The ultimate rationale behind all purposeful structures and behaviour of living beings is embodied in the sequence of residues of nascent polypeptide chains the precursors of the folded proteins which in biology play the role of Maxwell's demons. In a very real sense it is at this level of organisation that the secret of life (if there is one) is to be found. If we could not only determine these sequences but also pronounce the law by which they fold, then the secret of life would bt found — the ultimate rationale discovered!