The maternal pheromone of the rat as an innate stimulus for pre-weanling young.

We undertook to determine whether previous exposure in the nest is necessary to establish the attractiveness of the maternal pheromone or whether that attractiveness is innately based. In Experiment I we showed that the pheromone is a prepotent stimulus insofar as it is approached in preference to a different but equally familiar odor. Experiment 2 demonstrated that when pups are denied previous exposure to the pheromone they nonetheless approach the pheromone preferentially in a choice test involving a pheromone-emitting and a non-pheromone-emitting female. And finally, in Experiment 3, we again used pups that had been isolated from the pheromone. Here, however, the choice was between a pheromone-emitting female and a female which, while non-pheromone-emitting, carried a thoroughly familiar nest odor. The pups decisively chose the pheromone-emitting female. We conclude that pheromonal attractiveness is innately based and suggest that the pheromone itself may have been selected as a signal during the course of evolution.