John Allen Paulos in his Who’s Counting? column at ABC News:
…the standard [creationists’] argument goes roughly as follows. A very long sequence of individually improbable mutations must occur in order for a species or a biological process to evolve.
If we assume these are independent events, then the probability of all of them occurring and occurring in the right order is the product of their respective probabilities, which is always an extremely tiny number.
Thus, for example, the probability of getting a 3, 2, 6, 2, and 5 when rolling a single die five times is 1/6 x 1/6 x 1/6 x 1/6 x 1/6 or 1/7,776 — one chance in 7,776.
The much longer sequences of fortuitous events necessary for a new species or a new process to evolve leads to the minuscule numbers that creationists argue prove that evolution is so wildly improbable as to be essentially impossible.
This line of argument, however, is deeply flawed.
More here. [Improbable photo shows Paulos with llamas in Peru.]