this natural proceeding, a new variety can be formed, and may either supplant the parent species or coexist with it.[306] Such is, in a few words, the theory of natural selection. In our ideas, there is here a false interpretation of facts; we do not believe in this _chance_ of a native disposition, which thus transmits itself in order to become in time a specific characteristic. We have shown, while speaking of hybridity, that a native _individual_ disposition ought always to disappear by the mere fact of its being individual; it quickly disappears through cross-breeding at the tenth generation, if not at the first, in the midst of a population which does not possess it. We fully admit, like Lamarck, that species are formed from one another by the appearance of organic modifications, more or less decided; but we do not leave anything to chance in this phenomenon, as Darwin does, and we can only see there the application of general laws. It is not one or two animals, born with some special psychological or anatomical disposition, who are destined to generalise themselves by generation: it will be _all_ the individuals of the same species in a certain radius, who will be born with a scarcely appreciable organic modification, resulting, as far as we can tell, in an action of the medium also nearly inappreciable by ourselves, but which long ago will have made itself felt by the parents. The new variety will be propagated quite naturally, since it is general, and can but increase with each generation as long as the modifying cause continues to act. Étienne Geoffroy had been the worthy successor of Lamarck, with a larger and more philosophical mind. He never fell into his exaggerations, nor into the restrictive applications of the system, like Darwin. Let us see how Isidore Geoffroy[307] continues his father’s theory: “Species is variable under the influence of the ambient medium; differences, more or less considerable according to the power of the modifying causes, may in time be produced, and the present beings may be the descendants of the former being.” This doctrine is our own also.