What can natural selection explain? Ulrich E. Stegmann Department of Philosophy, University of Aberdeen, Old Brewery, High Street, Aberdeen, AB24 3UB, United Kingdom article info Article history: Received 27 May 2009 Received in revised form 4 September 2009 Keywords: Explananda of natural selection Explanation of traits Adaptation Sober–Neander controversy The Negative View abstract One approach to assess the explanatory power of natural selection is to ask what type of facts it can explain. The standard list of explananda includes facts like trait frequencies or the survival of particular organisms. Here, I argue that this list is incomplete: natural selection can also explain a specific kind of individual-level fact that involves traits. The ability of selection to explain this sort of fact (‘trait facts’) vindicates the explanatory commitments of empirical studies on microevolution. Trait facts must be dis- tinguished from a closely related kind of fact, that is, the fact that a particular individual x has one trait rather than another. Whether or not selection can explain the latter type of fact is highly controversial. According to the so-called ‘Negative View’ it cannot be explained by selection. I defend the Negative View against Nanay’s (2005) objection. Ó 2010 Elsevier Ltd. All rights reserved. When citing this paper, please use the full journal title Studies in History and Philosophy of Biological and Biomedical Sciences 1. Introduction What kinds of facts can natural selection explain? Here is a standard list of things that at least some authors believe selection can explain: 1. The dynamics of trait frequencies in populations across time, that is, their change or stagnation (Sober, 1984); 2. The composition of a population at a particular point in time (Sober, 1995, p. 384), for example the fact that 90% of the pop- ulation are G-individuals and 10% are B-individuals (individuals with trait G or B, respectively); 3. The origin of traits in a population, in addition to their spread and maintenance as acknowledge in (1) (Forber, 2005); 4. An individual’s survival, its reproductive success (Sober, 1984, p. 152) and its existence (Sober, 1995, p. 388); 5. The fact that a particular individual has trait G rather than trait B. It is uncontroversial that selection can explain facts (1) and (2). It is also generally accepted that selection can explain (4), at least as long as selection is regarded as a causal process. 1 However, a long-standing controversy surrounds (5). Many authors deny that selection explains the traits of individuals (Sober, 1984, 1995; Walsh, 1998; Lewens, 2001; Pust, 2001, 2004), a position known as the ‘Negative View’. 2 Others insist that selection can explain this fact in special circumstances (e.g. Neander, 1995; Matthen, 1999; Forber, 2005; Nanay, 2005). More recently, Forber (2005) has added (3) to the list, arguing convincingly that under some circumstances selection explains the origin of traits. It is easy to loose sight of the significance of this debate, so much so that some may wonder whether it has any. So let me say why I think it is important, but also where its relevance may have been overstated. First, the list of explananda is not a haphaz- ard list of empirical facts for which we have good evidence that selection explains them. Debating such a list might well be tedious and pointless. Rather, the list, and the debate surrounding it, con- cerns the kinds of facts selection can explain. Identifying the kinds of facts selection can explain is imperative if the goal is to under- stand the explanatory power of natural selection. And surely, understanding the explanatory power of such a fundamental no- tion is a worthy goal for both philosophers of science and biolo- gists. The debate is essential for this project. 1369-8486/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.shpsc.2009.12.002 E-mail address: u.stegmann@abdn.ac.uk 1 The causal understanding of selection has recently come under attack (Matthen & Ariew, 2002; Walsh, 2007). 2 This is in line with Pust’s (2001,2004) use of the ‘Negative View’, but not with that of Neander (1995), who uses this expression for the view that selection cannot explain how genetic plans for traits originated. Studies in History and Philosophy of Biological and Biomedical Sciences 41 (2010) 61–66 Contents lists available at ScienceDirect Studies in History and Philosophy of Biological and Biomedical Sciences journal homepage: www.elsevier.com/locate/shpsc