Molecular Evolution and Information

Life uses the equivalent of a four sided coin. To imagine this coin, visualize a playing die. Instead of numbers on each side, each side has a single letter. The letters are A,T,C and G. Since dice have 6 sides, this die has to be modified. This is easy to do. Imagine a long pin inserted into one side and out the other. This pin only allows the die to land on the 4 sides with letters. See figure 3.3.

Figure 3.3: Four Sided Die (Coin) with the Letters A, T, G, and C





    If this altered die is used as money, then it is just as good as any other 4 sided coin. But now instead of each coin having two possible outcomes, head or tails, each coin has 4 possible outcomes, A, T, G and C. Thus, each coin now contains 2 bits of information because 2² =4 (equation 1, p24).
    If these special coins are grouped three at a time, how many possible outcomes are there? Each coin contains 2 bits of information. Thus, 3 coins must contain 6 bits (2+2+2=6). There are now 64 possible outcomes because 2⁶ =64. This means that life could potentially have at its disposal 64 words, but life only needs 20 words. So some outcomes are assigned the same word.

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