Tuesday, February 10, 2009

Design-space, selection pressure, neither––or both plus something more?

"The notion of order is inseparable from that causality, which is itself an order of dependence. … The ability of a living being to move itself, even though it be only to assimilate and grow, involves therefore the organization of heterogeneous parts of which it is composed. This is why one says of living bodies that they are organisms or that living matter is organic [organiseé]. The finalism of Aristotle is an attempt to give a reason for the very existence of this organization. … To explain heterogeneous parts by the same principles which explain homogeneous parts is to leave deliberately unexplained the heterogeneity of the heterogeneous. … "

–– Étienne Gilson, From Aristotle to Darwin and Back Again (University of Notre Dame Press, 1984), pp. 3, 97.

Try this: extend your arm partly out, with the palm of your hand hanging facedown, like you stopped midway reaching for something, and hold that pose. Now try extending (i.e., lifting up) each finger one by one without moving any of the others: thumb, pointer, "bird", etc. Or try this: make a loos Black-Power fist, and try extending each finger one by one. What did you notice? Only the ring finger was hard to manipulate, right? Your ring finger kept "pulling" up a nearby finger, and it gave you an awkward tingle in the tendons of your wrist, right? (If I'm wrong, stop reading and go to your room!)

I mention this not as some kind of crude refutation of Berkeley's idealism, nor as a demonstration of mind-body interaction and the freedom of the will, but as an entry point into considering the standard Darwinian method of explaining current human anatomy and physiology. I will focus on what I see as twin parameters in the Darwinian method: selective pressure (based, of course, on reproductive advantage) and design-space constraints. I hope this reflection will raise interesting questions about the enduring role of teleology in the Darwinian method as it aims to be a coherent explanation of the natural order.

Selective pressure just has to do with the fact that some traits inherited by members of a relevantly connected population give some members bearing it a reproductive "edge" over others. For example, the fluke inheritance (by some panda in the jungle) of an ability to see green things more vividly than brown things, helps it find fresh leaves more easily, which, in turn, helps it live a longer and healthier life, during which time it can probably produce more offspring than its fellow pandas. As a result, its fluke acuity for green will be passed on in greater numbers, which will both give its offspring a similar advantage and undermines the viability of less acutely appeared-to-greenly pandas. Given enough time, acuity for green will become so common that a new selective Achilles' heel (or, a genetic ace in the sleeve) will take center stage. Alternatively, of course, the pandas' environment might have favored visual acuity for brown, such as if it helped pandas avoid stepping on a highly lethal species of viper in their habitat that looks to less acutely appeared-to-brownly pandas as just a stick on the ground. Obviously, the fluke inheritance of being vividly appeared-to-brownly-and-greenly will doubly enhance its bearer. Selection pressure will quickly promote such pandas at the longterm expense of their more myopic peers.

Design-space constraints have to do with the more global limits of "what evolution can do" in general, as opposed to what a local set of selection pressures favors or disfavors in one strand of evolutionary history. A common example is the eye as a trans-specific feature. Given the selective advantage of being able to see, species will thrive if they can develop some kind of visual apparatus. There is no inherent model, on the Darwinian model, for what these visual tools should look like or where they should be on a particular body in a particular species in a particular habitat. However, given the more global design limitations animals encounter on Earth (e.g., gravity, atmospheric contents, availability of potable water, seasons, ATP cycle, etc.), there are only so many viable ways for evolution to build an on-board optical device. Hence, humans, octopi, rabbits, and bats (whatever it might be like to be one of those), and basically all mobile species, not only all seem to have an "eye module," but also seem to share a core design concept, which is limited only by what is feasible in the general design-space of nature.

