In ESs selection is completely deterministic. The best individuals from the population of offspring or from the combination of the previous parents and their offspring are chosen as parents for the next generation. The former scheme is known as -selection, the latter as -selection.
Though -selection is elitist, -selection is, in general, preferred, because it is better able to adapt to changing environments (a common feature of the parameter optimization problems for which ESs were originally developed). Schwefel  recommends a ratio of : of 1:7.