I don't know who it was first pointed out that, given enough time, a monkey bashing away at random on a typewriter could produce all the works of Shakespeare. The operative phrase is, of course, given enough time. Let us limit the task facing our monkey somewhat. Suppose that he has to produce, not the complete works of Shakespeare but just the short sentence 'Methinks it is like a weasel', and we shall make it relatively easy by giving him a typewriter with a restricted keyboard, one with just the 26 (capital) letters, and a space bar. How long will he take to write this one little sentence?More time, by a factor of millions, than the age of the universe. Dawkins next considers a model of cumulative selection:
...We again use our computer monkey, but with a crucial difference in its program. It again begins by choosing a random sequence of 28 letters, just as before ... it duplicates it repeatedly, but with a certain chance of random error – 'mutation' – in the copying. The computer examines the mutant nonsense phrases, the 'progeny' of the original phrase, and chooses the one which, however slightly, most resembles the target phrase, METHINKS IT IS LIKE A WEASEL....Dawkins observes that cumulative selection radically accelerates the 'evolution' of the phrase:
The exact time taken by the computer to reach the target doesn't matter. If you want to know, it completed the whole exercise for me, the first time, while I was out to lunch. It took about half an hour. (Computer enthusiasts may think this unduly slow. The reason is that the program was written in BASIC, a sort of computer baby-talk. When I rewrote it in Pascal, it took 11 seconds.) Computers are a bit faster at this kind of thing than monkeys, but the difference really isn't significant. What matters is the difference between the time taken by cumulativeselection, and the time which the same computer, working flat out at the same rate, would take to reach the target phrase if it were forced to use the other procedure of single-step selection: about a million million million million million years. This is more than a million million million times as long as the universe has so far existed.There's no question that cumulative selection- the retention of close calls to the target- speeds the convergence on the target.
Dawkins' METHINKS IT IS LIKE A WEASEL experiment has given rise to a lot of discussion.
There's no question that real evolution is cumulative, in the sense that adaptive change are collected and propagated in the genome. That's the whole point of heritable variation and natural selection. Evolution is to a target- adaptation- and in some situations (situations lacking irreducible complexity) partial adaptive improvements are preserved. Models of evolution need to reflect that fact of nature.
Yet I believe that Dawkins and his defenders misunderstand the weasel program. The weasel model argues strongly for the inference to teleology/design, not for undirected evolution.
1) Dawkins inadvertently and inescapably uses a model of design. The computer itself, the program, the endpoint are all designed by minds. Even the random letter generator is a meticulously designed program. But the essence of Darwin's theory is that there is no goal-directedness, no design, in evolution. So why would Dawkins use a model that is entirely designed? The reason is obvious: he has no choice. Design permeates nature.
2) The teleology in Darkins' weasel program is particularly in the target. The teleology permeates the system, but the crucial teleology is the adaptation- the match between the 'random' process and the environment.
This observation has been made by ID theorists, most notably Bill Dembski. It is not necessary to see the design as put into the system as a (figurative) hand coming down out of the clouds and tinkering with the genes to make the organism better adapted. The intelligence in nature is in the match between the variation and the environment. The intelligence is in the fit, the adaptation itself, not just in the organism or just in the environment.
Dawkins' weasel program is a nice simulation of intelligent design.