The subject of phenotypic plasticity is a relatively untouched area of biological study. The subject is comprised of a great deal of variables when it come to evolution that make defining the heritability of plasticity difficult. Phenotypic plasticity is the ability for a genotype to produce several phenotypes when the organism is subjected to different environmental factors. One subcategory of phenotypic plasticity involves genes expressing behavioral traits.
Behavioral traits are attributed to a combination of the organisms genes and its environment. Plasticity of a behavioral trait reveals different reaction norms, or a pattern of phenotypic expression, for the organism when exposed to different environmental stimuli. The environment causes either an up or down regulation of behavioral response as cues from the environment change. Individuals in a population can differ in the degree and directionality in which their behavior presents from the same stimuli. Even neighboring organisms of the same species may differ in both aspects. This phenomenon is able to occur because, just as genes can mutate and evolve, so can plasticity. The variation in degree and directionality is also due to the fact plasticiy evolves independenly from the gene which expresses the trait it effects.