Are Acquired Habits inherited? 285 



though, if the trimming arise from some defect in the 

 feathers, all that is necessarily inherited is such congenital 

 deficiency. 



It would seem, then, to revert to our main theme, that 

 so far as the activities and behaviour of animals are con- 

 cerned, evolution is tending to produce two things- 

 congenital uniformity and innate plasticity ; if we may use 

 this latter term for susceptibility to modification by the 

 intelligent utilization of experience. Both are due to 

 heredity; but whereas the one, congenital uniformity, 

 presents a certain amount of initial definiteness, the other, 

 innate plasticity, is in its nature initially indefinite ; 

 whereas the former, the initial definiteness, has its 

 origin in past uniformity of response; the latter, sus- 

 ceptibility to modification, allows of future variety of 

 response ; and whereas the definiteness is specific and 

 racial, the plasticity allows of individualism. The two are 

 to a certain extent antagonistic, and to a certain extent 

 complementary. Evolution has to strike a balance between 

 them ; to hit the happy mean between a congenital uni- 

 formity which leaves no room for individual adaptation, 

 and an innate plasticity that is devoid of sufficient 

 stability. 



To these two, however, a third must be added when 

 the whole life of an organism is taken into consideration. 

 Just as hereditary stability as it is seen in the uniform 

 performance of definitely instinctive activities is in contrast 

 with the individual plasticity shown in the phenomena of 

 adaptation to new circumstances, so too is the relative 

 plasticity of the young in contrast with the relative stability 

 of the old. We have to take into account acquired stability 

 due to habit as well as congenital stability due to heredity. 

 The three factors are, therefore, (1) congenital stability, 

 (2) youthful plasticity, and (3) acquired stability. Now, 



