Far from co-operating with the process of natural selection, sexual selection, as described by Mr. Darwin, produces effects disadvantageous to the species. “It is evident,” he says, “that the brilliant colours, top-knots, fine plumes, &c., of many male birds cannot have been acquired as a protection; indeed, they sometimes lead to danger.”[1488] When we consider what an important part is played by colours, as means of protection, in the whole animal kingdom, it is certainly surprising that many male animals display brilliant hues, which cannot fail to make them conspicuous to their enemies. The strong odours emitted by certain reptiles and mammals, during the pairing season, and the sounds produced by various species at the same period, have also the effect of attracting hostile animals that are searching for food. And the danger arising for the species from these secondary sexual characters is all the greater because they generally appear at the time when offspring is about to be produced. Thus, besides colours, structures, and functions, adapted in the most marvellous way to the requirements of each species, there are others highly dangerous, which, according to Mr. Darwin, depend upon an æsthetic sense, the origin of which we do not know, and which is absolutely useless. Mr. Darwin, in his many works, has shown how immense is the influence exercised by natural selection on the organic world. A disciple, therefore, naturally feels perplexed when he is told of a series of facts, which, according to the explanation given by the master, are opposed to natural selection. When the contradiction between the theories of natural and sexual selection is distinctly realized, the question arises:—Can we be sure that the secondary sexual characters are so useless as Mr. Darwin suggests? May not they also be explained by the principle of the survival of the fittest? The larger size and greater strength of the males, and the weapons of offence or defence many of them possess, may easily be so accounted for, as, among the higher animals, the males generally fight with each other for the possession of the females. The point is whether the other secondary sexual characters can be due to the same cause. * * * * *