248 POPULAR SCIENCE MONTHLY. 



winian theory of Pangenesis. All these ideas are put forward by Mau- 

 pertuis only as so many likely explanations of facts which, as he 

 insisted, needed more adequate analysis and explanation than the 

 embryological doctrines of the time afforded; his pangenetic theory, 

 in particular, he regarded only as une conjecture bien liardie, mais qui 

 ne serait peut-etre pas destitute de toute vraisemblance. 



What is noteworthy in these hypotheses is the group of truths which 

 they involve incidentally. From Maupertuis's exposition of them it is 

 clear that he had been led, by his reflections upon the facts of heredity, 

 to recognize (a) that there is a constant tendency to variation in ani- 

 mals by reason of their double heredity; (&) that there is a further 

 tendency to spontaneous and accidental variations, due in part to 

 mechanical displacements or chance combinations among the ultimate 

 particles of which the embryo is composed; (c) that these variations 

 — and possibly also new characters acquired during the lifetime of the 

 parent* — tend to be perpetuated through heredity, provided that they 

 do not unfit the animals that possess them for survival in their environ- 

 ment, and provided also that they are not gradually obliterated through 

 inter-breeding with animals that do not possess them. To one who 

 thus emphasized the factors making for variation and for the conserva- 

 tion of variations, the theory of the mutability of species necessarily 

 appeared more natural than the theory of their fixity. Maupertuis 

 thus passes at once from his theories of heredity to propound the 

 hypothesis that all species may have come from a single primitive pair 

 through the gradual accumulation and transmission of divergent 

 variations. Granting these facts about variation, he writes, "would 

 it not be possible to explain by means of them how the multiplication 

 of the most dissimilar species might be traced back to (aurait pu 

 s'ensuivre de) only two individuals. Such species would have owed 

 their origination merely to the accidental production of certain 

 embryos (a quelques productions fortuites) in which the elementary 

 parts had not retained the arrangement which they had had in the 

 parent animals. Each degree of deviation (erreur) would bring about 

 a new species; and by means of repeated departures from the original 

 form (a force d'ecarts repetes) there would have come about the infinite 

 diversity of animals that we see to-day : — a diversity which may in time 

 increase still further, but to which it may be that the lapse of centuries 

 will bring only imperceptible additions" ('Systeme de la Nature,' 

 XLV.). In the 'Lettres' Maupertuis again writes, a propos of the 

 inheritance of certain congenital individual variations in the human 



* Maupertuis raises the question concerning the inheritance of acquired 

 characters, but suspends judgment upon it, and calls for further experimenta- 

 tion. ' Ce serait assur£ment quelque chose qui meriterait bien l'attention des 

 philosophes, que d'6prouver si certaines singularity artificielles des animaux 

 ne passeraient pas, apres plusieurs generations, aux animaux qui naltraient de 

 ceux-lfi..' 



