A variational synthesis of evolutionary and developmental dynamics

This paper introduces a variational formulation of natural selection, paying special atten-
tion to the nature of ‘things’ and the way that different ‘kinds’ of ‘things’ are individuated from —
and influence—each other. We use the Bayesian mechanics of particular partitions to understand
how slow phylogenetic processes constrain —and are constrained by —fast, phenotypic processes.
The main result is a formulation of adaptive fitness as a path integral of phenotypic fitness. Paths of
least action, at the phenotypic and phylogenetic scales, can then be read as inference and learning
processes, respectively. In this view, a phenotype actively infers the state of its econiche under a
generative model, whose parameters are learned via natural (Bayesian model) selection. The ensu-
ing variational synthesis features some unexpected aspects. Perhaps the most notable is that it is not
possible to describe or model a population of conspecifics per se. Rather, it is necessary to consider
populations of distinct natural kinds that influence each other. This paper is limited to a description
of the mathematical apparatus and accompanying ideas. Subsequent work will use these methods
for simulations and numerical analyses —and identify points of contact with related mathematical
formulations of evolution.

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