In Buffon’s last opinion[292] species was not that definite entity in which Cuvier believed, commencing at a given geological moment, in order to terminate at another. Buffon says, in his latest works, that the idea of species can only be seized upon by man at “this or that instant of his age,”[293] and that it is merely the expression of the ambient medium. Let this remain as before, it will not change; but when the conditions of the medium become modified, _species_ will change. We thus arrive at this definition:-- DEFINITION.--“_Species is a collection or group of individuals characterised by a similarity of distinctive points; the transmission of which is accomplished naturally, regularly, and indefinitely, in a given order of things._”[294] It is, in more scientific terms, the definition by Lamarck, “a collection of similar individuals which generation perpetuates in the same state, so that the circumstances of their situation do not sufficiently alter so as to make their habits, their character, or their form vary.”[295] Lamarck, to whom Isidore Geoffroy has rendered greater justice than any one else before or after him,[296] admitted the _unlimited variableness of species_. He admitted that we all descend, just as we are, from an anatomical element, developed in a determinate sense, and that we may have been worms, insects,[297] birds, and mammals before becoming men, running through all the phases through which animal organisation has passed during our uterine life. We see that Lamarck approached frankly and resolutely the problem of the origin of humanity. In taking but superficially certain exaggerations into which Lamarck fell, at a time less rich in facts than our own, it is not difficult to give a certain grotesque turn to his ideas, and to laugh at them as being unnatural; but we must not thus judge the work of a man’s whole life, and we must appreciate Lamarck by the basis of his doctrine more than by the examples he has given us: “a profound philosopher,” said Étienne Geoffroy,[298] “able in laying down principles, less able in the choice of his proofs.” We must judge Lamarck as Isidore Geoffroy has done in his _Histoire Naturelle Générale_, where we find a complete and impartial chronological statement concerning the grave question of species.[299] “Circumstances have an influence upon form and organisation,” such is the fundamental principle of Lamarck’s doctrine;[300] he says the same elsewhere:[301] “Circumstances determine positively what each body may be;” and he concludes, “among living bodies, nature only shows individuals who succeed one another. Species, amongst themselves, are only _relative_, and are only temporarily so.”[302]