In some animals, the same structure developed along different directions due to adaptations to different needs This is divergent evolution and is called homology. Homology indicates common ancestry. For example, vertebrate hearts or brains. In plants also, the thorn and tendrils of Bougainvillea and Cucurbitarepresent homology. Wings of butterfly and of birds look alike. They are not anatomically similar structures though they perform similar functions. Analogy results from convergent evolution in which different structures evolve for the same function and hence have similarity. Sweet potato (root modification) and potato (stem modification) is another example for analogy.