Foundational Papers in Complexity Science pp. 71–87
DOI: 10.37911/9781947864528.04
The Shadow of a Mechanism
Author: Walter Fontana, Harvard University
Excerpt
I stumbled across Conrad H. Waddington’s 1942 paper a few years after my PhD while unwittingly retracing some of his thinking in the context of a narrow but illustrative toy-model of development, understood as a mapping from genotype to phenotype(s) (see Ancel and Fontana 2000; Fontana 2002). Digesting his paper and following its thread through his other writings made it clear that I hadn’t said much that Waddington didn’t already say fifty years prior. His prescience and subtle precision of thought at a time when far less was known than today are stunning. This is my brief take on it.
The Darwinian framework of evolution through heritable variation and natural selection is the foundation for explaining adaptation, the functional integration of living systems and their environment. Consider, for example, the evolution of different shapes of bird beaks, such as long and pointed or short and stout, adapted to tapping distinct sources of food like fruits, seeds, or insects. A short and thick beak is not a useful tool for picking seeds from a cactus. As a consequence, there is a tendency for evolution to remodel the beak in a search process based on mutation and selection as posited by the Darwinian framework. Varying the timing of the action of “calmodulin,” “bone morphogen protein 4,” and other molecular players makes mechanistically intelligible how a blind evolutionary process can find a suitable beak (Wu et al. 2004; Abzhanov et al. 2004; Mallarino et al. 2011). Waddington did not know about any of these, but not knowing exactly which levers mutation and selection can play with is not an impediment to being, in principle, satisfied with the conceptual adequacy of the Darwinian foundation. Today, given the impressive tapestry of empirical evidence grounding Darwin’s framework in mechanism, there is nothing implausible about the evolution of strong yet hollow bones in birds, even though we do not know in every detail how it happened.
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