REGENERATION 61 



To know that the presence of a certain organ may lead 

 to the preservation of a race is useless if we cannot tell 

 how much preservation it can effect, how many indi- 

 viduals it can save that would otherwise be lost ; unless 

 we know also the degree to which its presence is 

 harmful ; unless, in fact, we know how its presence 

 affects the profit and loss account of the organism.'* 



A great many other criticisms and objections have 

 been brought at various times against the theory of 

 the origin of adaptations by the action of natural 

 selection, and many of these were considered and 

 replied to by Darwin in the later editions of the ' Origin 

 of Species.* We shall only consider here a few which 

 have been put forward more or less recently. Before 

 doing so it will be well to point out once more that no 

 one questions the validity of natural selection as a means 

 of exterminating types which are unfitted for their 

 environment there is clearly a tendency for the 

 fittest types to survive once they have come into 

 existence. Nor can there be any doubt that species 

 in general are well adapted to the conditions which 

 their environments present. But when this is admitted 

 it does not necessarily follow that natural selection, 

 directing the accumulation of minute differences, has 

 been the method by which these adapted forms have 

 originated. 



The power of regenerating a lost part must clearly 



often be of service to the creatures which possess it. 



Such a power may in many cases be considered to be 



a well-marked adaptation. But* as Morgan has well 



* W. Bateson, ' Materials for the Study of Variation,' p. 12* 



