23 lines
7.9 KiB
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23 lines
7.9 KiB
Plaintext
Three kinds of teleology
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<p>Some comments on my last post sidetracked into a discussion of evolution, teleology and design and under what circumstances the language of “purpose” or “intention” can reasonably applied to a natural system. I’ve had a new insight while thinking about that discussion, so I’m going to write about it a bit more. And yes, I am aware that this discussion may appear to overlap with Daniel Dennett’s notion of the <a href="http://en.wikipedia.org/wiki/Intentional_stance">intentional stance</a>, but I’m actually addressing a different set of issues.</p>
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<p><span id="more-2478"></span></p>
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<p>For historical background, see Wikipedia on telos or <a href="http://en.wikipedia.org/wiki/Final_cause#Final_cause">final cause</a>.</p>
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<p>To understand why teleology matters, it helps to remember that human beings are prone to project intentions on everything. We are animists by instinct. Our religions and our folklore are full not merely of gods, angels, devils, and elves but talking trees and rocks as well. We need to think clearly about intention, purpose and design not so much to see it where it is but in order to avoid imputing it where it is not.</p>
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<p>Applying the language of purpose and intention to human beings, animals, and hypothetical other beings that we suppose to have desires has never been controversial. Human action has teleology; humans want to satisfy desires, and the anticipated future state of satisfaction is a cause of behavior in the past of that state.</p>
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<p>Nor is it controversial to apply teleological language to human artifacts. We may say, for example, that a firearm has the purpose of firing bullets or an airfoil has the purpose of generating lift without supposing that inanimate objects have intentions. What is relevant is that these functions express the designer’s intention for the artifact. I will call this “teleology of the first kind”.</p>
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<p>We perceive somewhat more difficulty applying the language of purpose and intention to natural systems that lack an obvious designer. What do we mean when we say that the purpose of the nectar in a flower is to attract bees? Is it at all meaningful to say that a flower intends to attract bees?</p>
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<p>If you are a creationist, then the nectar in a flower can have purpose in the same way that an airfoil or a firearm can have purpose; that is, as an expression of purpose in the mind of a designing God. But if you are doing philosophy, creationism is a self-destroying position; when anything can be explained by the action of a (causeless, inscrutable) God, philosophy dies because there is no point in causal accounts or explanatory theory at all. The moment anyone says “miracle”, it’s game over.</p>
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<p>So we’re left with a much more pointed question: is it ever meaningful to say that natural systems have purposes or intentions – teleology – in the <em>absence</em> of a designer? Intuitively, we feel that it is reasonable to say that the nectar in a flower has the purpose of attracting bees because the flower and the bees behave as though the flowers had been designed to attract bees, even if we can’t identify a designer. We have less tendency to attribute intentions to a flower because, outside of mythology, we don’t think of flowers as having mental lives.</p>
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<p>Historically, a school of so-called “natural theology” inferred a designer from the purpose of attracting bees. But, even if you could ignore the many internal problems with this position (starting with the one I pointed out in my next-to-previous paragraph) Charles Darwin pretty much killed natural theology stone-dead more than a century ago by inventing what I’ll call “teleology of the second kind”.</p>
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<p>Darwin said: Competing replicators are selected under pressure, and adaptation produces design without a designer. The nectar in a flower has the purpose of attracting bees because flowers that spread their pollen more effectively have more descendants, and attracting bees are an effective tactic which genetic lines of flowers have been competing to learn for millions of years. </p>
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<p>This one huge final cause in biology – that which replicates, survives – substitutes for a designer and separates teleology from design. It becomes a driver of behavior that can be usefully described as purposive all through biological systems. This account kills “natural theology” because it has more explanatory power than natural theology and proceeds from a premise that is both simpler than the existence of God and actually testable. We can observe evolution in action at many scales.</p>
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<p>All this is old news to anyone who has thought seriously about the philosophical implications of evolutionary theory. But now I enter new ground, because as an ex-mathematician I consider “two” to be a suspicious and unstable number. This suggests a simple question which as far as I’m aware no one has broached before: might there be a <em>third</em> kind of teleology?</p>
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<p>That is: are there natural systems in which the most natural description of behavior includes “purpose” or “intention”, but the driver is neither design nor Darwinian selection? Somewhat to my own surprise, I realized a positive answer within minutes of formulating the question. Not only that, I can identify the answer with a specific term in an equation of physics.</p>
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<p>First, an example. Trap about a centimeter thickness of water between two horizontal parallel glass plates. Apply uniform heat to the lower plate. If you watch, you’ll see the same increasing roiling and turbulence you’d get in a conventional tea kettle – except that past a certain critical temperature the turbulence abruptly disappears, and the water forms a regular, honeycomb-like array of hexagonal convection cells. </p>
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<p>Order – order that looks designed – has spontaneously appeared from turbulent chaos. What’s going on here?</p>
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<p>In the language of intention and purpose, the water “wants” to shed heat as rapidly as it can. At a certain temperature, it needs to form convection cells to do so. This is like the macroscopic order found in an artifact or an evolved adaptation, but the final cause is neither design nor Darwinian selection; rather, it’s the Second Law of Thermodynamics.</p>
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<p>The physical causation seems to work like this: randomly occurring convection micro-cells shed heat faster than neighboring chaotic regions and expand. The size of the resulting macro-cells is determined by the radius and depth that maximizes flow rate. Because the water is isotropically uniform, equal forces acting on all cells, you get a regular hexagonal close-pack – the most efficient (minimum-energy) tesselation. (In a real experimental setup of finite size, there will be distortions and broken cells at the edges).</p>
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<p>This kind of spontaneous order was explained in a more general way by a physical chemist named Ilya Progogine in the 1970s. What he discovered is that in thermodynamic systems far out of equilibrium, the tendency to remain disorderly may be overwhelmed by the tendency to dissipate heat as fast as possible. Such systems may spontaneously develop a dissipative macroscopic organization that looks purposive. Another well-known example is the <a href="http://en.wikipedia.org/wiki/Belousov%E2%80%93Zhabotinsky_reaction">Belousov-Zhabotinsky reaction</a>. </p>
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<p>This is teleology of a third kind, neither designed nor Darwinian. Prigogine showed that it corresponded to an additional term in the equations of thermodynamics that is zero or unobservably small near equilibrium. For this he got a Nobel Prize in 1977, and well deserved it.</p>
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<p>Are there more kinds of teleology? I haven’t thought of any. But it’s an interesting question, isn’t it?</p>
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