Abstract
Natural selection comes in degrees. Some biological traits are subjected to stronger selective force than others, selection on particular traits waxes and wanes over time, and some groups can only undergo an attenuated kind of selective process. This has downstream consequences for any notions that are standardly treated as binary but depend on natural selection. For instance, the proper function of a biological structure can be defined as what caused that (type of) structure to be retained by natural selection in the past. We usually think of proper functions in binary terms: storing bile is a function of the gall bladder, but making stones is not. However, if functions arise through natural selection, and natural selection comes in degrees, then a binary approach to proper functions is in tension with the biological facts. In order to resolve this tension, we need to revise our standard accounts of proper function. In particular, we may have to seriously consider the possibility that functions themselves come in degrees, in spite of the ramifications this will have for the way we speak about functions and related concepts such as dysfunction, disease, and teleosemantic content.
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Notes
And here I am only considering selected effects accounts that concern the influence of past selection in maintaining a trait as it currently manifests, rather than earlier “etiological” accounts which concern the selective history that explains the very origin of the trait (Godfrey-Smith 1994; Griffiths 1993).
As Nicholas Shea puts it: in order to make the notion of representation less mysterious, an account of that representation needs to be in terms that are “non-semantic, non-mental and non-normative” (2013, 497).
Thanks to Stewart Saunders for bringing this example to my attention.
Much of what I say here owes a great deal to discussions with Justine Kingsbury. Additionally, a reviewer for this journal pointed out that the selective story regarding these properties may have recently reversed—minor defects in eye shape can now be medically managed or mitigated with glasses, while selection on sclera color is likely to have remained.
This example has played a notable role in past discussion of functions (e.g. Boorse 2002, 99–101). For various reasons I will use the standard peppered moth story as recounted in the relevant previous literature. However, the details of this case are more complex and ambiguous than usually described, both biologically and methodologically (Cook and Saccheri 2013). Thanks to Sam Woolley for pointing this out.
I don’t necessarily want to insist that this counterexample is completely successful, as I’m not so certain function talk is inappropriate here, and don’t want to place too much stock in unclear intuitions. The important point from our perspective is Garson’s response.
Apparently neurons do compete with one another for survival during brain remodelling in a way that could meet this requirement (Garson 2017, 538).
In a recent article working within a quite different account of functions, Justin Garson and Gualtiero Piccinini suggest that a non-negligible level of contribution to survival or fitness is required in order for some effect to qualify as a function (Garson and Piccinini 2014, 6–7). This would exclude properties that underwent positive selection extremely rarely, but within this context at least, would still admit a great many cases, depending on how one defined “negligible”.
Of course there may be all sorts of pragmatic reasons to impose thresholds on graded attributes, in the same way we might consider someone’s eighteenth birthday an important marker for the purposes of law. However, to use such a fix in this context would be tantamount to admitting that proper functions are a matter of human stipulation, and so once again lose much of what made the notion attractive in the first place.
Although see (Griffiths 1993, p. 419) and (Kingsbury 1999, p. 38–39).
Some non-functional effects may still remain. As Colin Klein pointed out to me, there would still need to be adequate variation in these traits, and in as much as they are forced side-effects of other selected traits, such variation won’t obtain. For example, if there are are no heart valve variants which are both effective and quiet, this selective story won’t obtain. Nevertheless, there will still be hugely many partial functions in the world if we adopt this graded view.
Nicholas Shea has addressed the idea that certain circumstances might cause the relevant functions to be “marginal”, although for different reasons than those discussed here. He considers these to be cases where the representational content is “genuine”, but of potentially reduced explanatory relevance (Shea 2018, 65). Many thanks to a reviewer for this journal for bringing this to my attention.
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Acknowledgements
This work was supported by the Marsden Fund of New Zealand, Fast-Start Grant number 18-MAU-063. Correspondence and comments from Justine Kingsbury were particularly important throughout the development of this article. I also acknowledge extremely useful feedback from two anonymous referees for this journal and audiences at: the Australian National University PhilSoc seminar, the Portland philosophy of science seminar series, the Australasian Association of Philosophy’18 meeting, the ISHPSSB’19 meeting, and the University of Auckland philosophy of biology reading group. Many thanks to everyone.
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Matthewson, J. Does proper function come in degrees?. Biol Philos 35, 39 (2020). https://doi.org/10.1007/s10539-020-09758-y
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DOI: https://doi.org/10.1007/s10539-020-09758-y