There appeared this morning a very interesting review of Craver and Darden’s recent book In Search of Mechanisms: Discoveries across the Life Sciences by the biologist Stuart Newman. Among the points he makes is the claim that it will no longer do for philosophers to define the function of some mechanism (or anything else) as "the role the part played in the evolutionary history of the organisms that have it” (C&D’s phrase). This is so, he argues, because the “phenomenon of ‘developmental system drift’ plays havoc with conventional ideas about mechanism.”
He gives the following examples:
In more than 20 species of nematode worms of the genus Caenorhabditis, for example, despite an invariant anatomy and the cell lineages that generate it, orthologous genes have evolved to take on qualitatively different roles and expression patterns in early embryonic pattering, sex determination, and organs of the reproductive and excretory systems, among others (Verster AJ, Ramani AK, McKay SJ, Fraser AG, PLOS Genetics 10 (2014): e1004077). In the well-known case of insect segmentation, to take another example, different species utilize distinct mechanisms, which generate segments simultaneously or sequentially, or a mixture of both, using some of the same and some different genes, with little overt difference in the outcomes (Salazar-Ciudad I, Solé, R, Newman SA, Evolution & Development 3 (2001): 95-103). It is not that detailed mechanisms cannot be identified for these developmental processes, but that their details seem less important than the higher-level morphological "attractors" that exert a kind of downward causation (a concept not mentioned in the book) on their permissible variation, which is rather prolific.
In the end, Newman wonders “whether mechanisms are among the distinctive or even most significant features of life-forms.” Given the enormous attention that the literature on mechanisms has attracted in recent years from philosophers, I’m curious what some of the philosophers of biology among our readers (and blog members!) think about this review. Can we still unproblematically talk about functions in biology?
Recent Comments