Here, then, we have unquestionable evidence of a whole congeries of very distinctive characters, so unlike anything that occurs in any other cattle, that, had they been found in a state of nature, they would have been regarded as a distinct species. And the highly peculiar characters which they present conform to all "the most essential features of specific characters," as these are stated by Mr. Wallace in his objection to the case of the pig's appendages. That is to say, "they _are_ symmetrical, they _are_ inherited, and they _are_ constant." In point of fact, they are _always_ "constant," both as to occurrence and symmetry, while they are so completely "inherited" that not only does "a niata bull and cow _invariably_ produce niata calves"; but even when crossed with other cattle the result is a _hybrid_, "with the niata character _strongly_ displayed." Hence, if we were to follow Mr. Wallace's criteria of specific characters, which show that the pig's appendages "cannot be classed with specific characters" (or with anything of the nature of specific characters), it would follow that the niata peculiarities _can_ be so classed. This, therefore, is a case where he will find all the reasons which in other cases he takes to justify him in falling back upon the argument from ignorance. The cattle are half wild, he may urge; and so the three-fold constancy of their peculiar characters may very well be due, either directly or indirectly, to natural selection--i.e. they may either be of some hidden use themselves, or correlated with some other modifications that are of use: it is, he may say, as in such cases he often does say, for us to disprove both these possibilities. Well, here we have one of those rare cases where historical information, or other accidents, admit of our discharging this burden of proving a negative. Darwin's further description shows that this customary refuge in the argument from ignorance is most effectually closed. For-- "When the pasture is tolerably long, these cattle feed as well as common cattle with their tongue and palate; but during the great droughts, when so many animals perish on the Pampas, the niata breed lies under a great disadvantage, and would, if not attended to, become extinct; for the common cattle, like horses, are able to keep alive by browsing with their lips on the twigs of trees and on reeds; this the niatas cannot so well do, as their lips do not join, and hence they are found to perish before the common cattle. This strikes me as a good illustration of how little we are able to judge from the ordinary habits of an animal, on what circumstances, occurring only at long intervals of time, its rarity or extinction may depend. It shows us, also, how natural selection would have determined the rejection of the niata modification, had it arisen in a state of nature[105]." [105] Darwin, _Variation_, &c. vol. i. p. 94.