SELECTION OR MUTATION - WHICH, IF EITHER, COMES FIRST

Selection-induced mutations (SIMS) are mutations that occur as specifi c and direct responses to environmental challenges, and that occur mor e often when they are selectively advantageous than when they are sele ctively neutral. This review includes discussions of how the occurrenc e of SIMS is measured, acquisitive evolution by SIMS, some of the cont roversies surrounding SIMS and models that have been advanced to expla in the specificity of SIMS, and the requirement of a functional recA g ene product for SIMS to occur.