234 THE HrsTony of creation. 



plienomei^, which are usually divided into two quite 

 distinct groups. Naturalists, as a rule, have distinguished, 

 first, those variations of organisms which are produced 

 directly by the permanent influence of external conditions 

 (by the constant action of nutrition, of climate, of surround- 

 ings, etc.), and secondly, those variations which arise from 

 habit and practice, from accustoming themselves to definite 

 conditions of life, and from the use and non-use of organs. 

 The latter influences have been set forth especially by 

 Lamarck as important causes of the change of organic 

 forms, while the former have for a very long time been 

 recognized as such more generally. 



The sharp distinction usually made between these two 

 groups of cumulative adaptation, and which even Darwin 

 stiU maintains, disappears as soon as we reflect more 

 accurately and deeply upon the real nature and causal 

 foundation of these two, apparently very different, series 

 of adaptations. We then arrive at the conviction that in 

 both cases there are always two different active causes to 

 be dealt with : on the one hand the external influence or 

 action of adaptative conditions of life, and on the other 

 hand the internal reaction of the organism which subjects 

 and adapts itself to that condition of life. If cumulative 

 adaptation is considered from the first point of view alone, 

 and the transforming actions of the permanent external con- 

 ditions of life are traced to those conditions solely, then the 

 principal stress is laid unduly upon the external factor, and 

 the necessary internal reaction of the organism is not taken 

 into proper consideration. If, on the other hand, cumulative 

 adaptation is mijustly regarded solely in relation to its 

 second factor, and the transforming action of the organism 



