So much for what Weismann has said touching this matter. But the matter has also been dealt with both by Darwin and by Wallace. Darwin very properly distinguishes between the fallacy that "with animals such as the giraffe, of which the whole structure is admirably co-ordinated for certain purposes, it has been supposed that all the parts must have been simultaneously modified[39]," and the sound argument that the co-ordination itself cannot have been due to natural selection alone. This important distinction may be rendered more clear as follows. [39] _Variation_, &c., vol. ii. p. 206. The facts of artificial selection prove that immense modifications of structure may be caused by a cumulative blending in the same individuals of characters which were originally distributed among different individuals. Now, in the parallel case of natural selection the characters thus blended will usually--if not invariably--be of an adaptive kind; and their eventual blending together in the same individuals will be due to free intercrossing of the most fit. But this _blending of adaptations_ is quite a different matter from the _occurrence of co-ordination_. For it belongs to the essence of co-ordination that each of the co-ordinated parts should be destitute of adaptive value _per se_: the adaptation only begins to arise if all the parts in question occur associated together in the same individuals _from the very first_. In this case it is obvious that the analogy of artificial selection can be of no avail in explaining the facts, since the difficulty presented has nothing to do with the blending in single individuals of adaptations previously distributed among different individuals; it has to do with the simultaneous appearance in single individuals of a co-adaptation of parts, none of which could ever have been of any adaptive value had it been previously distributed among different individuals. Consequently, where Darwin comes to consider this particular case (or the case of co-adaptation as distinguished from the blending of adaptations), he freely invokes the aid of the Lamarckian principles[40]. [40] E. g. _Origin of Species_, p. 178.