Christie, Brusse, et al. argue that selected effects are insufficient to explain the prevalence of traits when selection is heterogeneous. One could object that it’s useful to ground functions in selected effects so long as selected effects are necessary to explain the prevalence of traits. This raises a challenging question: what justifies singling out selected effects from other factors that are necessary to explain the prevalence of traits when selection is heterogeneous? I consider three answers: selected effects are the only (...) factors that explain the prevalence of traits and (a) can plausibly ground functions; (b) enable biological generalization; and (c) enable representational explanation. I argue that none of these answers is satisfactory. Only the third answer might be able to justify singling out any selected effects at all (when selection is heterogeneous): the small share of selected effects that ground representations of causal particulars. Thus, I agree with Christie, Brusse, et al. that heterogeneous selection is a serious problem for selected effects theories of function. (shrink)

It’s an honour to have so many major contributors to the literature respond to our article and we thank them for their thoughtful responses. There are clear shared themes across these commentaries,...

Joshua Christie, Carl Brusse, Pierrick Bourrat, Peter Takacs, and Paul Griffiths argue that selected-effects (SE) functions generally fail to causally explain traits because they omit some explanatorily essential information. Heterogeneous environments, bet-hedging strategies, and frequency-dependence all produce selection dynamics that are explanatorily important but that are left out when we focus exclusively on the conditions under which a given trait was adaptive. Thus, they argue, the SE theory gives inadequate explanations since it only picks out a limited set of explanatorily (...) relevant factors. Some other authors in this volume have responded by trying to clarify the explanatory goals of SE functions in order to show that their omission of these phenomena is unproblematic. I take a different approach, arguing that in some important cases—including, perhaps, the case of signalling—environmental heterogeneity and coevolution can be explanatorily relevant because they are some of the functional effects of traits. I agree with the authors that these dynamics are important for explaining adaptations; however, I suggest that they need not be left out by SE explanations, because they can be among the effects for which traits are selected. Niche construction theory offers a useful framework for understanding these dynamics in this way. (shrink)

In the target article, Christie, Brusse, et al. argue that selected effect functions do not, in general, explain why a trait exists in a population and, therefore, theories of representational content should not rely on selected effect functions. This response focuses on the claim about functions-for-representation. The role of evolutionary functions in a theory of content is to pick out outcomes that have been systematically stabilized by natural selection. Correctness conditions are conditions involved in explaining how that happened. Selected effect (...) functions can play that role in the complex equilibria that Christie, Brusse, et al. identify. Non-equilibrium cases are also discussed. (shrink)

This is a response to Christie, Brusse, et al., ‘Are biological traits explained by their “selected effect” functions?’ The interest of their paper is that it draws our attention to those cases in which changes in a population that are brought about by natural selection in turn bring about changes in the environment that alter the selectionist pressures that were responsible for the original changes. Much of the paper, however, is an argument that the notion of a ‘proper function’ introduced (...) in my Language, Thought, and Other Biological Categories (LTOBC), exhibits deep misunderstandings about the actual workings of natural selection. Very little that they say about ‘proper functions’ and related notions from LTOBC is correct, however. I will not list the errors but I will try to make my uses of ‘proper function’ and certain related terms clearer. (shrink)

Christie, Brusse, et al. claim that the ‘selected effect’ (SE) theory of function is premised on a simplistic view of evolution. In complex evolutionary scenarios, in particular those involving frequency-dependent selection (FDS), the SE theory fails, they argue, since citing a trait’s SE function does not serve to explain why the trait exists. I argue that where FDS leads to a stable equilibrium, at which all individuals’ trait values constitute a ‘best response’ to the rest of the population, the SE (...) theory can be straightforwardly applied. However, matters are different if the evolutionary dynamics do not take the population to a stable equilibrium. (shrink)

Several other commentators capably articulate and defend an important objection to Christie, Brusse, et al.: the claim that the existence of a trait is entirely, rather than partially explained by the effects for which it was selected is stronger than the selected effects theorist needs or seeks to defend. Nonetheless, Christie, Brusse, et al.’s cases do draw our attention to a point about the explanatory relation between selected effects functions and their bearers that has not been emphasized by selected effects (...) theorists, although some have quietly accommodated it. This is the idea that, for a trait T to be for performing F, T’s ability to perform F must figure in an explanation of T’s existence in a particular way. It is not T’s absolute propensity to produce F as an effect but its comparative propensity, as compared with alternatives to T, that must figure in the explanation. The pattern of explanation sought by selected effects theorists to underwrite function attributions therefore requires a correct choice of comparison class. When we spell this idea out, we arrive at a hypothesis about what is bothering Christie, Brusse, et al. about the cases they find problematic. Consider their Gouldian finches. Focusing on the role of comparative propensities, the difficulty becomes clear: the claim that the red-heads’ hormonal levels have persisted in the finch population because they have had the effect of dislodging competitors more reliably than the black-heads’ hormonal levels is incorrect. The red-head phenotype doesn’t stick around by outdoing the black-heads at dislodging, since the black-heads can’t be outdone at something they are not in the business of doing in the first place. However, this point is not in the end a serious problem for selected effects theories because the problem comes from a wrong choice of comparison class: namely, black-heads, rather than inferior red-heads. If the hormonal trait of today’s red-heads reached or persists at its present frequency because of some historical selection against other, perhaps quite similar, hawkish variants, this trait will be for dislodging competitors, since it is around because it outdid those alternatives at dislodging. (shrink)

In the target article for this issue, Christie, Brusse, et al. [2022a] argue that Selected Effects Functions (SEF), at least as currently articulated, often do not explain biological traits. In res...

Christie, Brusse, et al. argue that the selected effects theory of function (SE) doesn’t do what it’s supposed to do: namely, show how functions can be explanatory. They survey some well-known evolutionary dynamics such as arms races, frequency-dependent fitness, and environmental heterogeneity, some of which have been discussed in the functions literature for decades. They argue that SE only seems to work because SE theorists ignore these dynamics. Their argument fails because they misrepresent what functions are supposed to explain and (...) how they’re supposed to do so. One reason for this failure is that they overlook the role of functions in the broader conversation about teleology in biology, one that has been unfolding for over 2000 years. (shrink)