The intention of this work is to eliminate the need for a synchronous generation scheme in the (/spl mu//sup /spl plusmn///spl lambda/) evolution strategy. It is motivated by the need for a more practical implementation of selection strategies on parallel machine architectures. This strategy is known as continuous or steady state selection. Continuous selection is known to reduce significantly the number of function evaluations needed to reach an optimum in evolutionary search. Evolution strategy theory is used to illustrate when continuous selection is more efficient than generational selection. The authors also consider how this gain in efficiency may influence the overall effectiveness of the evolution strategy. The implementation of continuous selection becomes problematic for algorithms using explicitly encoded self-adaptive strategy parameters. Self-adaption is therefore given special consideration. The discussion leads a new evolution strategy version. © 2002 IEEE.