Answer:
When comparing homologous structures, we are comparing the anatomy of one part of an organism to another and finding it to be structurally similar but functionally may be different. Let’s compare a couple of tetrapods, specifically a human arm and a cat arm.
Both the human arm and the cat arm have a single bone in the upper arm, which we call the humerus, followed by two bones in the forearm–the radius on the more medial side and the ulna on the more lateral side. Both arms also have a common wrist structure followed by a grouping of metacarpals and phalanges. All of these structures are similar; however, these structures do not have the same function. Cats are quadrupeds that use their arms for walking and maybe a little climbing and hunting for outdoor cats. Humans, on the other hand, use their arms and hands for gross motor movement like grabbing, hugging, and lifting, as well as fine motor movement like using tools or even communicating.
A whale flipper and a bat wing are also homologous structures in the same sense as a human arm and cat arm with a humerus, radius and ulna, and so on. But the whale’s “arm” is actually a flipper that it uses to swim while the bat uses its wing to fly.
