Эволюциялық ізденістер: «Даукинстің мысығы» және биоморфтар моделі

The weasel program or Dawkins' weasel is a thought experiment and a variety of computer simulations illustrating it. Their aim is to demonstrate that the process that drives evolutionary systems—random variation combined with non random cumulative selection—is different from pure chance. The thought experiment was formulated by Richard Dawkins, and the first simulation written by him; various other implementations of the program have been written by others.

In The Blind Watchmaker, Dawkins goes on to provide a graphical model of gene selection involving entities he calls biomorphs. These are two dimensional sets of line segments which bear relationships to each other, drawn under the control of "genes" that determine the appearance of the biomorph. By selecting entities from sequential generations of biomorphs, an experimenter can guide the evolution of the figures toward given shapes, such as "airplane" or "octopus" biomorphs. As a simulation, the biomorphs are not much closer to the actual genetic behavior of biological organisms. Like the Weasel program, their development is shaped by an external factor, in this case the decisions of the experimenter who chooses which of many possible shapes will go forward into the following generation. They do however serve to illustrate the concept of "genetic space," where each possible gene is treated as a dimension, and the actual genomes of living organisms make up a tiny fraction of all possible gene combinations, most of which will not produce a viable organism. As Dawkins puts it, "however many ways there may be of being alive, it is certain that there are vastly more ways of being dead". In Climbing Mount Improbable, Dawkins responded to the limitations of the Weasel program by describing programs, written by other parties, that modeled the evolution of the spider web. He suggested that these programs were more realistic models of the evolutionary process, since they had no predetermined goal other than coming up with a web that caught more flies through a "trial and error" process. Spiderwebs were seen as good topics for evolutionary modeling because they were simple examples of biosystems that were easily visualized; the modeling programs successfully generated a range of spider webs similar to those found in nature.

Although Dawkins did not provide the source code for his program, a "Weasel" style algorithm could run as follows. Start with a random string of 28 characters. Make 100 copies of the string (reproduce). For each character in each of the 100 copies, with a probability of 5%, replace (mutate) the character with a new random character. Compare each new string with the target string "METHINKS IT IS LIKE A WEASEL", and give each a score (the number of letters in the string that are correct and in the correct position). If any of the new strings has a perfect score (28), halt. Otherwise, take the highest scoring string, and go to step 2. For these purposes, a "character" is any uppercase letter, or a space. The number of copies per generation, and the chance of mutation per letter are not specified in Dawkins's book; 100 copies and a 5% mutation rate are examples. Correct letters are not "locked"; each correct letter may become incorrect in subsequent generations. The terms of the program and the existence of the target phrase do however mean that such 'negative mutations' will quickly be 'corrected'.