Which term describes an organ that no longer serves a purpose after the evolution of a species?

The term that describes an organ that no longer serves a purpose after the evolution of a species is known as a vestigial organ. Vestigial structures are remnants of features that were once functional in an ancestor but have lost their original purpose due to changes in the species' environment or lifestyle over time. An example of a vestigial organ in humans is the appendix, which is considered to have had a digestive function in ancestral species but is now largely reduced and not essential for survival.

Understanding this concept is crucial in the study of evolution and biology, as it provides insight into how species adapt and change over generations. While functional organs serve a clear purpose in an organism's physiological processes, vestigial organs represent an evolutionary history and highlight the dynamism of biological functions. The other terms do not accurately capture this specific characteristic of evolutionary development.