Two Metres of Instructions

Biology · · 1 min read · By No Design Editorial

Chemistry permits the order of the letters in DNA. It does not dictate it. That gap is the whole argument, and it is not a gap in our knowledge.

The short version

  • Chemistry permits the order of the letters in DNA. It does not dictate it. That indifference is not a gap in our knowledge; it is what lets the molecule mean anything.
  • Copying runs at roughly one uncorrected error in ten billion letters, through three stacked layers of selection, proofreading and repair.
  • Error correction only makes sense against a standard. Chemistry has no opinion about which base ought to be there.

The human genome runs past three billion letters. Read them aloud at one per second, without pause, and you would not finish for about ninety-five years. Stretched out, the DNA in a single cell would reach about two metres, and it folds into a nucleus a few thousandths of a millimetre across while staying readable, copyable and repairable.

The packing is impressive. The argument is elsewhere, and it is easy to miss.

The bond joining each base to the sugar-phosphate backbone has effectively the same energy regardless of which base it is. Chemistry is indifferent to the order. That indifference is not a gap in our knowledge waiting to be filled in; it is the reason DNA can carry information at all. A medium that chemistry forced into one arrangement could not spell anything, in the same way that a magnet forcing iron filings into a fixed pattern cannot write a sentence. Michael Polanyi made this point in 1968 and it has not been answered since.

There is a second argument that usually gets run together with the first, and it is the less familiar one. DNA replication is proofread in a cascade: the polymerase selects correctly to about one error in a hundred thousand, proofreading catches most of what slips through, and mismatch repair catches most of the rest, ending near one error in ten billion.

Sit with what error correction requires. A system can only correct a mistake if there is a standard defining what counts as a mistake. Chemistry has no opinion about which base 'should' be there. Something has to specify the correct state before an error can be recognised as an error.

From Chapter 5: Signs in the Small.

Tags: DNA, Information, Error Correction, Quran