Natural Selection and Evolution

Natural Selection Limits Tries

In the proceeding analysis, the effects of natural selection were ignored. To understand how natural selection affects the results consider the following example. Suppose the trapped scientist is now in a two-story building. The computer starts with a message already in it, and this message contains the knowledge to open all of the doors on the first story.

     The combination is dog-computer-cat-cat-bike-book-book-run-man-sun-dog-dog. The scientist is given two baskets. One contains 20 blocks labeled with words, and the other contains 12 blocks labeled with the numbers 1 through 12 (figure 15.8).

Figure 15.8: Natural Selection Preserves Existing Genes

The scientist is instructed to draw one block from each basket. He is to use the number that he draws to locate a position in the door’s combination, and he is to change the existing word at that position to the new word which he draws. For example, on the first try, the scientist draws the number 12 and the word cat. The original combination has the word dog at position 12. So the scientist replaces this word with the word cat. When he makes this change, the last door on the first floor slams shut because its combination is no longer correct. The scientist climbs down the ladder and realizes that he is trapped. He becomes very agitated. He changes the word cat back to dog, and the door opens.

       He leaves and refuses to participate in any further experiments. He has no desire to be trapped in the room, and his refusal to participate preserves the combination that opens the first floor doors.

        In this example, the combination that opens the doors on the first floor represents a gene, and the scientist represents natural selection. The scientist preserves this existing gene by refusing to participate in the experiment.

        If protein A is represented by the bottom doors, then this protein is preserved by natural selection. If the upper doors represent protein B, then this protein will not evolve. The reason is simple. The preservation of the combination that opens the first story doors prevents the top floor combination from being found.

   This example shows how and why natural selection preserves existing molecular knowledge.


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