Gene-environment interaction is a term used to describe any phenotypic effects that are due to interactions between the environment and genes. Naive nature versus nurture debates assume that variation in a given trait is primarily due to either genes, or the individual's experiences. The current scientific view is that neither genetics nor environment are solely responsible for producing individual variation, and that virtually all traits show gene-environment interaction. The specific pattern that relates the average expression of trait across a range of environments is known as a genotype's norm of reaction.
A classic example of gene-environment interaction is Tryon's selection experiment on maze-running ability in rats.() artificial Tryon produced a remarkable difference in maze running ability in two selected lines after seven generations of selecting "bright" and "dull" lines by breeding the best and worst maze running rats with others of similar abilities. The difference between these lines was clearly genetic since offspring of the two lines, raised under identical typical lab conditions, performed too differently. This difference disappeared in a single generation, if those rats were raised in an enriched environment () with more objects to explore and more social interaction. This result shows that maze running ability is the product of a gene-by-environment interaction, the genetic effect is only seen under some environmental conditions.