2nd. At the present time, perhaps more than ever, those who believe in species are reproached with being orthodox: I could never myself understand why there should be this mixture of scientific discussions and dogmatic and anti-dogmatic polemics.
3rd. I shall, moreover, refuse to dispute with those who, rejecting on their own authority a whole century of work accomplished by the greatest naturalists, and by a number of men distinguished in botany and zoology, declare that it is useless to try and discover what species and race are, and laugh at those who take the trouble to do so. I say the same to those who regard species and race as more or less arbitrary groups which may be compared to the genus, family and order. It will be enough to remark that they themselves incessantly employ the word species and race, and we must not be surprised if they take one thing for the other.
4th. After what we have said, discussion is useless with those naturalists who only base the distinction of species upon external characters. They forget all the experiments made from Buffon to the two Geoffroys, from Koelreuter to M. Naudin; they forget the innumerable observations made in our orchards, gardens and stables. To refuse to abandon morphological considerations, and to neglect the data of physiology and the lessons of filiation, is clearly going further back than Ray and Tournefort, and all discussion becomes impossible.
5th. Some of our opponents allow that things are now what we think them to be. “But,” say they, “it is possible that at some other time it was different.” What answer can be given to those who base their arguments upon possibilities? Is modern science composed of possibilities?
6th. Naturalists have often been reproached with multiplying the definitions of species. From the variety of terms employed by them in expressing ideas, it has been inferred that they were not agreed as to the ideas themselves. We may easily convince ourselves of their mistake, if we give these definitions a careful reconsideration. We shall see that their several authors have only endeavoured to express with greater clearness and precision, the double idea resulting from the facts of resemblance and filiation. In reality, divergencies only begin where experiment and observation cease. It is this which caused Isidore Geoffroy, however interested he might be in discussions of this nature, to remark—“Such are Species and Races, not only for one of the schools into which naturalists are divided, but for all.”
7th. It has been asserted that the distinction of species and race rests upon a syllogistic circle; that naturalists decided à priori upon calling all those groups incapable of intercrossing, species, and all those amongst which crossing was possible, races. To appeal to the difference of the phenomena presented by the hybrids and mongrels is therefore only solving the question by the question.—This is an historical error. Naturalists came into contact with species, races and varieties, before they gave names to them. It was by experiment and observation that they learnt to distinguish them. Knowledge of facts preceded terminology.
8th. Again, it has been said, that the discussions which are always arising between naturalists as to whether a species should be preserved or regarded as a race, as to the genus, family, order, and sometimes the class in which it should be placed, betray a want of precision in general ideas.—Those who talk in this manner forget the immense number of species and races accepted and classified without discussion. They shut their eyes to all cases except those in which divergences of opinion occur. If, however, facts of this nature prove anything against a science and its fundamental data, then even mathematical theorems must be considered as wanting in precision, for there are disputes among mathematicians.
9th. I have already replied to the arguments drawn from the fertility of certain hybrids by showing to what it is reduced. Writers who insist upon this point invariably forget the lesson taught us by disordered variation and reversion without atavism. I regret being obliged to place among them Darwin, who, in his later writings, has shewn much less reserve than in his earlier publications. In the last edition of his book, he quotes what I have said of the cross between the Bombyx cynthia and the Bombyx arrindia; he speaks of the number of generations obtained, but he forgets to mention that disordered variation appeared in the second generation, and that reversion to one of the parental types was almost complete at the termination of the experiment.
X. Species is then a reality.