Pigeons’ Wings
Concerning pigeons’ wings Darwin says: “As fancy pigeons are generally confined in aviaries of moderate size, and as even when not confined they do not search for their own food, they must during many generations have used their wings incomparably less than the wild rock-pigeon... but when we turn to the wings we find what at first appears a wholly different and unexpected result.”27 This unexpected increase in the spread of the wings from tip to tip is due to the feathers, which have lengthened in spite of disuse. Excluding the feathers, the wings were shorter in seventeen instances, and longer in eight. But as artificial selection has lengthened the wings in some instances, why may it not have shortened them in others? Wings with shortened bones would fold up more neatly than the long wings of the Carrier pigeon for instance, and so might unconsciously be favoured by fanciers. The selection of elegant birds with longer necks or bodies would cause a relative reduction in the wings—as with the Pouter, where the wings have been greatly lengthened but not so much as the body.28 Slender bodies, too, and the lessened divergence of the furculum,29 would slightly diminish the spread of the wings, and so would affect the measurements taken. As the wing-bones, moreover, are to some extent correlated with the beak and the feet, the artificial selection of shortened beaks might tend to shorten the wing as well as the feet. Under these circumstances how can we be sure of the actual efficacy of use-inheritance? Surely selection is as fully competent to effect slight changes in the direction of use-inheritance as it undoubtedly is to effect great changes in direct opposition to that alleged factor of evolution.