Similarity of Adaptations in Different Species 207 



cussed, it may merely be remarked here that the existence 

 of these like properties, acquired in the most different 

 species, is easier to explain by the Lamarckian theory than 

 by natural selection. For just as substances exposed, for 

 example, to identical calorific influences finally all take 

 on the same degree of temperature, and yet all remain 

 quite different from one another in other characters, 

 so when quite different species are exposed, on account 

 of the environment, or nourishment, or peculiar condi- 

 tions of light, or of any other cause whatever, to func- 

 tional stimuli which incite them, for example, to secrete 

 tannic acids or alkaloids, and so on, these secretions, 

 acquired by means of functional adaptation and trans- 

 mitted later by heredity, must come to be present in 

 several species, 'even though all other characters can 

 remain different. 



Here it seems to us, there remains for Weismann 

 nothing else than to affirm that these like characters 

 may have been fixed by natural selection in the most 

 different species because, from the likeness of the func- 

 tional stimuli to which, according to the hypothesis, these 

 species were exposed, the same characters must have 

 been the most useful for every one without exception. 

 But this must first be proved. And so much the more 

 since in this case it is more difficult than in other cases 

 to see the absolute necessity that all characters or pecu- 

 liarities whatever, which are due to the reaction of the 

 organism to the most different external influences and 

 often to insignificant ones, must always be useful to 

 the individual, and that therefore they must also possess 

 this utility even when they are produced rather by means 

 of inborn fortuitous variations. 



If the soundness of this conception, required by the 



