Reducing Biology to Physics

A little exchange over at The Curious Wavefunction that I thought I’d reproduce here.

I didn’t take the time to discuss different varieties of reduction. I’m mostly thinking of metaphysical supervenience in my response, which I think is fair since Wavefunction specifies that s/he is interested in ontology not epistemology.

There are, of course, denials of reduction coming from nonreductive physicalists that are supposed to be compatible with supervenience, but it doesn’t seem to me that Wavefunction has any of these in mind (but perhaps I’m wrong).

A common claim is that higher level causal powers cannot be reduced to lower-level physical causal powers, but this claim is (mostly) wrong. That’s for another day, however. For now, here’s my comment over there.

Wavefunction argued that a Laplacian demon (or a “superfreak” to use a term from the Bernstein review that introduces the post) who knows all the laws of physics would be unable to predict the existence of giraffes because biological details depend on historical accidents. Wavefunction takes this to show that biology is not reducible to physics.

My reply:

If physics is deterministic (so let’s suppose that a nonlocal hidden variable interpretation of quantum mechanics is correct), and if our superfreak (or Laplacian demon, as the more traditional account has it) knows the complete physical state in addition to all the laws (and has an unlimited computational capacity), then the superfreak will be able to predict the existence of giraffes and every other biological detail.

Leaving out relevant physical details (i.e., the initial conditions) does not not show that biology is non-physical. Of course, it is true that physical dynamics alone will never tell us what sort of creatures evolve and which don’t, but why would we ever think it might? Mere physical laws can’t even tell us that there will be protons and neutrons.

And a follow up:

Curious Wavefunction says:

If we can truly reduce biology to physics, it must mean that we should be able to . . . construct the present biological world starting from the basic laws of physics.

Again, this form of “reduction” is just a non-starter. If you insist that we only have reduction when the laws (and only the laws) specify some feature of the world, then nothing can be reduced (except the laws themselves).

The physical laws are compatible with the complete absence of matter, so the laws are never going to tell you whether there’s matter or a total vacuum.

The criterion for reduction that you’re using is unhelpful, because on this account nothing can be reduced to physics.

A much more useful account of reduction is one which asks whether we can predict some feature if we are given both the laws and the complete physical state (and unlimited computational power, since we’re interested in ontology not epistemology).

In this case, it seems clear that the Laplacian demon (superfreak) would predict the existence of giraffes (though the demon might not call them “giraffes”).

Even if the structure of the mammalian heart could be predicted in principle, it would be impossible to predict beforehand that the most important function of the heart among myriad others is to pump blood.

I know famous people like Fodor and Searle make this claim (I didn’t realize Kauffman did; I’ll have to look at his book at some point), but it’s just wrong:

(a) Even if we insist that one needs to know the evolutionary history of a trait to know its “real function,” the Laplacian demon would have all of that information available. It knows the complete history of the total physical state of the universe.

(b) If our demon (“superfreak”) is smart enough to care about which functions are “the most important” then it should have little difficulty recognizing that the function of the heart is to pump blood (even without peaking at the past). It would be able to recognize certain self-regulating processes that maintain themselves against the flows of entropy, and it would be able to recognize that the heart’s circulating blood is an important component of this self-sustaining process (whereas, for example, the sound the heart makes is not).

Now, if we stipulate that our demon is not allowed to care about any structure or order above the level of particles, then you’re right that the demon will be ignorant of biological facts. But with this stipulation, the demon would also be ignorant of the shape of planets, the temperatures of stars, the rigidity of ice, and so on and so on. But this just shows that we shouldn’t make such a stipulation if we’re trying to figure out the ontology of the world.


5 responses to “Reducing Biology to Physics

  1. I’m not sure about Laplacian daemons (can there be many?), but I’m quite sure Harvey did discover the proper function of mamelian hearts, which is to pump. If Fodor, Searle, or Kauffman have problems explaining Harvey’s discovery, they better have a good excuse. In fact, this makes me doubt that they hold that counterfactual:

    > Even if the structure of the mammalian heart could be predicted in principle, it would be impossible to predict beforehand that the most important function of the heart among myriad others is to pump blood.

    I know the answer for Searle should lie in a close reading of chapter 10 of The Rediscovery of the Mind, that I could do if you need. (Perhaps also Intentionality, or his discussion with Chomsky in BBS.) But it’s been too long since I’ve read Fodor. As to Kauffman, I’ve no idea.

    • The Harvey example is a good one; I might have to steal it. It is noteworthy that Harvey’s discovery predated Darwin by a century or two . . .

      I’ll look at how Searle formulates his argument sometime soon. If I recall, he claims that functions are always assigned by some conscious agent; there can be no objective (mind-independent) fact about which causal powers are “functions” and which are not.

      As I see it, his argument rests on a couple mistakes:

      1) A failure to pay sufficient attention to causal/dynamical facts.

