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Molecular Challenges to Adaptationism

We examine how molecular challenges to adaptationism, as recently put into philosophical focus by Sarkar (2015), fare against different types of adaptationist theses that have been distinguished in the philosophical debate on adaptationism. Our aim is to defend a weak form of empirical adaptationism according to which a majority of phenotypic traits at the organismal level are fixed by natural selection. Sarkar (2015) indicates a possible puzzle for this view by claiming that the same arguments that challenge adaptationism at the level of the genome can potentially apply at higher levels. We argue that many of the disputes about the importance of neutrality of molecular evolution as a challenge to the adaptationist thesis stem from unprecise use of terms such as phenotypic traits or complex phenotypes. As an important step toward a solution of this problem, we propose a strategy that tracks how changes at the molecular level can cause phenotypic effects at the organismal level, and identifies as important those phenotypic changes where a new function at the organismal level was introduced. We argue that for such cases, it is justified to conclude that selection was responsible for the fixation of a new trait. While this does not yet vindicate empirical adaptationism until further empirical research is done, it does provide us with the strategy of testing it. It shows how the puzzle can be solved by pointing to cases where new and important functions at the organismal level arise and where it can be clearly shown that selection was strong enough to counteract the effects of drift.

adaptationism, molecular evolution, neutral theory, genomics, evidence, biological function

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