One of my favorite design-space limitations has to do with how large exoskeletons can be on Earth: spiders and crabs literally cannot develop past a certain size, or their own articulated exoskeletons will collapse on themselves. This is a truly global limitation (though not a lunar one)! On a smaller scale, design-space limitations might surface in the anatomy of one species, given the existence of other features already possessed by that species. For example, while it might be selectively advantageous to have a third eye in the back of our heads, and while this may pop up from time to time in our genetic history, by and large this feature will be a disadvantage for its transitional bearer, since it will not only, say, expose him to greater risk of infection (and thus brain fever, akin to fatalities associated with "the dangerous triangle" (possible yuck warning!)), or, say, compromise the strength of his already holey skull and lead to debilitating brain damage, and, in turn, not a lot of reproductive edge. The "reigning" design features of the human skull impose certain limitations on otherwise "clever" adjustments.

Now, here is what this has to do with the hand exercise I began with: it leads me to wonder how a Darwinian theorist would explain the awkwardness of our ring finger. Is it hard to extend this finger simply because of the design-space limitations imposed by adjacent fingers? Or has its awkwardness evolved in response to some kind of subtle selective advantage? Or, more importantly, does it even make sense to assign either kind of explanation to such a trivial feature of human anatomy? I assume the awkwardness of extending our ring finger is a nearly global human phenomenon. Hence, it seems to be just as wrapped up in the saga of natural selection as any other feature. Any capable Darwinist could, of course, devise a story as to "why" this strange handicap has occurred among humans. But it would seem very ad hoc, the kind of "just so" story the late Stephen Jay Gould accused too many evolutionists of confabulating. What possible selective advantage or disadvantage would this very common attribute of the human hand have sub specie evolutionis?

I raise this issue not to deny there is any such advantage, but simply to suggest that design-space limitations should get the lion's share of explanatory credit in the purely materialistic terms most Darwinists promote as a total worldview. Indeed, it seems difficult, in purely materialistic terms, to decide which features of our human nature any more or less intelligibly connected with selection than others. For, in purely materialistic terms, all our features have been developed––and conjoined––by sheer chance. There is nothing more "intrinsic" about our genitalia as formally advantageous means of reproduction than there is about our ring fingers, since either group of organs could have or could have had, a greater or lesser reproductive advantage under different selective pressures.

In any case, it seems far more rational to say our ring finger is as pitiful as it is because it's only got so much remaining design-space in which to adapt. Meanwhile, however, it is easy to spin off "reasons" why the thumb functions how it does (i.e., an opposable thumb enhances grip enhances eating enhances killing enhances breeding, etc.), or why the index and ring finger are so dexterous (i.e., similar reasons as opposable thumb, etc.). But, crucially, it is part of the neo-Darwinist method to forswear talk of "purpose" and "teleology" altogether in biological explanations. Therefore, since there is, by definition, no place for purpose in design-space limitations, it should be the primary mode of explanation for Darwinists. Since design-space limitations are the purest mode of nature blindly and bluntly using whatever comes into its grasp, the more ornate (and quickly apologetic) attempts to explain function and structure in terms of their adaptive goals, seem totally out of place in pure Darwinist terms. And yet, as Étienne Gilson explored in From Aristotle to Darwin and Back Again, those terms pervade the history and vocabulary of biological and evolutionary thought.

What all this suggests to me is that the purest form of (non-teleological) Darwinist explanation reduces an explanation of natural history to a truncated form of a mere complete description of nature as we happen to find it. The thumb functions like it does, not so we can control and kill things better, but because it is attached to an arm that functions as it does, not so we can reach or move things, but because it is attached to a spine-cum-shoulder apparatus that functions as it does, not so we can reach higher and climb, but because it is attached to a hip-cum-leg system, etc., etc. In each case, these design-space explanations negate all mention of final causation (though, with their reminder of an organ's subsidiary role in an organism, they do smack of formal causation––but forget that for now), in order to address only the mechanical, efficient, purely material conditions of cause and effect––but in so doing they cease to be explanations of development as natural selection directed them towards greater fitness. They fail to be explanations of development in the same way a bare family tree waved in front of your face fails to be a cogent explanation of a family's history. I may see that Uncle Manfried was, in 1906, in Innsbruck, and then, in 1915, in Scranton, but I still lack any internal access to how this can be explained. I see, in other words, that Uncle Manfried's "Innsbruck part" is attached to his "Scranton part," but, without an insight as to why–-viz., to what end––this shift occurred, I lack a real explanation. This self-effacing but crucial "why" (dia ti), this "in view of which" (to ou eneka), is what Aristotle means by "the end" (telos).

