What do we call a physical characteristic in organisms that appears to have lost its original function through evolution?

The term used for a physical characteristic in organisms that appears to have lost its original function through the process of evolution is referred to as a vestigial structure. These structures are remnants of features that served important functions in the organism’s ancestors but are no longer essential in the species today. A classic example is the human appendix, which is a reduced version of a larger cecum that was useful in herbivorous ancestors for digesting cellulose from plant material.

This concept highlights the evolutionary process where certain traits may diminish over time as the needs of the organism change, illustrating how species adapt to their environments. While adaptive traits improve an organism's fitness in its environment, or homologous structures indicate common ancestry despite serving different functions, vestigial structures specifically represent a historical aspect of adaptation that no longer serves a primary role in current organisms. Similarly, analogous structures arise from convergent evolution and serve similar functions in different species without sharing a common ancestor. Thus, vestigial structures stand out as vital evidence of evolutionary history and change.