When you think about it, structure is often but perhaps not always necessary for function of a certain ability in any organism.
Wings for example give organisms the ability to fly, so the structure of their wings enables them to fly. Without wings, they wouldn't be able to fly (excluding free fall or using technology).
Also important is too understand that we adapt through changing our abilities - function ever so slightly from generaton to generation to adapt to a certain environment where we live, this can then change structure accordingly to ensure proper function for the new ability.
