Ode to the Code

American Scientist ^ | November-December 2004 | Brian Hayes

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What's so special about the one code that -- with a few minor variations -- rules all life on Planet Earth? The canonical nonanswer to this question came from Francis Crick, who argued that the code need not be special at all; it could be nothing more than a "frozen accident." The assignment of codons to amino acids might have been subject to reshuffling and refinement in the earliest era of evolution, but further change became impossible because the code was embedded so deeply in the core machinery of life... There has always been resistance to the frozen-accident theory. Who wants to believe that the key to life is so arbitrary and ad hoc? And there is evidence that the accident is not quite frozen... The idea that the genetic code is evolving under pressure to ameliorate errors -- or indeed that it is evolving at all -- has not won universal assent. Some cogent objections were set forth as early as 1967 by Carl R. Woese of the University of Illinois at Urbana-Champaign. Among other points, he noted that if a trait is actively evolving, you would expect to see some variation. In particular he called attention to the various "extremophiles" that live at high temperature, high salt concentration, and so on. These organisms tend to have unusual proteins and unusual nucleic acids, but they all have the standard genetic code.

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I'm freezing my accident off.

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