Convergent evolution is based on two genetically dissimilar creatures evolving similar traits or methods of filling an ecological niche. There are other cases of this such as dolphin fins and fish fins.

Bat Wing

Looking at the internal structure of the bat one can see that the wing is made up of the arm and the hand in which the fingers have become webbed together.

Bird Wing Bones

The Bird wing, on the other hand, has a very different bone structure. The webbing as in the bat is not present and a great deal of the lift needed to fly is provided by feathers.

While one might be tempted by the fact that both birds and bats have wings to classify them in a group together, scientists today have a different method of classifying these organisms.

Upon closer examination it is apparent the internal physiology of the bat is most similar to humans in that many of the organs, such as alveolar lungs, are constructed in the same manner. Bats also bear live young, have hair and are fed milk at birth. This means that even though the chicken and the bat both fly and humans do not, the bat is thought of as more closely related to the human than the chicken.

One reason that supports the classification of superficially dissimilar organisms is the study of embryology. Embryology can prove that genetic relation because as the embryo goes through early development it starts out the most similar to its closest relatives. The embryo chicken and the embryo bat are very different. They have very different appearances and stages of development. The human embryo on the other hand shares many of the bat embryo's traits further showing how the bat is more closely related to humans.