Tryon's Rat Experiment

Experiment set-up

Prior to Robert Tryon’s study of Selective breeding in rats, concluded in 1942, many psychologists believed that environmental, rather than genetic, differences produced individual behavioral variations. Tryon sought to demonstrate that genetic traits often did, in fact, contribute to behavior. To do so, Tryon created an experiment that tested the proficiency of successive generations of rats in completing a maze. He initiated the experiment by exposing a genetically diverse group of rats to the maze, labeling those who made the fewest errors “bright”, and those with the most errors “dull”. Tryon then mated the “bright” males with “bright” females, and “dull” males with “dull” females. After their children matured, Tryon repeated the maze test with them, and again separated the “bright” and the “dull”, again breeding “bright” with “bright” and “dull” with “dull”. Tryon continued this process for seven generations, creating two distinct breeds of “bright” and “dull” rats. In order to demonstrate that behavior had little effect on the genetically selectively bred rats, and lessen the chance of error when making his conclusions, Tryon cross-fostered the rats—that is, he had a “dull” mother raise “bright” children, and vice versa. The independent variables in his experiment were the parental pairings, the choice of environment and parents for upbringing, and number of rats put through the maze. The dependent variable was the number of errors made by the rats in 19 trials of the maze.