Conjectures and refutations

Karl Popper is probably the most famous name in philosophy of science, and is oft en invoked by scientists when they want to label some theory “pseudo-scien- tifi c”. I shall very briefl y outline his philosophy of science here, before moving on to the specifi cally evolutionary aspect of his views.

Popper proposed a solution to the problem of induction. First formulated by David Hume ([1739–40] 1978: bk I, pt III, §II), the problem of induction is this: suppose you have seen a thousand swans, all of which have been white. Is it rational to infer from this that all swans are white? Hume says no, because what you have seen only tells you that all the swans you have seen were white. It is invalid to infer from this that “all swans are white”. Just in case it is not obvious why, think of a deductive inference: all men are mortal, Socrates is a man, therefore Socrates is mortal. What makes this a valid inference is that if the premises are true the conclusion must also be true. However, as Hume pointed out, this is not the case with an inductive inference. Even if every swan you have seen is white, it could still be the case that not all swans are white. Hume concluded that induction is fundamentally non-rational; it is just a habit or instinct that we have.

Popper’s solution was to point out that, although we cannot prove a universal claim true by means of examples, we can prove one false by means of examples. For example: swan X is black, therefore not all swans are white. Th us, rejecting a universal claim could be rationally justifi ed. Popper wanted to show that, contra Hume, science, and indeed everyday thinking in general, could be rational. He rightly perceived that in both science and everyday life we make universal gen- eralizations: water boils at 100 °C at 1 atmosphere pressure; light always travels at 299,792,458 metres per second in a vacuum; apples are edible; wasps sting. If we tried to get along without such generalizations, we would have extremely impoverished science, and lives. Since we can only be rationally justifi ed in rejecting a universal generalization, what we should do is make generaliza- tions and hold on to them until they have been falsifi ed. Th is argument gave rise to Popper’s famous falsifi cationist criterion for separating real science from pseudo-science: real science makes falsifi able claims, pseudo-science does not.

Th e demarcation issue need not detain us here: what I am concerned with is Popper’s claim about how knowledge actually develops, and how he thinks that can be shown to be, at least when it is done properly, a rational process. 1

According to Popper, in both science and everyday life we habitually make “bold conjectures”, that is, we make hypotheses that are falsifi able. A child may make the bold conjecture “if I put my hand in the fi re, nothing bad will happen”. She may test it, and fi nd very quickly that it is false. Or she may make the bold conjecture “if I make the sound ‘bikkie’, mummy will give me one of those round, tasty things”. She may test it, and get a biscuit, but this does not prove the conjecture is true; it only fails to prove it is false. On Popper’s terminology, the second hypothesis has been corroborated. Th e child says to herself “so far, so good” and provisionally accepts the hypothesis as true. Later, she may make the sound “bikkie” and not get a biscuit. When this happens, she might try a diff erent bold conjecture “if mummy is frowning when I make the sound ‘bikkie’ she will not give me one, but if she is not she will”. Th is can then be tested and corroborated or falsifi ed. In this way, we continuously replace hypotheses about the world with new ones. Th e new ones are better because we have eliminated errors. Th us, according to Popper, knowledge progresses.

Popper explicitly calls this theory of knowledge an evolutionary one, and elaborates on the parallel with biological evolution in Chapter 7 of Objective

Knowledge (1979). Th e analogy between the above account and natural selection seems clear enough. Organisms are well adapted because they have survived the vicissitudes of life that could kill them or prevent them from reproducing. Natural selection is a continuous process of eliminating designs in favour of better ones. Our beliefs, according to Popper, are good because they have sur- vived the vicissitudes of experience that could prove them false. Th e develop- ment of knowledge is a continuous process of eliminating hypotheses in favour of better ones. Moreover, one of the consequences of Popper’s view is that it does not matter how a theory originates; all that matters is that it can stand up to the test of experience. Th is can be seen as analogous to the Darwinian claim that mutations are random; all that matters is that the new features produced can stand up to the test of living. In principle, a complete scientifi c novice could come up with a new, good, theory. All that makes this unlikely is that the demands that a theory has to meet are very stringent. Similarly, in principle a mutation could produce a new, adaptive, trait. All that makes that unlikely (remember that by Darwin’s logic most mutations are either harmful or make no diff erence) is that the demands that an organism has to meet are very strict. In both cases, what counts is not how a new theory/trait originates; what counts is how it stands up to tests. Th e process of generating new theories/traits does not have to be in any way directed. It is the continuous weeding-out of bad traits that guarantees the adaptedness of an organism. It is the continuous weeding- out of bad theories that guarantees the progress of science.

