Figure 4.4 Environments, phenotypes, and fitness. Different environments cause phenotypes to experience different amounts of fitness. (a) Phenotypic plasticity evolves because a phenotype has high fitness in one environment and low fitness in another environment. (b) Given this trade-off, nonplastic genotypes have high fitness in one environment but low fitness in other environments. In contrast, a plastic genotype can have high fitness in both environments. (c) If we consider the average fitness across both environments, we see that the plastic genotype experiences higher average fitness than either of the two nonplastic genotypes.