Often a type of organ or body structure is the only physically feasible means of accomplishing a given task, so it should be unsurprising if, like eyes or wings, that type of organ or body structure evolves at different times in a number of completely unrelated species. After all, whatever the difference of heritage and habitat, as organisms animals have fundamentally similar needs and so __.
The statement 'will in many instances evolve similar adaptations enabling them to satisfy these needs' most logically completes the last sentence of the passage.