old one. Of what use can this thin projection, an inch or so beyond the serviceable fan of the tail, be to the bird? Seeing how well every other bird does without it, can we suppose it to be of any service? Its beauty, however—which one misses dreadfully in the young flying bird—is apparent to any one, and it goes hand in hand with an ascending scale of beauty in colour. All this seems to me to point strongly towards sexual selection as the agency by which these changes have been, and are being, effected;[1] since I am, personally, a believer in the reality of that power, having never heard or read anything against it, so convincing to my mind as what Darwin said for it, nor seen anything that has appeared to me to be inconsistent either with his facts or his arguments.
No doubt if the varied coloration of the Arctic skua is really to be explained in this way, the lighter coloured forms, especially the extreme one, in which the whole under surface is cream, ought to be on the increase, whilst the dark ones should ultimately die out or remain, perhaps, as a separate species, the intermediate tintings having disappeared. It is very difficult to form an idea of the relative number of individuals constituting any one form, because one unconsciously compares such form with a great many others instead of with each separately; but, whereas I remember various repetitions of the extreme light or
- ↑ It is a strong enforcement, I think, of this view, that in another variable species of skua—Stercorarius pomatorhinus—the same two feathers give the bird "the grotesque appearance of having a disk attached to its tail."
