Origin of Different Kinds of Adaptations 355 



The most obvious interpretation is that the degeneration has 

 been the result of disuse. But as I have already discussed 

 this question, and given my reasons for regarding it as im- 

 probable that degeneration has arisen in this way, we need 

 not further consider this point here. 



The selectionists have offered several suggestions to 

 account for degeneration. In fact, this has been one of the 

 difficulties that has given them most concern. They have 

 suggested, for example, that when an organ is no longer of 

 use to its possessor it would become a source of danger, 

 and hence would be removed through natural selection. 

 They have also suggested that since such organs draw on the 

 general food supply they would place their possessor at a 

 disadvantage, and hence would be removed. Weismann has 

 attempted to meet the difficulty by his theory of "Panmixia," 

 or universal crossing, by which means the useless structures 

 are imagined to be eliminated. 



These attempts will suffice to point out the straits to 

 which the Darwinians have found themselves reduced, and 

 we have by no means exhausted the list of suggestions that 

 have been made. Let us see, if, on any other view, we can 

 avoid some of the difficulties that the selection theory has 

 encountered. 



In the first place we shall be justified, I think, in eliminat- 

 ing competition as a factor in the process, since the admis- 

 sion that an organ has become useless carries with it the 

 idea that it has no longer a selective value. If, in its useless 

 condition, it is no longer greatly injurious, as is probably, 

 though not necessarily always, the case, then selection can- 

 not enter into the problem. If in parasitism we assume that 

 an animal finds a lodgement in another animal, where it is 

 able to exist, we may have the first stage of the process 

 introduced at once. If under these conditions a mutation 

 appeared, involving some of the organs that are no longer 

 essential to the life of the individual in its new environment, 



