In principle evolution ought to be a runaway process. The constant scrutiny of selection and the pressure of adaptational advantage, be it ever so slight, should in principle lead to the emergence of a complex biosphere during a geological period far less than it actually took. One famous example that drives this point home is an estimate of the time needed for a complex camera-eye to evolve from a simple eye-spot (see Nilsson & Pelger, 1994). On the basis of rather modest assumptions these workers show that the process should take less than half-a-million years. What applies to complex...

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