Survival of the thickest?

I recently came across a novel argument by Alvin Plantinga, which aims to show that it is irrational for a human to believe both in naturalism and the theory of evolution by natural selection. Unfortunately, Plantinga never managed to write it up properly, but a draft may be found here. It is only worth reading the first part; the rest consists of a turgid and incomplete response to some objections which differ greatly in character from that which I give below. Essentially, Plantinga argues that evolution is unlikely to produce rational creatures whose reasoning is reliable: This gives those who believe that they are the result of unguided evolution a reason to doubt the reliability of their own reasoning, and so to doubt all of their conclusions; in particular they should doubt their belief in evolution.

Plantinga does not query the idea that natural selection can produce rational creatures. Instead, he aims to show that rational creatures arising in this way are unlikely to reason reliably; that their beliefs are likely, on the whole, to be false. It is necessary to introduce the idea of rationality in this way in order to make the argument apply to us. Evolution produces a great diversity of creatures, but we are the only rational creatures on Earth.

Since selection occurs on the basis of behaviour, Plantinga considers four possible ways in which the beliefs of a rational creature could be related to its behaviour.

1. Not at all. In this possibility, beliefs have no effect at all on behaviour. So true beliefs are no more likely to be selected for than false ones. Natural selection is unlikely to produce creatures with such useless baggage. Also, we would have no way to recognise that creatures of this kind were rational. We have no way of knowing that, for example, trees are not rational in this way. Since a key starting point of the argument was that we are the only rational creatures on Earth, the word rational must be being used in some sense that excludes this possibility. Humans are recognisably rational; it is ridiculous to think that our beliefs do not affect our behaviour.
   
2. Beliefs do affect behaviour, but in a way unrelated to their content. The same comments apply to this possibility as to the first.
3. Beliefs are causally efficacious: The creatures act on the basis of their beliefs. However, the behaviour this produces is maladaptive. Such creatures would die out. The probability of rational creatures produced by natural selection being of this kind is therefore tiny. Equally, our own continued survival as a species shows that we are not of this type.
   
4. Beliefs are causally efficacious: The creatures act on the basis of their beliefs. What's more, the behaviour that this produces is adaptive, so that the creatures survive. By a process of elimination, we are of this type. This is a good sign, since any rational creature produced by natural selection is overwhelmingly likely to be of this type.
   

Plantinga claims that the first two types of rationality would be fairly probable, a claim which the above analysis shows to be incorrect. He agrees that the third case is improbable. We can therefore focus in on the fourth case, where he claims that the probability that the beliefs of the creatures are, on the whole, reliable is not much more than 1 in 2. After all, it is possible to conjure up scenarios in which a creature survives by acting on the basis of false beliefs. To quote him:

Perhaps Paul very much likes the idea of being eaten, but when he sees a tiger, always runs off looking for a better prospect, because he thinks it unlikely that the tiger he sees will eat him. This will get his body parts in the right place so far as survival is concerned, without involving much by way of true belief. Or perhaps he thinks the tiger is a large, friendly, cuddly pussycat and wants to pet it; but he also believes that the best way to pet it is to run away from it. . . . or perhaps he thinks the tiger is a regularly recurring illusion, and, hoping to keep his weight down, has formed the resolution to run a mile at top speed whenever presented with such an illusion; or perhaps he thinks he is about to take part in a 1600 meter race, wants to win, and believes the appearance of the tiger is the starting signal; or perhaps. . . . Clearly there are any number of belief-cum-desire systems that equally fit a given bit of behavior.

Plantinga acknowledges that most such scenarios involve creatures whose belief-desire structures are, on the whole, maladaptive; they are only appropriate in very special circumstances. He therefore introduces a more subtle scenario. In this scenario, the creatures believe that everything is conscious, so that for example they have no word for 'tree', but rather one for 'conscious tree'. In particuar, almost all beliefs of the creature are false. This is, of course, a simplification of what early humans believed.

Suppose we were to meet such a creature, who spoke a different language to us. Let us suppose that their word for 'conscious tree' is 'shrubbery'. We, after talking to them for a while, would conclude that their word 'shrubbery' meant tree, and that their beliefs about trees were on the whole correct, but that they also had a false belief; namely, that trees are conscious. But any account of beliefs that accords with the way we use the word (to account for something which humans express by their language) must be such that in this case the beliefs of the beings are on the whole true, as we see, but that they include the false belief that everything is conscious.

This shows that Plantinga is simply working with an inadequate notion of what a belief is. That is fair enough; after all, we don't (as far as I know) have a good working definition to which he could refer. Nor can I give one. This unfortunately leads to incorrect arguments being put forward from time to time, of which Plantinga's is an example.

We may, however, say that we would expect some of the beliefs of the beings to be false. For example, it seems to be better to believe that there are causal links in situations where there are not than to risk missing actual causal links. So we would expect evolved rational beings to believe in causal links where there are none. We can easily observe that this is true of ourselves; it is called superstition. The field of studying what errors evolved beings might be expected to make is a growing one.

On the whole, we have found that we make errors of the expected kinds, and so this endeavour allows us to clear up our thinking. For example, those who understand some of this often actively guard against their tendency towards superstitious thinking. A sensible study of the limitations we would expect to find in ourselves given that we have evolved leads to humility, and to hope that understanding the truth about ourselves may yet set us free, but it does not swamp us in the kind of radical doubt Plantinga envisages.