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    Mechanisms and functions

    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?

     

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    5 responses to “Mechanisms and functions”

    1. Trevor Avatar
      Trevor

      Other biologists (together with philosophers) have claimed that function talk in biology does not necessarily invoke selective history: http://link.springer.com/article/10.1007%2FBF00850375 (I actually thought Craver supported a “causal role” rather than a “selected effect” notion of function.)

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    2. Eric Winsberg Avatar
      Eric Winsberg

      Hi Trevor,
      The review claims that ” The authors’ notion of “proper function” of a part (and presumably, a process) is defined as “the role the part played in the evolutionary history of the organisms that have it.” ” Maybe Craver has claimed otherwise elsewhere.
      I wonder though: if one defines function in terms of causal role, doesn’t one embrace the other horn of Newman’s dilemma? What does it leave to say about ” How are living things like and unlike these and other complex products of nature? More particularly, what is the relation between the mechanisms in organisms to the unique characteristics of the living state?”

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    3. Trevor Avatar
      Trevor

      I was thinking of this paper, which I haven’t read in years: http://philpapers.org/rec/CRARFM
      I think supporters of the “causal role” notion of function just happily seize that other horn. They just give up on the notion of a ‘proper’ function; what counts as a function depends on how on defines the system.

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    4. Taylor S Murphy Avatar
      Taylor S Murphy

      Having read the book manuscript a while ago, I’m also surprised that Newman got the idea that mechanisms are paired 1-1 with “proper functions.” And developmental systems drift, spandrels and other such differences are not gonna be news to the authors. I can see why they come apart though; for any given organismal part/activity there may be various mechanisms behind it, varying between species and such as well as within the same lineage over time. I suppose it goes to show that there is no deep connection between particular mechanisms and the identity of an organism’s parts, like its systems, activities, entities, etc.
      My thought is that the unfortunate phrase “proper function” is to blame here, because this makes it seem like “proper” functions are significant and somehow the best or most important kind of functions, even though causal role in a system is the central sort of function in the book. That would explain how Newman gets the idea that “proper functions” are purportedly a “privileged set of phenomena, and mechanisms, that are essential to the living state, or to the organism in question.” I’m not a fan of the phrase either. I’m not sure where it comes from. It reminds me of Mayr’s “ultimate” explanations as the one tied to selection history.

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    5. Trevor Avatar
      Trevor

      The phrase ‘proper function’ comes from Ruth Millikan: http://books.google.com/books?id=jncHBAYe8TkC&lpg=PP1&pg=PA17#17

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