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SCIENCE 



[N. S. Vol. XLIII. No. 1112 



succeed one another, derived to be sure one 

 from another, but following a succession 

 that is really determined in advance and 

 independent of external contingencies. Be- 

 tween such views there is in reality no con- 

 siderable difference. Such an idea substi- 

 tutes for successive creations one initial 

 creation with successive and continuing 

 manifestations. The present crisis of trans- 

 formism, as Le Dantec and others set it 

 forth, is the conflict concerning the recip- 

 rocal value of external and internal factors 

 in evolution. 



The two principal and classic solutions 

 proposed to explain evolution were based 

 on the efficacy of external factors, both the 

 theory advanced by Lamarck in 1809 in his 

 "Philosophic Zoologique," as well as that 

 of Darwin formulated in 1859 in "The 

 Origin of Species." Lamai'ck starts in fact 

 with the statement that the structure of 

 organisms is in harmony with the condi- 

 tions under which they live and that it is 

 adapted to these conditions. This adapta- 

 tion is, in his opinion, not an a priori fact 

 but a result. The organism is shaped by 

 the environment ; usage develops the organs 

 in the individual; without usage they be- 

 come atrophied. The modifications thus 

 acquired are transmitted to posterity. 

 Adaptation of individuals, inheritance of 

 acquired characteristics, these are the fun- 

 damental principles of Lamarckism. Ex- 

 cept for its verification, it is the most com- 

 plete scientific theory of transformism 

 which has been formulated, because it looks 

 to the very cause of the change of organisms 

 by its method of explaining adaptation. 

 Darwin adopted the idea of Lamarck and 

 admitted theoretically adaptation and the 

 inheritance of acquired characteristics, but 

 he accorded to them only a secondary im- 

 portance in the accomplishment of evolu- 

 tion. The basis for him is the variability 

 of organisms, a general characteristic whose 



mechanism he did not try to determine and 

 which he accepts as a fact. This being so, 

 the essential factor of the gradual trans- 

 formation of species is the struggle for life 

 between the individuals within each species 

 and between the different species. The 

 individuals which present advantageous 

 variations under the conditions in which 

 they live have more chance to survive and 

 to reproduce themselves; those which on 

 the contrary offer disadvantageous varia- 

 tions run more chance of being suppressed 

 without reproducing themselves. There is 

 established then automatically a choice be- 

 tween individuals, or, according to the ac- 

 cepted terminology, a natural selection, a 

 choice which perpetuates the advantageous 

 variations and eliminates the others. And 

 with this going on in each generation the 

 type is transformed little by little. Natural 

 selection accumulates the results of varia- 

 tion. 



This is not the time to discuss Darwin's 

 theory. I wish only to observe to-day that 

 it is less complete than that of Lamarck in 

 that it does not try to discover the cause of 

 variations ; also that, like that of Lamarck, 

 it attributes a considerable participation to 

 the conditions outside the organism, since 

 it is these finally which decide the fate of 

 the variations. And one of the forms in 

 which the opposition to the transformist 

 ideas, at the time of Darwin, manifested It- 

 self, was the very argument that if organ- 

 isms had varied it was only because of an 

 internal principle, as Kolliker and Nageli 

 have more particularly explained. 



The biologists at the end of the nine- 

 teenth century were divided with regard 

 to the mechanism of evolution, into two 

 principal groups, following either Lamarck 

 or Darwin. Among the neo-lamarckians 

 some have accorded to natural selection 

 the value of a secondary factor, holding 

 that the primary factors are the direct 



