Porpoises show the great diversity in nature, a diversity that adds greatly to human enjoyment.
Porpoises also exemplify the fact that development takes place in stages. For, despite their aquatic, fish-like appearance, porpoises are air-breathing mammals, apparently representing a move to aquatic environments from a terrestrial existence. All development takes time and comes in stages, such as the development of a butterfly through egg, larva, pupa, and adult. The life history of the porpoise also shows this vertical development, where their present form came on the foundation of earlier stages. Even the bones in their flippers look like the bones found in terrestrial mammals. This does not mean that they developed by chance, via natural selection, but is a statement that all development takes time, based on the foundation of earlier stages, regardless of whether it is a product of design or chance.