But characters exclusively due to analogous variation would probably be of an unimportant nature, for the preservation of all functionally important characters will have been determined through natural selection, in accordance with the different habits of the species.

It might further be expected that the species of the same genus would occasionally exhibit reversions to long-lost characters.

As, however, we do not know the common ancestor of any natural group, we cannot distinguish between reversionary and analogous characters.

If, for instance, we did not know that the parent rock-pigeon was not feather-footed or turn-crowned, we could not have told, whether such characters in our domestic breeds were reversions or only analogous variations; but we might have inferred that the blue colour was a case of reversion from the number of the markings, which are correlated with this tint, and which would not probably have all appeared together from simple variation.