Although the explanatory value of the Darwinian theory of natural selection is, as we have now seen, incalculably great, it nevertheless does not meet those phenomena of organic nature which perhaps more than any other attract the general attention, as well as the general admiration, of mankind: I mean all that class of phenomena which go to constitute the Beautiful. Whatever value beauty as such may have, it clearly has not a life-preserving value. The gorgeous plumage of a peacock, for instance, is of no advantage to the peacock in his struggle for life, and therefore cannot be attributed to the agency of natural selection. Now this fact of beauty in organic structures is a fact of wide generality--almost as wide, indeed, as is the fact of their utility. Mr. Darwin, therefore, suggested another hypothesis whereby to render a scientific explanation of this fact. Just as by his theory of natural selection he sought to explain the major fact of utility, so did he endeavour to explain the minor fact of beauty by a theory of what he termed Sexual Selection. It is a matter of observation that the higher animals do not pair indiscriminately; but that the members of either sex prefer those individuals of the opposite sex which are to them most attractive. It is important to understand _in limine_ that nobody has ever attempted to challenge this statement. In other words, it is an unquestionable fact that among many of the higher animals there literally and habitually occurs a _sexual selection_; and this fact is not a matter of inference, but, as I have said, a matter of observation. The inference only begins where, from this observable fact, it is argued,--1st, that the sexual selection has reference to an æsthetic taste on the part of the animals themselves; and 2nd, that, supposing the selection to be determined by such a taste, the cause thus given is adequate to explain the phenomena of beauty which are presented by these animals. I will consider these two points separately.