The problem of change in Darwinian mechanics: An Aristotelian critique through evo-devo explanation of Morphospace
Résumé
The Aristotelian notion of movement is often said to have been overcome by the two great revolutions that inaugurated modern scientific thought: Newtonian physics and Darwinian biology. Aristotle's metaphysical framework was fundamentally developed within biology, which is often ignored when interpreting his philosophy from the Physics. In particular, he conceived movement as covering both motion (kinêsis) and change (metabolê) developing the former in analogy with the latter: light bodies move up and the heavy ones down towards their natural place just like an embryo changes (i.e. actualises its essential potentiality) towards its natural mature stage. The success of Classical mechanics lays on the rupture of this essential linkage between motion and change, thus avoiding reference to essences and potentialities on the foundation of mechanics. Interestingly the Darwinian account of evolutionary change, I shall argue, was based on an analogous conceptual turn. The parallelism between the Newtonian revolution in physics and Darwinian evolutionary biology becomes explicit in the Malthusian population growth model. Paraphrasing the first of Newton's laws, its biological counterpart could be expressed as follows: every biological population remains the same and perseveres in its state of exponential growth, unless it is compelled to change that state by the forces of natural selection impressed upon it. Within this formulation, like in mechanics, an external force becomes responsible for changes in evolution; in turn, Natural history assumes the role of kinematics (restricted to the description of the geometry of evolution) and Selection theory becomes the counterpart of dynamics (in charge of explaining its causes). In doing so, Darwin (ignoring biological essences and potentialities) committed the opposite move made by Aristotle, i.e. to explain evolutionary change with the conceptual apparatus that succeed explaining physical motion. However, the Aristotelian notion of change re-emerges today within current alternatives to Darwinian externalist accounts of evolutionary change. In particular, the evo-devo analysis of morphospace implicitly recovers the old Aristotelian dialectics between essences and potentialities. Developmental change reappears intertwined with evolutionary motion in th
e form of the evolutionary actualisation of a restricted number of morphological possibilities.