SOME EIGHTEENTH CENTURY EVOLUTIONISTS. 325 



outspoken ; and in his ' Pensees de Interpretation de la Nature ' he 

 declared plainly that the doctrine of the mutability of species and of 

 their descent from a common prototype was, if not an established truth, 

 at any rate a legitimate and a necessary working hypothesis for all 

 future biological investigation. 



The most interesting and most explicit passage on the subject in 

 the ' Pensees ' has, so far as I know, been noted by no English writer ;* 

 and I therefore translate it without abridgment. " It seems/' says 

 Diderot, "that nature has taken pleasure in varying the same mechan- 

 ism in a thousand different ways. She never abandons any class of 

 her creations before she has multiplied the individuals of it in as many 

 different forms as possible. When one looks out upon the animal 

 kingdom and notes how, among the quadrupeds, all have functions and 

 parts — especially the internal parts — entirely similar to those of 

 another quadruped, would not any one readily believe (ne croirait-on 

 pas volontiers) that there was never but one original animal, prototype 

 of all animals, of which Nature has merely lengthened or shortened, 

 transformed, multiplied or obliterated, certain organs? Imagine the 

 fingers of the hand united and the substance of the nails so abundant 

 that, spreading out and swelling, it envelops the whole — and in place 

 of the human hand you have the foot of a horse. When one sees how 

 the successive metamorphoses of the envelope of the prototype — what- 

 ever it may have been — proceed by insensible degrees through one 

 kingdom of Nature after another, and people the confines of the two 

 kingdoms (if it is permissible to speak of confines where there is no 

 real division) — and people, I say, the confines of the two kingdoms 

 with beings of an uncertain and ambiguous character, stripped in large 

 part of the forms, qualities and functions of the one and invested with 

 the forms, qualities and functions of the other — who then would not 

 feel himself impelled to the belief that there has been but a single first 

 being, prototype of all beings? But whether this philosophic con- 

 jecture be admitted as true with Doctor Baumann [Maupertuis], or 

 rejected as false with M. de Buffon, it can not be denied that we must 

 needs embrace it (on ne niera pas qu il faille I'embrasser) as a hypo- 

 thesis essential to the progress of experimental science, to that of a 

 rational philosophy, to the discovery and to the explanation of the 

 phenomena of organic life" (op. cit., XII.). If the rest of the passage 

 left any uncertainty as to the precise nature of the hypothesis that 

 Diderot had in mind, the reference to Maupertuis and Buffon would 

 make his meaning unmistakable. 



* Osborn cites only another and less explicit passage from Diderot; and 

 Mr. John Morley ('Diderot and the Encyclopaedists'), although he notes a hint 

 of the idea of natural selection in the ' Lettre sur les Aveugles ' (1749), says 

 nothing about the marked evolutionism of the ' Pensees de l'lnterpretation de la 

 Nature.' 



