Evolutionary Developmental Biology and the Limits of Philosophical Accounts of Mechanistic Explanation

Abstract

Evolutionary developmental biology (evo-devo) is considered a 'mechanistic science,' in that it causally explains morphological evolution in terms of changes in developmental mechanisms. Evo-devo is also an interdisciplinary and integrative approach, as its explanations use contributions from many fields and pertain to different levels of organismal organization. Philosophical accounts of mechanistic explanation are currently highly prominent, and have been particularly able to capture the integrative nature of multifield and multilevel explanations. However, I argue that evo-devo demonstrates the need for a broadened philosophical conception of mechanisms and mechanistic explanation.Mechanistic explanation (in terms of the qualitative interactions of the structural parts of a whole) has been developed as an alternative to the traditional idea of explanation as derivation from laws or quantitative principles. Against the picture promoted by Carl Craver, that mathematical models describe but usually do not explain, my discussion of cases from the strand of evo-devo which is concerned with developmental processes points to qualitative phenomena where quantitative mathematical models are an indispensable part of the explanation. While philosophical accounts have focused on the actual organization and operation of mechanisms, properties of developmental mechanisms that are about how a mechanism reacts to modifications are of major evolutionary significance, including robustness, phenotypic plasticity, and modularity. A philosophical conception of mechanisms is needed that takes into account quantitative changes, transient entities and the generation of novel types of entities, feedback loops and complex interaction networks, emergent properties, and, in particular, functional-dynamical aspects of mechanisms, including functional (as opposed to structural) organization and distributed, system-wide phenomena. I conclude with general remarks on philosophical accounts of explanation.

Evo-devo: a science of dispositions

“…32 Indeed, a holistic conception of organisms and their developmental sub-systems, itself once much maligned as being irrevocably wedded to the failed project of vitalism, is now a prominent feature of many evo-devo frameworks. 33 Within these frameworks, the higher-order functions of developmental systems are understood as novel, emergent features "arising" from the elemental collections which compose those systems (Wimsatt 2000;Callebaut et al 2007;Mitchell 2012;Walsh 2013;Brigandt 2015), and are accredited with playing a causal-cum-explanatory role within the process of development which is irreducibly unique, insofar as its dynamic features are attributable to these systems only qua holistic structures (Boogerd et al 2005;Huneman 2010;Nathan 2012;SalazarCiudad & Jernvall 2013).…”

The Philosophy of Biology

“…Others have taken a more ontological angle, arguing that the individuation of mechanisms ought to include their active role in delimiting a certain range of ontological dynamism among their constituents and activities: given that the characteristic function of biological systems is often (if not always) expressed via a kind of controlled fluctuation of their compositional elements and the causal connectives between them over time, a directive principle of constitutional dynamism must be incorporated in to our "mechanism" concept (Bechtel & Abrahamsen 2010;Brigandt 2015;Kaplan 2015).…”

The ontology of organisms: Mechanistic modules or patterned processes?

“…Due to the phenomenon of robustness, and thus their existential persistence throughout various alterations in their constitutive regulatory structures, these modules are commonly understood as emergent -that is, as novel, "higherorder" entities whose unique features ensure that they are incapable of being either ontologically or explanatorily reducible to any particular set of constitutive, "lower-level" entities (Wimsatt 2000;Callebaut et al 2007;Mitchell 2012;Walsh 2013;Brigandt 2015). Typically, emergent entities are understood as resisting these forms of reduction due to their possession of novel (often downwardly directed) causalcum-explanatory power which is neither had by, nor combinatorially attainable by the linear composition of their lower-level constituents (Andersen et al 2000;Ellis et al 2012).…”

“…22 How is the defender of a mechanistic ontology to respond? A popular reply to this worry is to insist that it simply misses the mark in virtue of the fact that the static conception of "mechanism" it trades on is outmoded and should be abandoned: entities and activities are no doubt central to our contemporary concept of "mechanism", but so is a particular dynamism among those elements, and the correct concept must reflect that (Bechtel & Abrahamsen 2010;Brigandt 2015;Kaplan 2015). Here the defender of a mechanistic ontology is essentially calling for a reform of her concept of "mechanism".…”

“…Though as I have already argued, even if they possess explanatory power in this respect, it is ultimately (ontologically) derived from the features of underlying operative mechanisms. For related discussions, see Kaplan & Craver (2011), Brigandt (2015, and Kaplan (2015). appropriately dynamic definition of "mechanism" ought to be understood as not only acceptable, but only natural.…”