Figure 5. The selective sieve. The five colored plates represent various hypothetical environmental forces (such as temperature, chlorophyll density, etc), that are highly variable among years. This represent the different selection pressures encountered by the Pacific Ocean Perch during initial pelagic life stage. Each years’ cohort therefore contains the alleles that were selected for during their first year. Populations of long-lived adults representing multiple cohorts maintain genetic diversity as a result of this temporal variation in selection.