If we suppose that the action of the human brain, conscious or otherwise, is merely the acting out of some very complicated algorithm, then we must ask how such an extraordinary effective algorithm actually came about. The standard answer, of course, would be ‘natural selection’. as creatures with brains evolved, those with more effective algorithms would have a better tendency to survive and therefore, on the whole, had more progeny. These progeny also tended to carry more effective algorithms than their cousins, since they inherited the ingredients of these better algorithms from their parents; so gradually the algorithms improved — not necessarily steadily, since there could have been considerable fits and starts in their evolution — until they reached the remarkable status that we (would apparently) find in the human brain. (Compare Dawkins 1986). (Penrose 1990: 414)

Even according to my own viewpoint, there would have to be some truth in this picture, since I envisage that much of the brain’s action is indeed algorithmic, and — as the reader will have inferred from the above discussion — I am a strong believer in the power of natural selection. But I do not see how natural selection, in itself, can evolve algorithms which could have the kind of conscious judgements of the validity of other algorithms that we seem to have. (Penrose 1990: 414)

Imagine an ordinary computer program. How would it have come into being? Clearly not (directly) by natural selection! Some human computer programmer would have conceived of it and would have ascertained that it correctly carries out the actions that it is supposed to. (Actually, most complicated computer programs contain errors — usually minor, but often subtle ones that do not come to light except under unusual circumstances. The presence of such errors does not substantially affect my argument.) Sometimes a computer program might itself have been ‘written’ by another, say a ‘master’ computer program, but then the master program itself would have been the product of human ingenuity and insight; or the program itself might well be pieced together from ingredients some of which were the products of other computer programs. But in all cases the validity and the very conception of the program would have ultimately been the responsibility of (at least) one human consciousness. (Penrose 1990: 414)

One can imagine, of course, that this need not have been the case, and that, given enough time, the computer programs might somehow have evolved spontaneously by some process of natural selection. If one believes that the actions of the computer programmers’ consciousness are themselves simply algorithms, then one must, in effect, believe algorithms have evolved in just this way. However, what worries me about this is that the decision as to the validity of an algorithm is not itself an algorithmic process! … (The question of whether or not a Turing machine will actually stop is not something that can be decided algorithmically.) In order to decide whether or not an algorithm will actually work, one needs insights, not just another algorithm. (Penrose 414-415)

Nevertheless, one still might imagine some kind of natural selection process being effective for producing approximately valid algorithms. Personally, I find this very difficult to believe, however. Any selection process of this kind could act only on the output of the algorithms and not directly on the ideas underlying the actions of the algorithms. This is not simply extremely inefficient; I believe that it would be totally unworkable. In the first place, it is not easy to ascertain what an algorithm actually is, simply by examining its output. (It would be an easy matter to construct two quite different simple Turing machine actions for which the output tapes did not differ until, say, the 2^65536th place — and this difference could never be spotted in the entire history of the universe!) Moreover, the slightest ‘mutation’ of an algorithm (say a slight change in a Turing machine specification, or in its input tape) would tend to render it totally useless, and it is hard to see how actual improvements in algorithms could ever arise in this random way. (Even deliberate improvements are difficult without ‘meanings’ being available. This inadequately documented and complicated computer program needs to be altered or corrected; and the original programmer has departed or perhaps died. Rather than try to disentangle all the various meanings and intentions that the program implicitly depended upon, it is probably easier just to scrap it and start all over again!) (Penrose 1990: 415)

Perhaps some much more ‘robust’ way of specifying algorithms could be devised, which would not be subject to the above criticisms. In a way, this is what I am saying myself. The ‘robust’ specifications are the ideas that underlie the algorithms. But ideas are things that, as far as we know, need conscious minds for their manifestation. We are back with the problem of what consciousness actually is, and what it can actually do that unconscious objects are incapable of — and how on earth natural selection has been clever enough to evolve that most remarkable of qualities. (Penrose 1990: 415)

(….) To my way of thinking, there is still something mysterious about evolution, with its apparent ‘groping’ towards some future purpose. Things at least seem to organize themselves somewhat better than they ‘ought’ to, just on the basis of blind-chance evolution and natural selection…. There seems to be something about the way that the laws of physics work, which allows natural selection to be much more effective process than it would be with just arbitrary laws. The resulting apparently ‘intelligent groping’ is an interesting issue. (Penrose 1990: 416)

The non-algorithmic nature of mathematical insight

… [A] good part of the reason for believing that consciousness is able to influence truth-judgements in a non-algorithmic way stems from consideration of Gödel’s theorem. If we can see that the role of consciousness is non-algorithmic when forming mathematical judgements, where calculation and rigorous proof constitute such an important factor, then surely we may be persuaded that such a non-algorithmic ingredient could be crucial also for the role of consciousness in more general (non-mathematical) circumstances. (Penrose 1990: 416)

… Gödel’s theorem and its relation to computability … [has] shown that whatever (sufficiently extensive) algorithm a mathematician might use to establish mathematical truth — or, what amounts to the same thing, whatever formal system he might adopt as providing his criterion of truth — there will always be mathematical propositions, such as the explicit Gödel proposition P(K) of the system …, that his algorithm cannot provide an answer for. If the workings of the mathematician’s mind are entirely algorithmic, then the algorithm (or formal system) that he actually uses to form his judgements is not capable of dealing with the proposition P(K) constructed from his personal algorithm. Nevertheless, we can (in principle) see that P(K) is actually true! This would seem to provide him with a contradiction, since he ought to be able to see that also. Perhaps this indicates that the mathematician was not using an algorithm at all! (Penrose 1990: 416-417)

(….) The message should be clear. Mathematical truth is not something that we ascertain merely by use of an algorithm. I believe, also, that our consciousness is a crucial ingredient in our comprehension of mathematical truth. We must ‘see’ the truth of a mathematical argument to be convinced of its validity. This ‘seeing’ is the very essence of consciousness. It must be present whenever we directly perceive mathematical truth. When we conceive ourselves of the validity of Gödel’s theorem we not only ‘see’ it, but by so doing we reveal the very non-algorithmic nature of the ‘seeing’ process itself. (Penrose 1990: 418)