156 DARWINISM TO-DAY. 



creasing adaptability of the organisms, or both, certain 

 major essential adaptations, which were necessary for the 

 climatic and other more or less comparatively simple con- 

 ditions, will be supplemented by minor auxiliary variations 

 which in the earlier stages would not have appeared. And 

 still later, as more and more rigorous conditions of life were 

 imposed, the advantage would tend to rest with those organ- 

 isms which possessed highly coordinated adaptations, since 

 this would entail more rapid responsiveness to environment. 

 "As evolution advances from the unspecialised to the spe- 

 cialised, and higher and higher forms of life come into 

 being, with increasing complexity and specialisation of parts 

 entailing an increasingly delicate adjustment of those parts 

 to each other's needs, the relation of each part to the whole 

 organism becomes of more and more importance, and it 

 follows that selection must become more and more general- 

 ised in its action. No single variation could be of service 

 to any of the higher forms of life unless it was in more or 

 less complete harmony with the whole tendency of the 

 individual. The adjustment of parts and their mutual inter- 

 dependence make it essential for adaptation that the relation 

 of parts be preserved; consequently, correlated minute 

 favourable variations will tend to be more and more selected 

 as evolution passes from the unspecialised to the specialised 

 forms of life. This response of the whole organism should 

 be still more delicate in those forms of life that are con- 

 tinually subjecting themselves to changed conditions; hence 

 this delicacy of adjustment is far more necessary in the 

 higher forms of animal life than in the more stationary plant 

 organisms, and in the developing nervous system of animals 

 we have just the central adjusting system that is required for 

 these conditions. With evolution of type there will thus be 

 an increasingly definite tendency given to organic, espe- 

 cially the animal, forms of life, if the acting principle of 

 evolution has been selectional. Selection is, therefore, able 