Likewise, while I may see the various "family tree" attachments between this organ and that, or between this older fossil and that later one, we lack the means to explain their phylogenetic development as a naturally ordered phenomenon unless we add to these attachments "snapshots" a deeper ontological framework of teleology and formal integrity. To cite Gilson: "The notion of order is inseparable from that causality, which is itself an order of dependence [p. 3]." Unless the one fossil is somehow directed towards and formally conducive of the later fossil, they are, literally, not to be grouped under one explanation; at best, they are to be grouped in one bag of metaphysically discrete artifacts that happen to strike us "somehow related." I can see their development in terms of efficient and material causation only if, ex hypothesi, I see with my own eyes a three-eyed baby born of two-eyed parents, and then witness him survive and spawn a whole race of superior triclopic humans. Only if I admit there is a finality about his genetic endowment (viz., ordered to the flourishing of the species via his mutation), and a formal integrity between his parents, him, and his offspring, will I be able to explain these phenomena under one heading. Recall Gilson's stricture in the above quotation: "To explain heterogeneous parts by the same principles which explain homogeneous parts is to leave deliberately unexplained the heterogeneity of the heterogeneous [p. 97]." That is, to explain a materially heterogeneous but formally ordered natural phenomenon only in terms of the efficient, mechanistic causality of the various homogeneous structures within it (like atoms and chemicals), is not to explain the former at all.

What I suggest, then, is basically what Edward Feser argues for by the end of The Last Superstition: namely, that Darwinism either grow content with mere design-space descriptions, or restore proper respect to the role of final and formal causation along with efficient and material causation. Because the genetic code is directed towards the production of a viable human, and because it is the formal constitution of the nutrients (material cause) built into an infant in a woman's impregnated womb (efficient cause), I can coherently account not only for its place in the larger natural cycle of birth, competition, and death, but also can see how it might lead to later adaptive advantages or disadvantages in the larger "body" of the species. Thus, to cite Gilson once more, "true finalism" is concerned with "forms immanent in nature and working from within to incarnate themselves there by modeling matter according to their law [p. 99]." As Dennis Des Chene puts it (The Cambridge Companion to Early Modern Philosophy, p. 86, as cited in TLS, p. 264, n. 49), "every power, exercised or not, has an object toward which it is directed––its intentio [or, entelechy]." Likewise, asks Celestine Bittle in The Domain of Being: Ontology (p. 364, as cited in loc. cit.), "what is a natural law, if not the expression of the inner tendencies of the nature of [physical things]?"

These final and formal dispositions of the human genome, among countless other natural entities, have, to draw on the distinction emphasized by Ric Machuga in his In Defense of the Soul, a per se causal cogency that as a specific natural cycle produces viable human, but which still allows for per accidens "flukes" and embryonic difficulties. To cite Machuga's own illustration, a geologist may be able to explain to his daughter the natural, per se mechanism by which a certain rock she finds on the path was formed, but he has no per se explanation, but only a per accidens shrug, as it were, for there being three distinct pink hearts on its surface. The kind of rock she finds is something nature produces per se, as a natural tendency, cycle, or disposition; the hearts she finds on it are something nature has indeed produced, but only per accidens. Hence, while it not only makes sense, in teleological and formal terms, to try explaining how natural selection per se "made" my "good" fingers (and humans' hands in general) to be the way they are, it also does not beg the question to admit there is no per se way to seek an explanation––as a theoretically coherent and formally natural process––how my awkward ring finger came to be the way it is by the per accidens effects of natural selection.

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