When this option is checked, the Pareto frontier multi-objective optimization technique is applied to the entire set of simulated progenies, and only those simulated progenies that have the scoring values of traits lying at the optimized frontier (as specified by entries in the List of optimization sense for progeny selection field) are selected and crossed (backcrossed or selfed) to produce the next breeding generation.
Check the Select best simulated progenies to cross check box.