Structures that were once functional in the past but no longer serve a purpose due to evolutionary adaptations and physiological changes are referred to as:

Explanation

Vestigial structures are those that have lost their original function through evolution. These structures are present in organisms because they do not impose any disadvantage, and therefore, there is no selective pressure to eliminate them. An example is the human appendix, which is a remnant of a larger cecum that was used for digesting cellulose in the diet of our herbivorous ancestors. The other options are incorrect: analogous structures result from convergent evolution and perform similar functions without a common ancestry, and homologous structures arise from a common ancestor but may have different functions. Therefore, the correct answer is vestigial structures.