 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.