To all these _a priori_ objections there may also be added the remark of Geddes and Thomson, that if the females of insects and birds had really called into existence all the detailed patterns on the dresses of their respective males by the exercise of æsthetic selection, they would possess more discrimination than is shown in their predilection for any sort of gaudy-coloured objects, such as pebbles, slips of paper, and rags.[267] However great the psychological improbability of the supposed æsthetic selection, there is still more reason to take exception to it from an evolutionistic point of view. The female appreciation for gaudy and gorgeous dresses must necessarily, as Darwin himself remarks, in many cases give rise to a plumage, as a result of which the males become encumbered in their movements and easily discovered by their enemies.[268] Æsthetic judgment, which is in itself so incomprehensible, would thus have been developed in a continuous conflict with natural selection. This circumstance, more than anything else, makes it indispensable to look for some more utilitarian cause of the secondary sexual characters and activities than the hypothetical necessity of satisfying a sense of beauty in the female sex. By the theory that has been advanced by Wallace, and further developed by Westermarck, the nuptial dresses of the males have indeed been accounted for in a simple way.[269] Reference to the need of recognisable marks for every different species can explain the most prominent characteristics in male plumage without any appeal to an æsthetic sense. This need, together with the equally great indispensability of protective colouring, must necessarily give rise to precisely such brilliant coloured spots on a monotonous or plain surface as are so often found on the bodies of the northern birds. The gaudier coloration of the tropical species, on the other hand, appears as a result of their more brilliant surroundings. Even here protective colouring often leaves to the colour of recognition only a narrow and limited space, on which this has to develop itself with so much the greater intensity. In this way one can find a reason not only for the decorations, which are beautiful according to our standard, but also for the inharmonious and glaring colour-combinations.