Tempting though the analogy is, however, it falls down on some points. Th e last sentence in the previous paragraph contains a clue to one of the problems.

Progress in science presumably means getting closer to the truth. Even though

Popper thinks we will never be able to say that we have reached the fi nal theory (even if we had a science that was completely true and comprehensive, how could we know this?), he thinks that newer ones are closer to the truth than older ones, in that they have eliminated the errors of the older ones. But, pre- sumably, this is supposed to mean objectively closer to the truth. For example, Popper would not claim that Ptolemaic astronomy was true in the middle ages but not in our time; he would say it was false at all times. Th e knowledge that we seek is timeless knowledge. If we are to talk of progress, we at least want to say that science is getting better by some universal standard. By contrast, a creature that is well adapted to one environment may be badly adapted to another environment. Two creatures may be completely diff erent, but both well adapted. We should not think of evolution as progressive in the strong sense of leading towards outcomes that are objectively, universally better. Some evo- lutionists claim that it is progressive in milder senses: that there are long-term trends towards greater complexity, for example (think of Williston’s law). But even if that is so, we can still only speak of creatures being adapted to specifi c circumstances. Th ere is no such thing as being “objectively”, timelessly, well adapted. If our view of the development of knowledge was to be analogous to evolution, we would have to be relativists, that is, we would have to say what is true at one time and place is false at another, and vice versa. Popper abhorred this kind of relativism.

Th ere is also a problem with the analogy between the falsifi cation of hypoth- eses and the elimination by natural selection of organisms, traits, species or whatever. Bear in mind that Popper wants to show that preferring one hypoth- esis over another can be rationally justifi ed. Science progresses not just because theories are falsifi ed, but because they are rightly judged to have been falsifi ed, and consequently rationally rejected. By contrast, the elimination of something by natural selection can be explained by completely blind, mechanical forces. To be analogous to natural selection, the rejection of theories would have to be something that happens even without there being rational grounds for it. It is true, and Popper accepts, that the history of science does not always conform to his idealized picture. A theory may be rejected rationally because it has been falsifi ed, or it may be rejected irrationally for any number of reasons. Perhaps the person who proposed it is not part of the scientifi c establishment, or is not good in public debates. Or perhaps the theory is off ensive to many people. Both the rational rejection and the irrational rejection may be considered to be cases of the theory failing because it is not adapted to its particular environment. Th at environment may include an ideally rational scientifi c community, but it may also include prejudices against certain people, or unwillingness to accept views

that are deemed off ensive. But Popper wants to distinguish between these two types of cases. Th e analogy with natural selection does not give us any basis for doing so.

As an attempt to answer the questions “What can we know?” and “How is it possible that we can have knowledge?”, Popper’s account is disappointing. If the analogy with natural selection was the whole story about how knowledge develops, then we would have to say that there is no such thing as an objectively true theory, and that theories just come and go for many diff erent reasons. Some people (e.g. Richard Rorty) do hold this view, but it was anathema to Popper. Popper wants to give an account that shows how we can be objectively right in our choice between two theories. But, if the analogy with natural selection is to be taken seriously, his account fails to do so.

Moreover, there is reason to believe that his account of how we build up knowledge is empirically false. According to Chomskian linguistics, cognitive science and evolutionary psychology, even very young children already have many presuppositions about the way the world is. Chomsky claims that we have inbuilt knowledge of the rules of universal grammar; and it seems well established that we have presuppositions about how physical objects behave, and many other things. Some of these inbuilt presuppositions may be false, but either way they are oft en highly recalcitrant to change in the light of experience. Th is does not seem to fi t in with Popper’s picture of a person generating and testing bold conjectures. I shall return to the subject of evolutionary psychol- ogy in Chapter 13.