Takeover mechanisms and early biochemical evolution.

It is common feature of comparatively recent evolution that a structure adapted to one function turns out also to have another function, or another way of performing an existing one. It is proposed that while our central biochemical machinery was actively evolving there were such discoveries and takeovers that provided routes to radically new disigns. The recognition and control techniques of protein would seem to be replacements for earlier approaches to similar functions. Polynucleotides may have been more widely used here in a pre-protein era. But even nucleic acid is seen as the outcome of a takeover, from an earlier quite different genetic material with properties more appropriate to primitive conditions and to primitive techniques of molecular control.