Homology << hoh MOL uh jee >> refers to biological traits in different organisms that evolved from similar traits in a common ancestor. Such traits include biological structures, behaviors, and physiological processes.
An example of homology is the similarity between the front limbs of such animals as birds, horses, monkeys, and whales. These limbs have the same ancestry and basic structure, even though they now serve different uses. Examples of homologous behaviors exist between birds and crocodilians (alligators and related reptiles). For instance, both animal groups build nests, lay eggs, and care for their young, as did the prehistoric creature from which birds and crocodilians evolved.
In contrast, analogous traits serve similar functions in different species, but they develop from different groups of cells in the unborn young. For example, both butterflies and birds use their wings for flying, but the basic structures of these two wing types differ considerably and lack a common origin.
