Homology

The living organisms placed in a particular group all have many fundamental similarities, in their structure. It is not always easy to recognize these basic similarities. At first sight, the flipper of a whale is used for swimming, the wing of a bat for flight and the arm of a man for gaping, do not seem to have much in common, yet if one examines their internal structure--- the bones and muscles--- it can be seen that the three are very much like. The flipper, wing, and arm are all built on the same pattern. During the course of evolution, each has been modified from the basic pattern to serve a particular,and usually highly specialized function, due to its adaptation to different environment/habitat.