THE STORY OF NINETEENTH-CENTURY SCIENCE 



But as soon as the validity of the principle of natural 

 selection came to be acknowledged, speculators began to 

 search for the explanation of those variations which, for 

 purposes of argument, had been provisionally called 

 " spontaneous." Herbert Spencer had all along dwelt 

 on this phase of the subject, expounding the Lamarck- 

 ian conceptions of the direct influence of the environ- 

 ment (an idea which had especially appealed to Buffon 

 and to Geoffroy Saint-Hilaire), and of effort in response 

 to environment and stimulus as modifying the individu- 



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al organism, and thus supplying the basis for the opera- 

 tion of natural selection. Haeckel also became an advo- 

 cate of this idea, and presently there arose a so-called 

 school of neo-Lamarckians, which developed particular 

 strength and prominence in America, under the leader- 

 ship of Professors A. Hyatt and E. D. Cope. 



But just as the tide of opinion was turning strongly in 

 this direction, an utterly unexpected obstacle appeared 

 in the form of the theory of Professor August Weis- 

 mann, put forward in 1883, which antagonized the La- 

 marckian conception (though not touching the Darwin- 

 ian, of which Weismann is a firm upholder) by denying 

 that individual variations, however acquired by the ma- 

 ture organism, are transmissible. The flurry which this 

 denial created has not yet altogether subsided, but sub- 

 sequent observations seem to show that it was quite dis- 

 proportionate to the real merits of the case. Notwith- 

 standing Professor Weismann's objections, the balance 

 of evidence appears to favor the view that the Lamarck- 

 ian factor of acquired variations stands as the comple- 

 ment of the Darwinian factor of natural selection in ef- 

 fecting the transmutation of species. 



Even though this partial explanation of what Pro- 



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