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Function Drives Structural Development: Lessons for the Theory of Teleofunctions
Gualtiero Piccinini
In some recent posts on this blog, Hanzhe Dong and I defended the view that teleofunctions are regular contributions to goals of organisms within (reference classes within) a populatio—an account that I have developed over the last 15 years or so with help from Justin Garson and Corey Maley (see Piccinini 2020, Ch. 3, and references therein). We also argued that this improved goal-contribution account complements and extends the organismic/systemic account of functions, according to which functions are contributions by parts of an organism to the maintenance of its organization, via a network of mutually dependent processes and structures (e.g., Mossio et al. 2009).
Rival views include the view that functions (without “teleo-“) are merely causal roles (Cummins 1975) and the view that teleofunctions are selected effects (Garson 2019). Although Hanzhe and I ended on the ecumenical note that there are different notions of functions, and they can all play useful roles in our understanding of organisms and artifacts, there remains the question of which notion of function is helpful for what.
Considering how function drives structural development helps us see the unique advantages of the goal-contribution account, and why a goal-contribution account captures a core, indispensable notion of function. I mean “development” in a broad sense that includes repair and reorganization after injury.
Begin with a non-neural example: revascularization after a skin graft. Cells within the graft and cells within the host tissue are sensitive to various chemical and pressure gradients, they signal one another by using molecules such as VEGF (vascular endothelial growth factor), and they follow gradients in VEGF, blood pressure, etc. to induce first inosculation and then angiogenesis. Inosculation consists of graft capillaries connecting with host capillaries in ways that are sensitive to pressure gradients and flow cues to respect the flow structure of blood circulation in the host tissue and quickly restore some circulation in the graft tissue. Angiogenesis consists of complementing inosculation by growing new capillaries that extend the circulatory system of the host tissue into the graft tissue—again, while respecting the existing circulatory structure and function. As a result of inosculation and angiogenesis, blood circulation in the graft tissue is restored.
Now to a neural example: recovery after brain injury. Neurons within injured areas are sensitive to various chemical and electrical gradients, they send signals such as BDNF (brain-derived neurotrophic factor), and they follow such gradients in growing new axons, making new connections across the injury, and reorganizing the strength of the new synapses to restore some of the lost function.
Notice how in both cases, it is teleofunction (blood circulation, action control) that drives structural change and reorganization thanks to appropriate signals sent by cells to one another as well as other gradients (pressure, electrical) that cells are sensitive to. Ordinary organismic development is largely driven by similar mechanisms, so that, again, teleofunction contributes to structural development.
Now notice that a causal role account has no resources with which to distinguish the teleofunctions that actually drive development from the mere causal roles that various structures can exhibit. Revascularization can lead to excessive blood pressure, because the new connections are not automatically harmonized to the existing circulatory structure, but that is not a causal role among others; it’s a dysfunctional effect to be fixed through various forms of self-correction as high-pressure inflow finds low-pressure outlets. In contrast, a goal-contribution account makes sense of this: since teleofunctions contribute to the goals of organisms (by definition), organisms are built to strive for functional fulfillment (and not for the fulfillment of just any generic causal role). Notice that this is not a problematic form of teleological exaplanation because the whole process is still underwritten by ordinary efficient causes.
At first, it might seem that a selectionist account has an easier time. For, presumably, cells’ ability to send each other signals such as BDNF and VEGF, and their abilities to follow gradients, are ancient adaptations. This is certainly an important insight. But notice that those evolved capacities can function just as well in contexts for which they were presumably not adapted, such as skin grafts and brain injuries. Thus, capacities that evolved as adaptations within one context (say, to help with ordinary organismic development) can contribute to organisms’ goals in new contexts (skin grafts, recovery after brain surgery). The goal-contribution account allows us to say that such capacities are still fulfilling their teleofunction even in the new context, thus illuminating the way teleofunction drives development even in contexts in which such teleofunctions did not evolve.
Bottom line: the way teleofunction drives structural development is another place where the goal-contribution account illuminates teleofunctions in a way that other accounts do not. IMHO the notion of function as contribution to organisms’ goals is the most helpful for understanding teleofunctions within the mind sciences.
References
Cummins, Robert E. (1975). Functional analysis. Journal of Philosophy 72:741-64.
Garson, J. (2019). What Biological Functions Are and Why They Matter. Cambridge: Cambridge University Press.
Mossio, M., Saborido, C., & Moreno, A. (2009). An Organizational Account of Biological Functions. The British Journal for the Philosophy of Science.
Piccinini, G. (2020). Neurocognitive mechanisms: Explaining biological cognition. Oxford University Press.