10/23/2006

On the Darwinian explanation of the success of science

I really don't have time to post now, but I'm going to anyway. Van Fraassen writes: "I claim that the success of current scientific theories is no miracle. It is not even surprising to the scientific (Darwinian) mind. For any scientific theory is born into a life of fierce competition, a jungle red in tooth and claw. Only the successful theories survive--the ones which in fact latched on to actual regularities in nature." (Scientific Image, p.40)

James Robert Brown, in "Explaining the Success of Science" (Ratio, 1985) agrees that this Darwinian explanation can account for the first two aspects of success, but not the third:
(1) The sciences "are able to organize and unift a great variety of known phenomena.
(2) This ability to systematize the empirical data is more extensive now than it was for previous theories.
(3) A statistically significant number of novel predictions pan out; that is, our theories get more predictions right than mere guessing would allow." Brown says of (3): "Here the Darwinian analogy breaks down since most species could not survive a radical change of environment, the analogue of a novel prediction."

First a small point: I don't think a novel prediction needs to be analogized to a radical change in environment -- perhaps some should be, but it's not necessary. If an organism can handle living and reproducing in any new environment, i.e., one for which its various features were not historically adapted, then that seems a decent enough analogy to a novel prediction (which makes a prediction different from the cases the thoery was originally designed to handle). A 'radical' change in environment might precipitate a scientific revolution -- i.e., the science (like the organism) might not survive.

Now, a more substantive point, and one which perhaps pushes the analogy farther than is fair. The paleobiologist David Jablonski has shown that genera that are more geographically widespread are more likely to survive mass extinction events (such as the meteor that killed off lots of the dinosaurs). The analogy would be, I suppose, to groups of related theories that 'organize and unify' a greater variety of phenomena -- which are precisely the groups of theories that we (including van Fraassen) count as most successful. So it appears that a van Fraassenite Darwinian has a nice answer to J.R. Brown: viz., the more successful groups of theories will be more likely to deliver novel predictions.

But unfortunately for the van Fraassenite, the biological story doesn't end there. What is strange about Jablonski's results is that a species' being geographically widespread has no statistical correlation with its probability of surviving a mass extinction event. The correlation only appears at the level of genera. (Side note: For the philosophers and biologists who think about group selection, this looks like an instance of it.) So, the analogy would go, the more unifying particular theories do not enjoy any advantage in novel prediction over the less unifying, but the more unifying groups of theories would. Hopefully you can see why I suggested that this may be pushing the analogy too far: I'm not sure there's anything in the domain of science that would correspond nicely to the concepts of genus and species in the evolutionary domain. Although (and now I'm really stretching), if one could be made out, perhaps the structural realists could cash out their notion of structure at the level of the genus, and thereby capture why particular theories come and go, but the structure tends to survive through revolutions.

p.s. -- Can anyone recommend a good article completely devoted to arguing for or against this Darwinian explanation of science's success? I've seen several parts of book chapters or parts of papers dealing with it, but I can't recall seeing a fine-tooth-comb analysis of it.

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10/07/2006

Aristotle's natural motion and modern inertial motion

Last week, in my history of science class, we finished the unit on ancient science and medicine. At the end of the unit, I asked my students the (ill-posed) question: so is any of this stuff we've been reading science or not? (We read Plato's Timaeus, Aristotle's Physics II and On the Heavens, Ptolemy's Almagest, and bits of Epicurus as well as Hippocratic writers.)

One sentiment that came to the fore was that the ancients were (on average) more willing to countenance teleological explanations in natural sciences than we are. I think this is definitely right on the whole. But I did want to ask a question about an example sometimes forwarded in defense of this claim. Aristotle says that part of what makes the element earth earth is its tendency to move towards the center of the universe (since Aristotle thought the planet Earth was at rest in the center of the universe). Air and fire move away from the center of the universe, and the celestial matter moves in a circle around the center. These 'natural motions' are taken to appeal to final causes in a way that modern science does not: water and earth have a 'goal' or 'end' (Greek telos), viz., the center of the universe. And (so the story goes) matter from the Early Modern period onwards, starting with Descartes at the latest, is not like that at all.

I, unfortunately, cannot make out a substantive difference here -- we can describe Aristotle and the moderns in the same terms: we can make Aristotle sound more modern, or make Newton et al. sound more teleological. In the modern dynamical picture, we have inertial motion: a body in motion will maintain that motion (speed and direction), unless acted upon by an outside force. If the telos of an Aristotelian hunk of earth is the center of the universe, the telos of a modern bit of matter is (something like) self-preservation. Its goal is resistance to change (of direction and speed).

Alternatively, we can characterize Aristotle as more modern: Aristotle is describing what happens to a bit of fire or water if it's just "left alone," i.e., what does a body do when it is free of any interference? Aristotle clearly disagrees with the moderns about what a body does when "left alone"... but Einstein disagreed with Newtonians over the same issue. In other words, we can think of the difference (on this topic) between Aristotle and the moderns as a disagreement over which trajectories are the ones bodies will follow when no external forces act upon them. Teleology doesn't appear here at all.

Of course, I could be overlooking something obvious in the Aristotelian text. Hopefully any real Aristotle scholars out there reading this will tell me if I have. If you want to check the text of On the Heavens for yourself, it’s online here.

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