The Mechanism of Adaptation 339 



that may be developed for violent poisons; such acclima- 

 tization or toleration cannot be due to the elimination on a 

 large scale of organisms that cannot become adapted, since 

 in well-conducted experiments few if any of the individuals 

 perish. In the case of bacterial toxins or snake venom, the 

 manner in which tolerance to the poison is brought about 

 is better understood than in the case of other poisons. It 

 is known that the body that is poisoned forms various anti- 

 bodies as antidotes to these poisons, and for every toxin, 

 or at least for every toxalbumin, its^particular anti-body; 

 but why a particular toxin causes the formation of its one 

 appropriate antitoxin is a mystery. Many of these toxins 

 are of such a sort that it is perfectly certain that the im- 

 mediate ancestors of the individuals poisoned could never 

 have had experience with them, as, for example, in the case 

 of guinea-pigs innoculated with cobra venom; and yet the 

 response is as perfect as it could be if it had been due to 

 long experience. Many other similar cases might be cited, 

 but these are enough to indicate how difficult it is to find a 

 natural explanation for these individual, contingent adapta- 

 tions. Indeed, it may be said that the apparently intelligent 

 and purposive response of an organism to a stimulus or 

 environment which it or its ancestors have never experienced 

 before is one of the most important and mysterious problems 

 of biology. 



Both Lamarckism and Darwinism hold that racial adap- 

 tations are due to experience ; Lamarckism, that they are the 

 directly inherited effects of individual experience; Darwin- 

 ism, that they are the indirect results of ancestral experience 

 operating through the presentation of many variations to 

 the action of natural selection and the survival of the better 

 adapted. Neither of these theories explains sudden adapta- 

 tions of individuals to conditions never experienced before. 



