There is only one other remark to be made in this connexion. Mr. Syme chooses two cases as illustrations of the supposed difficulty. These are sufficiently diverse--viz. Foraminifera and Man. Touching the former, there is nothing that need be added to the general answer just given. But with regard to the latter it must be observed that the dominion of natural selection as between different races of mankind is greatly restricted by the presence of rationality. Competition in the human species is more concerned with wits and ideas than with nails and teeth; and therefore the "struggle" between man and man is not so much for actual _being_, as for _well-being_. Consequently, in regard to the present objection, the human species furnishes the worst example that could have been chosen. * * * * * Hitherto I have been considering objections which arise from misapprehensions of Darwin's theory. I will now go on to consider a logically sound objection, which nevertheless is equally futile, because, although it does not depend on any misapprehension of the theory, it is not itself supported by fact. The objection is the same as that which we have already considered in relation to the general theory of descent--namely, that similar organs or structures are to be met with in widely different branches of the tree of life. Now this would be an objection fatal to the theory of natural selection, supposing these organs or structures in the cases compared are not merely analogous, but also homologous. For it would be incredible that in two totally different lines of descent one and the same structure should have been built up independently by two parallel series of variations, and that in these two lines of descent it should always and independently have ministered to the same function. On the other hand, there would be nothing against the theory of natural selection in the fact that two structures, _not_ homologous, should come by independent variation in two different lines of descent to be adapted to perform the same function. For it belongs to the very essence of the theory of natural selection that a useful function should be secured by favourable variations of whatever structural material may happen to be presented by different organic types. Flying, for instance, is a very useful function, and it has been developed independently in at least four different lines of descent--namely, the insects, reptiles, birds, and mammals. Now if in all, or indeed in any, of these four cases the wings had been developed on the same anatomical pattern, so as not only to present the analogical resemblance which it is necessary that they should present in order to discharge their common function of flying, but likewise an homologous or structural resemblance, showing that they had been formed on the same anatomical "plan,"--if such has been the case, I say, the theory of natural selection would certainly be destroyed.