His views were preceded by two premises.
The species is only "_fixe sous la raison du maintien de l'etat conditionnel de son milieu ambiant_." It is modified, it changes, if the environment (_milieu ambiant_) varies, and according to the extent (selon la portee) of the variations of the latter.[146] As the result, among recent or living beings there are no essential differences as regards them--"_c'est le meme cours d'evenements_," or "_la meme marche d'excitation_."[147] On the other hand, the _monde ambiant_ having undergone more or less considerable change from one geological epoch to another, the atmosphere having even varied in its chemical composition, and the conditions of respiration having been thus modified,[148] the beings then living would differ in structure from their ancestors of ancient times, and would differ from them according "to the degree of the modifying power."[149] Again, he says, "The animals living to-day have been derived by a series of uninterrupted generations from the extinct animals of the antediluvian world."[150] He gave as an example the crocodiles of the present day, which he believed to have descended from the fossil forms.
While he admitted the possibility of one type passing into another, separated by characters of more than generic value, he always, according to his son Isidore, rejected the view which made all the living species descend "_d'une espece antediluvienne primitive_."[151] It will be seen that Geoffroy St.Hilaire's views were chiefly based on palaeontological evidence.

He was throughout broad and philosophical, and his eloquent demonstration in his _Philosophie anatomique_ of the doctrine of homologies served to prepare the way for modern morphology, and affords one of the foundation stones on which rests the theory of descent.
Though temporarily vanquished in the debate with Cuvier, who was a forceful debater and represented the views then prevalent, a later generation acknowledges that he was in the right, and remembers him as one of the founders of evolution.
FOOTNOTES: [125] Mr.Morley, in his _Rousseau_, gives a startling picture of the hostility of the parliament at the period (1762) when Buffon's works appeared.

Not only was Rousseau hunted out of France, and his books burnt by the public executioner, but there was "hardly a single man of letters of that time who escaped arbitrary imprisonment" (p.

270); among others thus imprisoned was Diderot.

At this time (1750-1765) Malesherbes (born 1721, guillotined 1794), one of the "best instructed and most enlightened men of the century," was Directeur de la Libraire.