What Mad Pursuit by Francis Crick Read Free Book Online

the future. It has no vision, no foresight, no sight at all. If it can be said to play the role of watchmaker in nature, it is the blind watchmaker.
    Dawkins gives a very pretty example to refute the idea that natural selection could not produce the complexity we see all around us in nature. The example is a very simple one, but it drives the point home. He considers a short sentence (taken from Hamlet ):
    METHINKS IT IS LIKE A WEASEL.
    He first calculates how exceedingly improbable it is that anyone, typing at random (traditionally a monkey, but in his case his eleven-month-old daughter or a suitable computer program) would by chance hit on this exact sentence, with all the letters in their correct place. [The odds turn out to be about 1 in 10 40 .] He calls this process “single-step selection.”
    He next tries a different approach, which he calls “cumulative selection.” The computer chooses a random sequence of twenty-eight letters. It then makes several copies of this but with a certain chance of making random mistakes in the copying. It next proceeds to select the copy that most resembles the target sentence, however slightly. Using this slightly improved version, it then repeats this process of replication (with mutation) followed by selection. In the book Dawkins gives examples of some of the intermediate stages. In one case, after thirty steps, it had produced:
    METHINKS IT IS LIKE A WEASEL
    and after forty-three steps it had the sentence completely correct. How many steps it takes to do this is partly a matter of chance. In other trials it took sixty-four steps, forty-one steps, and so forth. The point is that by cumulative selection one can reach the target in a relatively small number of steps, whereas in single-step selection it would take forever.
    The example is obviously oversimple, so Dawkins tried a more complex one, in which the computer grew “trees” (organisms) according to certain recursive rules (genes). The results are too complex to reproduce here. Dawkins says: “Nothing in my biologist’s intuition, nothing in my 20 years’ experience of programming computers, and nothing in my wildest dreams, prepared me for what actually emerged on the screen” (p. 59).
    If you doubt the power of natural selection I urge you, to save your soul, to read Dawkins’s book. I think you will find it a revelation. Dawkins gives a nice argument to show how far the process of evolution can go in the time available to it. He points out that man, by selection, has produced an enormous variety of types of dog, such as Pekinese, bulldogs, and so on, in the space of only a few thousand years. Here “man” is the important factor in the environment, and it is his peculiar tastes that have produced (by selective breeding, not by “design”) the freaks of nature we see preserved all around us as domestic dogs. Yet the time required to do this, on the evolutionary scale of hundreds of millions of years, is extraordinarily short. So we should not be surprised at the ever greater variety of creatures that natural selection has produced on this much larger time scale.
    Incidentally, Dawkins’s book contains a fair but devastating critique (pages 37-41) of the book The Probability of God by Hugh Montefiore, the Bishop of Birmingham. I first knew Hugh when he was Dean of Caius College, Cambridge, and I agree with Dawkins that Hugh’s book “… is a sincere and honest attempt, by a reputable and educated writer, to bring natural theology up to date.” I also agree wholeheartedly with Dawkins’s criticism of it.
    At this point I must pause and ask why exactly it is that so many people find natural selection so hard to accept. Part of the difficulty is that the process is very slow, by our everyday standards, and so we rarely have any direct experience of it operating. Perhaps the type of computer game Richard Dawkins describes might help some people to see the power of the mechanism, but not everyone likes to play