Exaptation is a concept in evolutionary biology that refers to the process by which a feature or trait that originally evolved for one purpose is later co-opted for a different purpose.

In other words, exaptation occurs when a biological structure or behavior that evolved to serve one function becomes useful for a completely different function, often due to changes in the organism’s environment or behavior.

Exaptation can occur in various forms and across different levels of biological organization. For example, feathers, which originally evolved for insulation and display purposes, were exapted for flight in birds. The jaws of reptiles, which originally evolved for eating, were exapted for hearing in mammals. Similarly, the webbing on the feet of ducks, which originally evolved for swimming, was exapted for walking on land.

Exaptation is an important concept in evolutionary biology because it illustrates the role of chance and contingency in the evolutionary process, and highlights the potential for existing structures and behaviors to be repurposed for new uses.