Population Structure and the Levels of Selection'. _and Kerr, B. (2002) 'Group Fitness and Multi-level Selection Replies to Commentaries', Biology and Philosophy 17, 4, 539-49. Goodnight, C. J., Schwartz, J. M., and Stevens, L. (1992) 'Contextual Analysis of Models of Group Selection, Soft Selection, Hard Selection, and the Evolution of Altruism',...

Emergent Relations and the Damuth Heisler Approach

In two papers on multi-level selection, Heisler and Damuth 1987 and Damuth and Heisler 1988 provide an insightful discussion of emergence, and link it to the contextual approach to MLS1. They argue that emergence is relevant to the levels of selection, but not in the way that advocates of the emergent character requirement have thought. The crucial question is not whether a given character is emergent rather than aggregate, but whether the relation between the character and fitness is emergent,...

Particle Characters and Collective Characters

Suppose that the particles vary with respect to a measurable character, denoted z. What does this imply about the characters of the collectives in which the particles reside Intuitively, we can distinguish between collective characters that derive directly from underlying particle characters, and those that do not. An example of the former is 'average z-value of the particles in a collective', or Z. Clearly, this collective character is logically determined by the...

The Averaging Fallacy

Sober and Wilson 1998 argue that the importance of group selection in evolution has been obscured by what they call the 'averaging fallacy'. Those who commit this fallacy are prone to claim that certain selection processes involve only individual selection, when in fact they involve a component of group selection. Indeed, Sober and Wilson say 'the controversy over group selection and altruism in biology can be largely resolved simply by avoiding the averaging...

Pluralism and Hierarchical Organization

A quite different motivation for pluralism stems from worries about the reality of the biological hierarchy itself. Our abstract treatment of multi-level selection assumes the existence of part whole structure. But disagreements over such structure are possible. For example, some theorists regard social bacteria colonies as genuine wholes others regard them as mere aggregates, lacking true individuality cf. Szathmary and Wolpert 2003 Shapiro and Dworkin 1997 . Analogous disagreements surround...

The Concept Of Clade Selection

I turn now to clade selection, discussed by authors including Williams 1992 , Sterelny 1996a , Vermeij 1996 , and Nunney 1999 . A clade is a monophyletic group of species, that is, a group comprising an ancestral species, all of its descendent species, and nothing else. Clades are thus located further up the genealogical hierarchy than species.7 Clade selection is often presented as a natural generalization of species selection. Thus, for example, Williams 1992 writes 'there is no reason why...

The Emergent Character Requirement

Recall that in a multi-level scenario, where particles are nested in collectives, we can distinguish between emergent and aggregate characters of the collectives cf. Chapter 2, Section 2.2.1 . Many theorists have suggested that the aggregate emergent distinction is somehow related to the levels-of-selection problem Vrba 1989 Nunney 1993 Maynard Smith 1983 . One version of this idea says that genuine collective-level selection, that is not reducible to selection at the particle level, can only...

The Two Types of Multi Level Selection

I turn now to an important ambiguity in the concept of multi-level selection, discussed by authors including Arnold and Fristrup 1982 , Sober 1984 , Mayo and Gilinsky 1987 , Damuth and Heisler l988 , Okasha 2001 and others. The ambiguity arises because there are two things that multi-level selection can mean, that is, two ways that the basic Darwinian principles can be extended to a hierarchical setting. The ambiguity has usually been discussed in relation to individual and group selection, but...

Michod On Fitness Decoupling And The Emergence Of Individuality

Consider again the model life cycle depicted in Figure 8.2. This model presumes that the transition has proceeded far enough so that the multicelled organisms can possess fitnesses in the MLS2 sense, that is, a process of reproduction at the organismic level takes place. An organism's fitness is its number of offspring propagules this number may be influenced by various factors. One important factor, Michod argues, is the frequency of cooperating C cells in the adult. The higher this frequency,...

Maynard Smith Versus Sober And Wilson On Group Heritability

The group selection question is about 'whether there are entities other then individuals with the properties of multiplication, heredity and variation, and that therefore evolve adaptations by natural selection' 1987a p. 121 . In the process envisaged by Wynne-Edwards, the groups do possess these proper-ties for they are 'sufficiently isolated for like to beget like' p. 123 . But in Wilson's trait-group model, where the groups periodically blend into the...