Perhaps the most straightforward method for detecting gene-environment interaction is found in animal experimentation: Different genetic strains of animals can be subjected to different environments to directly test for gene-environment interaction. The key advantage of animal studies is that environmental exposure can be made random to genotype, eliminating gene-environment correlation and associated problems with interpretation. The most widely cited example of this line of research is Cooper and Zubek’s 1958 experiment, in which rats were selectively bred to perform differently in a maze-running experiment (Cooper & Zubek 1958). Under standard environmental conditions, one group of rats consistently performed with few errors (“maze bright”), while a second group committed many errors (“maze dull”). These selectively bred rats were then exposed to various environmental conditions: an enriched condition, in which rats were reared in brightly colored cages with many moveable objects, or a restricted condition, in which there were no colors or toys. The enriched condition had no effect on the maze bright rats, although it substantially improved the performance of the maze dull rats, such that there was no difference between
