A fit mouse is a hoppy mouse: jumping behavior in 15-day-old Mus musculus.

An analysis of a juvenile hopping response from an 8 X 8 diallel cross is used to demonstrate the experimental genetic approach for testing presumed adaptive fitness of behaviors in developing organisms. In accordance with predictions, the explosive jumping behavior exhibited by 15-day mice is characterized by a pattern of genetic dominance toward high expression of the trait. Wild mice show even more vigorous responses, indicating that selection pressures maintaining high responding have been relaxed during domestication. These data suggest some applications and limitations of genetic methods for the study of behavioral evolution as related to development.