What type of structures have lost their original function over time?

Vestigial structures are those that have diminished in size or functionality over the course of evolution and no longer serve the purpose they once did in ancestral species. These structures are evidence of evolutionary processes, reflecting a history of adaptation and change. Classic examples include the human appendix, which is a remnant of a larger cecum that was once used for digesting cellulose in herbivorous ancestors, and the pelvic bones in whales, which are remnants from their land-dwelling ancestors.

The presence of vestigial structures supports the theory of evolution, as they indicate that organisms have adapted to their environments over time, leading to changes in the utility of certain anatomical features. This concept contrasts with functional structures, which still serve a clear purpose within the organism.