Many readers, and some writers of books on organic evolution, seem quite unaware that Darwin established two modes of selection, both alike "natural" but acting in different ways and producing somewhat different results. He termed the second mode "sexual selection," and in his _Origin of Species_ he briefly describes it as consisting in the fighting of males for the possession of females, which undoubtedly occurs in numbers of the higher vertebrates and also in insects. But he also includes under sexual selection another mode of rivalry by the display of the special male ornaments of many birds, and the choice of the more ornamental by the females. To this latter phase he devotes nearly half his volume on _The Descent of Man, and on Selection in Relation to Sex_. Selection by the fighting of males has led to the development of the stag's antlers, the boar's tusks, and the lion's mane serving as a shield. These combats rarely lead to the death of the vanquished, but to a larger number of offspring for the victor; and this leads to the improvement of the race by keeping up its strength, vigour, and fighting power. The other form of selection, by the display of ornaments by male birds and the supposed continuous development of those ornaments by the appreciative choice of the females, I believe to be imaginary. I have discussed this subject in many of my books, and my views are now generally adopted by evolutionists. The fact that the colours of male insects, especially butterflies, are almost exactly parallel to those of birds, first led me to this conclusion, because we can hardly suppose insects to be endowed with any æsthetic sense, even if they really _see_ colour at all, which, in my last book, I have given strong reasons for doubting. But in the human race the conditions are altogether different; for while, as I have shown in Chapter XIV., the kind of natural selection which through all the ages had moulded the infinitely varied animal forms into harmony with their environment, ceased to act upon man's body and only for a limited time upon his lower mental faculties, sexual selection tended to act if at all prejudicially, through polygamy, prostitution, and slavery, though it possesses the potentiality of acting in the future so as to ensure Intellectual and Moral Progress, and thus elevate the race to whatever degree of civilisation and well-being it is capable of reaching in earth-life. _Eugenics, or Race Improvement through Marriage_