An important evidence in favour of organic evolution is the occurrence of homologous and vestigial organs. Homologous organs have a common origin and are built on the same fundamental pattern, but they perform different functions and have different appearances. Vestigial organs in animals have no function now, but they had important functions in ancestors. Analogous organs are quite different in fundamental structure and embryonic origin but perform the same function. The study of analogous organs illustrates the occurrence of convergent evolution.