THE WONDER OF LIFE 515 



quired adaptive modifications, which are the direct results 

 of changes in the ordinary nurture, could not occur unless 

 the potentiality of them were part of the heritable ' nature '. 

 That goes without saying, but it does not affect the clear 

 distinction between the exogenously induced modification, 

 wrought from without inwards, and the endogenously 

 originating variation which works from within outwards. 

 Origin of Adaptations. Like the correlated but larger 

 problem of the origin of species, this is one of the funda- 

 mental still imperfectly answered questions which the 

 interpreter of animate nature has to face. There are only 

 two main theories in the field the theory of the direct, 

 and the theory of the indirect origin of adaptations. 



(a) According to the Lamarckian theory racial adapta- 

 tions owe their origin to the cumulative inheritance of 

 individual adaptive modifications. But there is as yet a 

 lack of positive evidence in support of this interpretation, 

 plausible as it seems to be. Unless we have experimental 

 evidence of the transmissibility of presently occurring 

 adaptive modifications, we are not justified in using this as 

 an interpretation of results which occurred in the distant 

 past. Too much may be made of the argument that 

 many cases are known where transmission of modifica- 

 tions certainly does not occur, but it must be admitted 

 that it is difficult in our present state of knowledge to 

 conceive of any way by which a change acquired by a 

 part of the body can affect the germinal material in a 

 manner so precise and representative that the offspring 

 show a corresponding change in the same direction. 



(b) The Darwinian theory is that adaptations are due 

 to the selection of those inborn and heritable variations 

 which, by making their possessors better adapted to the 



