Since it was deciphered four decades ago, some have claimed that the genetic code must be a frozen accident, while others have argued that it was shaped by natural selection. A striking feature of the genetic code is its inherent resistance to the effects of mutation. For example, a change in the third position of a codon often specifies the same amino acid or one with similar chemical properties.

The natural code resists mutation more effectively (is less susceptible to error) than most other possible versions, as illustrated in Figure Q1–1. Only one in a million computer generated “random” codes is more error-resistant than the natural genetic code. Does the extraordinary mutation resistance of the genetic code argue in favor of its origin as a frozen accident or as a result of natural selection? Explain your reasoning.

Figure Q1–1

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20 15 10 natural code 5 10 15 20 susceptibility to mutation number of codes (thousands)