“what it does”
10.2 Does biology have real laws?
Th roughout the previous section I have been assuming that neither ceteris
paribus laws nor truths by defi nition can be genuine laws. Moreover, I have
been assuming that the physical sciences – physics and chemistry – are in pos- session of genuine laws. However, it has been argued that such a picture of the physical sciences is unrealistic. Perhaps, contrary to what I have been assuming
so far, the laws of physics and chemistry are either ceteris paribus or true by defi nition aft er all.
A case has been made by Mark Colyvan and Lev Ginzburg (2003) that at least a great many of what we accept as the “laws of physics” are in fact ceteris paribus laws. As an example, they give Galileo’s law that “all massive bodies fall with constant acceleration irrespective of their mass”. As they point out, there are plenty of objects that do not conform to this law: hailstones, snowfl akes, para- chutists and so on. So the law is ceteris paribus only. Th ey anticipate the reply: but there are reasons why these cases do not conform to the law, which are well known. Snowfl akes and the rest are suffi ciently light that air resistance becomes a relevant factor in predicting their motion. Th e law, strictly speaking, only describes the eff ect of gravity on things, and therefore its predictions only come true if there is no other force involved. When there is no other force involved, it is true without exception. But Colyvan and Ginzburg reply to this that, in the case of many physical laws, the conditions they require are highly idealized, so that they are never in fact realized. Newton’s laws of motion predict that the planets will orbit the sun in ellipses, but in fact they only do so in approximate ellipses, because of the gravitational eff ect of other planets, among other factors. So perhaps there is nothing wrong with ceteris paribus laws. Many of the laws that philosophers of science take to be the best exemplars of what laws should be like – that is, the laws of physics – are ceteris paribus. So the ceteris paribus laws of biology are just as much laws as any other.
Martin Carrier (1995) makes a similar point, with reference to Galileo’s law. Th e fact that it has exceptions, he argues, should not be taken as meaning that it is not a law. Rather, it is a law that only applies when a specifi ed set of initial conditions is met. Th e initial conditions include or imply that air resistance is not also acting on the object. Properly construed, the law should be read as “all massive bodies fall with constant acceleration irrespective of their mass, pro- vided there is no wind resistance, and so on”. So the fact that snowfl akes and the like do not conform to the law does not stop it from being a law.
However, this argument may backfi re. What Carrier’s take on things sug- gests is that the law may actually be a strict, exceptionless aft er all, law and not a ceteris paribus law. Galileo’s law holds true (or is supposed to) when the only force operating on an object is the gravity of the body it is falling towards. Even if we conceded that this is never the case – that even a falling bowling ball is infl uenced to some tiny degree by the air it is falling through, or by the moon’s gravity, or any number of things – we could still say that, when the required conditions are met, the law applies without exception. We can say this even if the required conditions are never met, because we can at least imagine them being met. One might be tempted to think that the situation with Galileo’s law is the same as that with the proposed law of natural selection. Th ere is an open-ended list of things that might interfere with an object’s descent towards the ground: air
resistance, magnetic fi elds, passing birds and so on. Similarly, there is an open- ended list of things that might interfere with the level of fi tness increasing in a population under selection. We can summarize the list with the labels “chance” and “constraint”, but either of those terms can cover a multitude of possibilities. So, we might conclude, both laws are in the same boat, both being subject to an indefi nite number of possible interfering factors. However, the two cases are still not the same. We can imagine – and in fact we can even construct a mathemati- cally precise model of – a situation where nothing other than gravity acts on a body. We might be tempted to think that we can similarly imagine a situation where nothing but natural selection acts on a population. But can we?
