NOTE 20G: If it is not possible for a “mixed strategy” to evolve, involving phenotypic plasticity (see, e.g., Fig. P20.5), then a genetic polymorphism may evolve. However, that may not perfectly match the ESS: For example, heterozygotes or recombinants might be produced that do not specialize perfectly. Then, there may be selection favoring speciation. This is discussed on pages 650–654.