      2) A failure to recognize that contextual/relational facts can be perfectly “objective” in the sense of not depending on consciousness.

      I may be speaking on this topic in a couple months, in which case I’ll definitely be brushing up on what exactly Searle says.

      • Oh, go right ahead and steal it: it’s from Searle himself, in the chapter quoted above.

        If you need to talk about Searle, you could take a look in The Construction of Social Reality, where he discusses proper functions. I can’t tell you more, as my copy is away from me for the moment.

        You could also look pages 58-59 of Making the Social World. No need to buy another book: I could send the relevant quotes to you.

        I do like the sound of your (2). But please bear in mind that his argument only rests on the claim that, for him, a function is an intensional concept, and that to say “X serves the function of Y” makes sense because we put some teleonomy (a “purpose”) at work. It would be easy to counter this claim by recitating the functionalist credo, but then you’d have to settle for a draw.

        Perhaps this is where your (1) comes into play?

      • I just ordered Making the Social World; I should make sure I’m up to date with my Searle. (Besides, one of these days I’m going to beat up on his account of free will too, and I see he’s got a chapter on the topic.)

        My copy of Construction of Social Reality is out at the office, so I can’t double-check at the moment, but does he appeal to intensionalitity-with-an-s or to intentionality-with-a-t? As I recall his argument (and as I see it in Rediscovery of the Mind), his core point is that it is only our interests that pick out something as a “function” as opposed to a “mere” cause.

        Intensionality-with-an-s is opacity under substitution of co-referring terms; which might be related, but I don’t recall Searle building an argument against functions on it. If he does, I’d wonder whether it’s related to Fodors (rather confused) argument against natural selection. Fodor claims that nature can’t select for particular traits (such as pumping blood), because there will also be various other coextensive traits (such as making thumping sounds), and since nature isn’t conscious, there’s no way there could be a fact of the matter about its selecting for pumping and not for thumping. A conscious agent could have one aspect in mind and not the other, but an unconscious process could make no such distinction. (At least I think this is the core of his argument.) It’s similar to Searle’s complaint, and worries about co-referring but non-synonymous terms are in the neighborhood.

        Anyhow, back to Searle: Here’s a bit more of my complaint.

        Searle says (ReDisc Mind p. 238), “[W]hen we say that the heart functions to pump blood, the only facts in question are that the heart does, in fact pump blood; the fact is important to us, and is causally related to a whole lot of other facts that also are important to us, such as the fact that the pumping of blood is necessary to staying alive. If the only thing that interested us about the heart was that it made a thumping noise or that it exerted gravitational attraction on the moon, we would have a completely different conception of its “functioning” and correspondingly of, for example, heart disease. To put the point bluntly, in addition to its various causal relations, the heart does not have any functions.”

        Now, I think he’s right that one important component of our notion of “function” is tied to our interests. But I think he’s far too quick to think that this exhausts our concept, and that if we strip away the subjective valuation that all causes need to be treated as ontologically on par with one another.

        Let’s be completely disinterested metaphysicians; all we care about is hard-core physicalist ontology (one of us might even adopt the name “Physicalist”), and we don’t give a hoot about good and bad or any values whatsoever (except the truth of our physicalist ontology).

        Will we now conclude that there is no important difference between the heart’s pumping blood and the heart’s making a thumping sound? We will indeed agree that it does in fact do both, but surely we will notice an important physical difference between the two effects.

        We will notice that the body is a very complex self-regulating system that is organized so as to be insensitive to many details of its environment but highly sensitive to some other details. It is highly constrained, so that a great number of molecules all move together over great distances. It is comparatively difficult to separate these molecules (the body doesn’t fall apart), and yet many of the molecular structures are themselves in complex relational motion. And so on. All of these are physical facts that are quite independent of our interests.

        And it is also a physical fact that the heart’s pumping blood is an essential component of the maintenance of this highly complex – robust, yet sensitive – process that is life. The system will (as a matter of physical fact) cease to continue maintaining its low-entropy state (at the expense of increasing the entropy in its environment) if the heart stops pumping. The pumping of blood is strongly causally correlated with a large number of other physical systems.

        On the other hand, the thumping of the heart has very little systematic effect on the other physical systems. If we were to silence the sound (while maintaining the other causal features of the heart) other nearby physical systems would be largely unchanged. Again, this is a simple physical fact that follows merely from the physical laws; our interests don’t matter.

        So, there is an objective, interest-free, fact about blood pumping being an essential part of a complex physical system, and about thumping sounds being irrelevant to the systematic behavior of any system whatsoever.

        I’d say this is a pretty important difference. Not all causes are equal.

        Is this enough to secure a “functional level of explanation”? I suppose it depends on what we want from such “functional” descriptions. But it seems to me that this systems-level notion of function is plenty robust to undergird a cognitivist account of consciousness. The interest-laden notion of “function” is something that can easily be jettisoned.

  2. Pingback: Reduction, Wavefunction, and Physics « Physicalism

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