Concept:Similar characteristics in unrelated species that arise due to similar environmental demands are called analogous structures.Explanation:The flippers of a whale and the fins of a fish perform the same function, which is swimming.Whales are mammals, while fish are not closely related to them.Because their body parts look alike but have different evolutionary origins, they are analogous structures.Such features develop through convergent evolution, where different organisms independently adapt in similar ways.Answer:D. convergent evolution.