A male rat is placed in a box with several other female rats.
Following its natural instincts, the male begins to mate with the different females repeatedly until sexual exhaustion means it can no longer continue. Despite renewed attempts at intimacy from the female rats, the male cannot respond until a new female is placed into the box.
The presence of this new mate immediately sparks the male back into life and it begins to mate again, solely with the novel female, until it tires once more.
Another new female is then introduced and the process repeats.
This is an experiment by Frank A. Beach, an American ethologist. The experiment later became known as the Coolidge Effect.
The theory that it is not the act of sex that dominates the male rat’s arousal but variety in its sexual experience. It is a biological and psychological phenomenon that has occurred in the evolution of mammalian species including humans.
In recent years the Coolidge Effect been re-appropriated to explain human behaviour in relation to pornography, which you can find out more about in our blog: “The Great Porn Experiment”