Origin of Different Kinds of Adaptations 379 



Nevertheless, it seems to be true in the case of morphine and 

 of arsenic, and probably for some other substances as well, 

 that if their use is suddenly stopped the individual may die 

 in consequence. In this respect the organism behaves ex- 

 actly as it does to an environment to which it has become 

 adapted. 



Regeneration 



Many animals are able to replace lost parts, and all of 

 them can heal wounds and mend injuries. This power is 

 obviously of great advantage to them, and it has been sup- 

 posed by Darwin, and more especially by his followers, that 

 the power has been acquired through natural selection. It 

 is not difficult to show that regeneration could not, in many 

 cases, and presumably in none, have been acquired in this 

 way. Since I have treated this subject at some length 

 recently in my book on "Regeneration," I shall attempt to 

 do no more here than indicate the outline of the argument. 



The Darwinians believe that, if some individuals of a 

 species have the power to replace a part that is lost better 

 than have other individuals, it would follow that those would 

 survive that regenerate best, and in this way after a time the 

 power to regenerate perfectly would be acquired. 



But the matter is by no means so simple as may appear 

 from this statement. In the first place, it is a matter of 

 common observation that all the individuals of a species are 

 never injured in the same part of the body at the same time. 

 In those cases in which it is known that a special part is 

 often injured, an examination has shown that there are not 

 more than ten per cent of individuals that are injured at any 

 one time, and in the case of the vast majority of animals 

 this estimate is much too great. Thus there will be very 

 little chance for competition of the injured individuals in 

 each generation with each other, and the effects that are 

 imagined to be gained as a result would be entirely lost 



