The pertinence of the periodic selection phenomenon to prokaryote evolution.

A quarter of a century ago, it was pointed out that evolution can act in an important conservative way, in addition to its normal progressive mode. Evolution to a fitter form via changes at one locus means that the descendants of an individual with an improved locus or set of loci will supplant the previous population and carry with them the bulk of the total genotype of that original individual in asexual populations. Inasmuch as that individual is most likely to be wild type at most other loci, neutral and even other positively selected mutations will be reduced or eliminated from the population, if they are rare at the time of the evolutionary advance. In the present paper this problem has been set up for a computer simulation. The computations show the limits within which this effect functions and the conditions under which it does not. The conclusion is that it is likely that evolution at a locus proceeds in the course of many population replacements or revolutions, mostly via the rare occasions when the revolution carries a previously infrequent mutational type into abundance.