Could we "let by-gones be by-gones," and, beginning now, go on improving and diversifying for the future by natural selection,--could we even take up the theory at the introduction of the actually existing species, we should be well content, and so perhaps would most naturalists be. It is by no means difficult to believe that varieties are incipient or possible species, when we see what trouble naturalists, especially botanists, have to distinguish between them,--one regarding as a true species what another regards as a variety; when the progress of knowledge increases, rather than diminishes, the number of doubtful instances; and when there is less agreement than ever among naturalists as to what the basis is in Nature upon which our idea of species reposes, or how the word is practically to be defined. Indeed, when we consider the endless disputes of naturalists and ethnologists over the human races, as to whether they belong to one species or to more, and if to more, whether to three, or five, or fifty, we can hardly help fancying that both may be right,--or rather, that the uni-humanitarians would have been right several thousand years ago, and the multi-humanitarians will be a few thousand years later; while at present the safe thing to say is, that, probably, there is some truth on both sides. "Natural selection," Darwin remarks, "leads to divergence of character; for more living brings can be supported on the same area the more they diverge in structure, habits, and constitution," (a principle which, by the way, is paralleled and illustrated by the diversification of human labor,) and also leads to much extinction of intermediate or unimproved forms. Now, though this divergence may "steadily tend to increase," yet this is evidently a slow process in Nature, and liable to much counteraction wherever man does not interpose, and so not likely to work much harm for the future. And if natural selection, with artificial to help it, will produce better animals and better men than the present, and fit them better to "the conditions of existence," why, let it work, say we, to the top of its bent. There is still room enough for improvement. Only let us hope that it always works for good: if not, the divergent lines on Darwin's diagram of transmutation made easy ominously show what small deviations from the straight path may come to in the end.