When our interest in sex starts to wane, exposure to a new or novel partner has a way of bringing it back. This phenomenon--formally dubbed the Coolidge Effect--got its name from a popular anecdote about a visit that U.S. President Calvin Coolidge and his wife supposedly made to a chicken farm. The story goes something like this:

“Mrs. Coolidge, observing the vigor with which one particularly prominent rooster covered hen after hen, asked the guide to make certain that the President took note of the rooster’s behavior. When President Coolidge got to the hen yard, the rooster was pointed out and his exploits recounted by the guide, who added that Mrs. Coolidge had requested that the President be made aware of the rooster’s prowess. The president reflected for a moment and replied, ‘Tell Mrs. Coolidge that there is more than one hen.’” [1]

The Coolidge Effect has been documented in several animal species. For instance, research has found that when a male rat is placed inside a cage with several female rats that are in heat, he will mate with all of them until he appears exhausted. However, if a new female is then introduced to the cage, males often experience an immediately renewed interest in sex and begin mating with her [2].

The Coolidge Effect has been documented in humans as well. For instance, in one study, male participants were either exposed to constant or varied sexual stimuli while their level of sexual arousal was measured by a device that records changes in penile circumference [3]. The men who were repeatedly shown the same stimuli showed less arousal over time (in other words, they demonstrated habituation); by contrast, men who were exposed to varied stimuli maintained higher levels of arousal.

Another study found that, after watching porn clips featuring the same actress over a period of several days, exposure to porn featuring a new actress was linked not only to faster ejaculation, but also the release of more active sperm [4]. This suggest that the Coolidge Effect may have an evolutionarily explanation behind it in that it might potentially increase men's odds of reproductive success with new partners.

The Coolidge Effect has also been documented in females, although the pattern tends to be somewhat less pronounced. For instance, research on female hamsters has found that after mating with one male hamster until exhaustion, they demonstrate renewed interest in sex when a new male is introduced to the cage [5]. Also, research on women has found that, just like men, they show some degree of habituation in response to repeated presentations of the same erotic stimulus [6]. What this tells us is that the Coolidge Effect isn’t a uniquely male phenomenon by any stretch of the imagination.