[121] Allusion may here again be made to the case of the niata cattle. For here is a case where a very extreme variety is certainly not unstable, nor produced in varying proportions from the parent form. Moreover, as we have seen in the preceding chapter, this almost monstrous variety most probably originated as an individual sport—being afterwards maintained and multiplied for a time by artificial selection. Now, whether or not this was the case, we can very well see that it may have been. Hence it will serve to illustrate another possibility touching the origin and maintenance of useless specific characters. For what is to prevent an individual congenital variation of any kind (provided it be not harmful) from perpetuating itself as a "varietal," and eventually, should offspring become sufficiently numerous, a "specific character"? There is nothing to prevent this, save panmixia, or the presence of free intercrossing. But, as we shall see in the next division of this treatise, there are in nature many forms of isolation. Hence, as often as a small number of individuals may have experienced isolation in any of its forms, opportunity for perpetuation will have been given to any congenital variations which may happen to arise. Should any of these be pronounced variations, it would afterwards be ranked as a specific character. I do not myself think that this is the way in which indifferent specific characters usually originate. On the contrary, I believe that their origin is most frequently due to the influence of isolation on the average characters of the whole population, as briefly stated in the text. But here it seems worth while to notice this possibility of their occasionally arising as merely individual variations, afterwards perpetuated by any of the numerous isolating conditions which occur in nature. For, if this can be the case with a varietal form so extreme as to border on the monstrous, much more can it be so with such minute differences as frequently go to constitute specific distinctions. It is the business of species-makers to search out such distinctions, no matter how trivial, and to record them as "specific characters." Consequently, wherever in nature a congenital variation happens to arise, and to be perpetuated by the force of heredity alone under any of the numerous forms of isolation which occur in nature, there will be a case analogous to that of the niata cattle.
[122] It is almost needless to say that by a definition as "logical" is meant one which, while including all the differentiae of the thing defined, excludes any qualities which that thing may share in common with any other thing. But by definitions as "logically possible" I mean the number of separate definitions which admit of being correctly given of the same thing from different points of view. Thus, for instance, in the present case, since the above has been in type the late M. Quatrefages' posthumous work on Darwin et ses Précurseurs Français has been published, and gives a long list of definitions of the term "species" which from time to time have been enunciated by as many naturalists of the highest standing as such (pp. 186-187). But while none of these twenty or more definitions is logical in the sense just defined, they all present one or other of the differentiae given by those in the text.
[123] Darwinism, p. 167.
[124] Nature, Dec. 12, 1889, p. 129.
[125] Darwinism, p. 77.
[126] Darwinism, p. 77.
[127] Pascoe, The Darwinian Theory of the Origin of Species, 1891, pp. 31-33, and 46.
[128] Neuer Beitrag zum geologischen Beweis der Darwinischen Theorie, 1873.
[129] The Doctrine of Descent and Darwinism, Eng. Trans. p. 102.
[130] Origin of Species, p. 175.