Exaptation

The physical features of an animal's body usually serve a specific purpose—they function to increase the animal's chances of survival. But, over time, in response to a particular challenge in its environment, an animal species will sometimes use one of its existing features for a new purpose. This is known as exaptation. By finding another use for one of its physical features, exaptation allows animals to respond to additional challenges in their environment. The animal may continue to use the physical feature for its older purpose, while also using it for the new purpose.