Since food and climate, and still less man's empire over them, can have but little effect upon wild animals, Buffon refers their principal varieties in great measure to their sexual habits, variations being much less frequent among animals that pair and breed slowly, than among those which do not mate and breed more freely. After running rapidly over several animals, and discussing the flexibility or inflexibility of their organizations, he declares the elephant to be the only one on which a state of domestication has produced no effect, inasmuch as "it refuses to breed under confinement, and cannot therefore transmit the badges of its servitude to its descendants."[124] Here is an example of Buffon's covert manner, in the way he maintains that descent with modification may account not only for specific but for generic differences. "But after having taken a rapid survey of the varieties which indicate to us the alterations that each species has undergone, there arises a broader and more important question, how far, namely, species themselves can change--how far there has been an older degeneration, immemorial from all antiquity, which has taken place in every family, or, if the term is preferred, _in all the genera_ under which those species are comprehended which neighbour one another without presenting points of any very profound dissimilarity? We have only a few isolated species, such as man, which form at once the species and the whole genus; the elephant, the rhinoceros, the hippopotamus, and the giraffe form genera, or simple species, which go down in a single line, with no collateral branches. All other races appear to form families, in which we may perceive a common source or stock from which the different branches seem to have sprung in greater or less numbers according as the individuals of each species are smaller and more fecund."[125] I can see no explanation of the introduction of this passage unless that it is intended to raise the question whether modification may be not only specific but generic, the point of the paragraph lying in the words "dans chaque famille, _ou si l'on veut, dans chacun des genres_." We are told in the next paragraph, that if we choose to look at the matter in this light, well--in that case--we ought to see not only the ass and the horse, but _the zebra too_, as members of the same family; "the number of their points of resemblance being infinitely greater than those in respect of which they differ."[126] Thus, at the close of his work on the quadrupeds, he thinks it well, as at the commencement seventeen years earlier, to emphasize--in his own quiet way--his perception that the principles on which he has been insisting should be carried much farther than he has chosen to carry them.