The Coolidge effect is a biological phenomenon seen in animals, whereby males exhibit renewed sexual interest whenever a new female is introduced to have sex with, even after cessation of sex with prior but still available sexual partners. To a lesser extent, the effect is also seen among females with regard to their mates.
The Coolidge effect can be attributed to an increase in sexual responsiveness, and a shortening of the sexual refractory period. The evolutionary benefit to this phenomenon is that a male can fertilize multiple females. The male may be reinvigorated repeatedly for successful insemination of multiple females. This type of mating system can be referred to as polygyny, where one male has multiple female mates, but each female only mates with one or a few male mates.