On the Explanatory Roles of Natural Selection

Abstract

Can selection explain why individuals have the traits they do? This question has generated significant controversy. I will argue that the debate encompasses two separable aspects, to detrimental effect: (1) the role of selection in explaining the origin and evolution of biological traits and (2) the implications this may have for explaining why individuals have the traits they do. (1) can be settled on the basis of evolutionary theory while (2) requires additional, extra-scientific assumptions. By making a distinction between traits affected by a single factor and traits affected by multiple factors I show that selection can, under certain conditions, help explain the origin of traits. Resolving the first aspect enables us to critically assess the various incompatible and independent philosophical commitments made within the second aspect of the debate.

Students’ intuitive explanations of the causes of homologies and adaptations

“…Hence, for some scientists natural selection has a positive role and may help explain why individuals have the traits they do, whereas for others it has a negative role as it only eliminates variants and so cannot explain why an individual has particular traits. However, if one accepts that individuals belong to a lineage with a particular evolutionary history, then the latter may help explain why they have particular traits (Forber 2005).…”

Selection explanations of token traits

“…(I am assuming here that the bacterium with A is different than the bacterium with A ⁄ , not that they are the same bacterium with different versions of the allele.) Of course, we could reject origin essentialism to make this example work, but it is fairly uncontroversial that the negative view does not work if one rejects origin essentialism (Forber, 2005;Matthen, 1999;Stegmann, 2010a). The point of this paper is to present a version of the negative view that works if one does assume origin essentialism.…”

“…But Matthen argued that if one rejects ''origin essentialism''-the thesis that an organism has its parents necessarily-then the negative view falls apart (Matthen, 1999(Matthen, , 2002(Matthen, , 2003. 3 Matthen's counter-example has therefore generated a debate about origin essentialism and other trans-world identity constraints (Forber, 2005;Lewens, 2001;Matthen, 2002Matthen, , 2003Pust 2001Pust , 2004. Proponents of the negative view wish to argue that origin essentialism is plausible (or, at least, that the other proposed trans-world identity constraints are not), thereby rescuing the negative view from Matthen (Lewens, 2001;Pust, 2001Pust, , 2004.…”

Natural Selection and Multi-Level Causation

“…These ideas have led many authors to see Sober as one of the main proponents of the negative view of natural selection (Endler 1986;Neander 1988Neander , 1995aMatthen 1999Matthen , 2003Pust 2004;Forber 2005;Nanay 2005;McLaughlin [manuscript in preparation]). As Nanay put it: "Sober claims that selection is a negative force: it does not create; it only destroys" (Nanay 2005(Nanay , 1101.…”

“…From the contrary perspective, many authors have advocated a positive causal role for natural selection in shaping the traits of organisms (Ayala 1970(Ayala , 1993(Ayala , 1999Dobzhansky 1974;Jacob 1977;Dawkins 1986;Neander 1988Neander , 1995aMatthen 1999Matthen , 2003Gould 2002;Forber 2005;Nanay 2005;Godfrey-Smith 2009;McLaughlin [manuscript in preparation]). These authors defend a creative role for selection in evolution that complements its distributive role: selection is a causal factor in the generation and organization of organismal form.…”