Which word is defined as a reduced form of a functional structure in 1 organism that shows up as fully functional in another?

• A. Analogous structures
• B. Vestigial structures
• C. Homologous structures
• D. Adaptive structures

Answer: (B)

Vestigial structures are remnants of a feature that was functional in an ancestor but has become reduced or nonfunctional in a current organism, while that same feature can remain fully functional in another related species. This shows how evolution can modify or lose parts that are no longer needed in a particular environment, even as they stay functional in other lineages. A classic example is the human tailbone, a reduced form of a tail that was functional in our ancestors, whereas in other animals the tail vertebrae remain fully functional. This idea contrasts with structures that are similar because of convergent evolution (analogous) or because they come from a common ancestor and may be similarly or differently shaped (homologous).