Let us suppose that one variety of hog had been discovered in Africa, one in Asia, one in Europe, one in Australia, another in America, as well marked as those Dr. B. describes; that these varieties had been transferred to other climates as have been Jews, gypsies, negroes, &c., and had remained for ages without change of form or color, would they be considered as distinct species or not?--can any one doubt? The rule must work both ways, or the argument falls to the ground. In fact the Dr. himself makes admissions which fully refute his whole theory. "Whilst," says he, "we are willing to allow some weight to the argument advanced by President Smyth, who endeavors to account for the varieties in man from the combined influences of three causes, 'climate, the state of society, and manner of living,' we are free to admit that it is impossible to account for the varieties in the human family from the causes which he has assigned."[202] The Dr. further admits, in the same work, that the races have been _permanent_ since the time of the old Egyptian empire, and _supposes_ that at some extremely remote time, of which we have no record, that "they were more susceptible of producing varieties than at a later period." These suppositions answer a very good purpose in theology, but do not meet the requirements of science. HYBRIDITY. Having shown the insufficiency of all the other arguments in establishing the landmarks of _species_, let us now turn to those based on _hybridity_, which seems to be the last stronghold of the unity party. On this point hang all the difficulties of M. Gobineau, and had he been posted up to date here, his doubts would all have vanished. The last twelve months have added some very important facts to those previously published, and we shall, with as little detail as possible, present the subject in its newest light. It is contended that when two animals of distinct species, or, in other words, of distinct origin, are bred together, they produce a hybrid which is _infertile_, or which at least becomes sterile in a few generations if preserved free from admixture with the parent stocks. It is assumed that unlimited prolificness is a certain test of community of origin. We, on the contrary, contend that there is no abrupt line of demarcation; that no complete laws of hybridity have yet been established; that there is a _regular gradation_ in the prolificness of the species, and that, according to the best lights we now possess, there is a continued series from perfect sterility to perfect prolificacy. The degrees may be expressed in the following language:-- 1. That in which hybrids never reproduce; in other words, where the mixed progeny begins and ends with the first cross. 2. That in which the hybrids are incapable of producing _inter se_, but multiply by union with the parent stock.