196 APPENDIX 



in a species whose members are highly plastic and rapidly responsive, the 

 adaptive innate characters, which may later be produced, will probably be 

 of a type different from that of those ontogenetically acquired. In other 

 words, the greater the plasticity, the less intimate will be its guidance of the 

 course of evolution, for a rapidly acquired and highly developed ontogenetic 

 adaptation is almost as beneficial as an innate adaptation of the same type. 



Note further that it is in cases of change in the environment, or change in 

 the habitat of the species, that the chief influence of plasticity upon evolution 

 is felt. When the environment remains unchanged, evolution is less rapid 

 and the influence of plasticity is also less. 



Were the author to state dogmatically his belief as to the role of plasticity 

 in evolution, he would say : The accommodation of the individual to adverse 

 conditions is of great importance in enabling the species to survive during 

 a period of temporary disadvantage; it may serve in a general way to guide 

 the course of evolution, but this guidance is not intimate and exact; in the 

 case of species whose members are highly plastic, it is an important hindrance 

 to the evolution by selection of qualities of similar use to those in which the 

 plasticity is shown. 



Of course plasticity is itself a very useful quality under many conditions 

 and will be developed through natural selection. 