Th e problem, I suggest, is that natural selection can only act where there is constraint. Th at is, not only is constraint always there, but it is impossible to conceive of natural selection taking place without it. Th is is, I suggest, for two reasons. First, to imagine a situation without constraint would be to imagine creatures with no constancy of structure whatsoever. We saw in Chapter 1 that heredity – that is, that off spring reliably resemble their parents to a high degree – is a necessary condition for natural selection. But this also constrains natural selection. Secondly, without constraint, there would be no situation to which creatures could become better adapted. I already argued this (albeit briefl y) at the end of Chapter 4. Put simply, a problem arises for a creature because of
both its environment and the way the creature is itself constituted. So the way
the creature is constituted partly determines what would count as becoming better adapted, or fi tter. But the way the creature is constituted also imposes constraints on how it can evolve. So, whereas we can imagine Galileo’s law operating without any interfering factors, we cannot imagine natural selec- tion operating without any interfering factors. Galileo’s law is exceptionless in that it applies in every situation where gravity is the only thing operating. Th e proposed law of natural selection, by contrast, cannot be exceptionless in this way, because the very idea of “nothing other than natural selection operating” makes no sense.
Sober (1984: ch. 2) proposes a diff erent approach to showing that there are real biological laws. Instead of trying to show that ceteris paribus laws can be real laws, he proposes that truths by defi nition can be real laws. As an example he off ers: water is H2O. He says much the same things about this as I said about salientiates above. Th e discovery that water is H2O was an empirical discovery, and could not have been made just by looking at the defi nition of the word “water”. But water is H2O by defi nition, in just the same way that every salienti-
ate shares a common ancestor with all and only salientiates by defi nition. Th at is, if we were to discover that some sample of a liquid was not H2O, then we would have discovered that it was not water, no matter how much it looked and behaved like water. So, Sober, argues, something can still be a law even if it is true by defi nition.
Th is point can be related (although Sober does not do this) to a more wide- ranging point made by W. V. Quine in his famous paper “Two Dogmas of Empiricism” (1961). Th roughout this discussion so far, I have been assum- ing that there is a diff erence between things that are true by defi nition, and things that are not. In philosophy this diff erence is commonly referred to as the analytic–synthetic distinction. As these terms are traditionally understood,
analytic truths are those that are true just in virtue of defi nitions: “all bachelors
are unmarried” is an example. Synthetic truths contain information that goes beyond what is contained in the defi nition: “John is a bachelor” is an example. One way in which one might clarify this distinction would be to say that in order to know that something is an analytic truth, all one needs to know is the defi ni- tion. One can know that “all bachelors are unmarried” is true just by knowing what the words in the statement mean. But one could not know that John is a bachelor this way: one would have to know some facts about the world – that is, whether or not John is married – in addition to knowing what the words mean. Quine, however, argued against this distinction. One way we can understand what Quine is saying is to look again at the statement “water is H2O”. On the
one hand, that water is H2O is something that had to be discovered, and could not have been determined just by knowing the defi nition of the word “water”. But on the other hand, if we found that something that looked just like water was not H2O, we would say it is not water, rather than that we have discovered
that some water is not H2O. So, what exactly happened when scientists accepted that water is H2O: was an empirical discovery made about water, or was the defi nition of the word “water” changed? We would surely have to answer: both. Th e defi nition of “water” changed, but because of empirical discoveries. So, Quine is urging, the neat distinction that we make between truths by defi nition and other kinds of truths cannot be made. But there is more still. Th ere could conceivably be some revolution in science in the future such that scientists no longer thought that the stuff we drink, swim in and so on was H2O. Th is would
mean that we would no longer say that anything that was water has to be H2O. Something that we now treat as true by defi nition would have turned out to be false. If we accept Quine’s claim, then, it does not matter whether biological laws turn out to be true by defi nition or not, for there is no real diff erence between a truth by defi nition and some other kind of truth.
Quine’s view is, admittedly, still controversial. Nonetheless, the upshot of our discussion of whether biology has laws may just turn out to be: it depends on what you mean by a law. If you agree with Quine, then something’s being true by defi nition is no obstacle to its being a law, since there is no clear distinction anyway. One does not have to go as far as Quine to agree with Sober, provided one thinks that something that is true by defi nition can be a law. If one does not agree with Sober on this, then one may have diffi culty, not just accepting biological laws, but accepting physical laws as well. I started this chapter by
remarking that philosophers of science tend to take the physical sciences as exemplary. If they are right, then biology needs to be either shown to be like physics in the relevant respects, or else accepted as being an inferior science. I want to argue against this in the next section: in other words, I want to argue that biology is diff erent in important respects from the physical sciences, but in no way inferior.