| | | |(_f_) Cross-sterility in |(_f_) Cross-sterility in | |species cannot possibly be |species is probably due to | |due to natural selection. |natural selection[8]. | [8] This, to the best of my judgement, is the fairest extract that I can give of Mr. Wallace's most recently published opinions on the points in question. [In particular as regards (_a_) see _Darwinism_ pp. 435-6.] But with regard to some of them, his expression of opinion is not always consistent, as we shall find in detail later on. Besides, I am here taking Mr. Wallace as representative of the Neo-Darwinian school, one or other prominent member of which has given emphatic expression to each of the above propositions. As it will be my endeavour in the ensuing chapters to consider the rights and the wrongs of these antithetical propositions, I may reserve further quotations from Darwin's works, which will show that the above is a correct epitome of his views as contrasted with those of Wallace and the Neo-Darwinian school of Weismann. But here, where the object is merely a statement of Darwin's theory touching the points in which it differs from those of Wallace and Weismann, it will be sufficient to set forth these points of difference in another and somewhat fuller form. So far then as we are at present concerned, the following are the matters of doctrine which have been clearly, emphatically, repeatedly, and uniformly expressed throughout the whole range of Darwin's writings. 1. That natural selection has been the main means of modification. 2. That, nevertheless, it has not been the only means; but has been supplemented or assisted by the co-operation of other causes. 3. That the most "important" of these other causes has been the inheritance of functionally-produced modifications (use-inheritance); but this only because the transmission of such modifications to progeny must always have had immediate reference to _adaptive_ ends, as distinguished from merely useless change. 4. That there are sundry other causes which lead to merely useless change--in particular, "the direct action of external conditions, and variations which seem to us in our ignorance to arise spontaneously." 5. Hence, that the "principle of utility," far from being of universal occurrence in the sphere of animate nature, is only of what may be termed highly general occurrence; and, therefore, that certain other advocates of the theory of natural selection were mistaken in representing the universality of this principle as following by way of necessary consequence from that theory.