266 DARWINISM TO-DAY. 



more conspicuousness than Lamarck did. He did, indeed, 

 make some reference to the possible volitional effort of the 

 organism to change along certain desirable lines, but it is 

 evident that Lamarck had more in mind the animal's desires 

 and needs to stretch up higher for leaves or to dig better or 

 run faster, leading to actual attempts to do these things, than 

 to any expected results of mere mental wishing or willing. 

 The essential principle of Lamarckism is an orthogenetic 

 evolutionary progress toward better and finer adaptation and 

 adjustment resulting from the inherited effects of actual use, 

 disuse, and functional stimulation of parts. It is a great 

 thought and a clear one, and only needs the proof of the 

 actuality of the inheritance of individually acquired char- 

 acters to make it one of the principal causal explanations 

 of adaptation and species change. 



However, it is exactly this proof that is wanting. At any 

 rate, proof of the character and extent necessary to con- 

 vince all or even a majority of biologists is 



Weismann's J ' 



successful attack wanting. The examples or cases brought for- 

 onLamarckism, ward by L amar dd ans of the alleged inheritance 

 of mutilations, of the results of disease, and of use and 

 disuse, are not convincing. It is one of Weismann's posi- 

 tive contributions to biology to have analysed case after 

 case of alleged inheritance of acquired characters, and shown 

 its falseness or at least uncertainty. Many of these cases 

 he has been able to explain as a result of selection; others 

 remain inexplicable; a few, 2 only, are insisted on by the 

 Lamarckian champions as indisputable examples of such 

 inheritance. But this very paucity of so-called proved 

 cases, where there should be thousands of obvious ex- 

 amples if the principle were really sound, is argument against 

 Lamarckism. 



Our knowledge, too, of the mechanism of heredity makes 

 strongly against the theory of the inheritance of acquired 

 characters. Another of Weismann's positive contributions 



