BLENDED ORIGIN, OR PLASTICITY OF INSTINCT. 203 



this further development of an instinct, if the variations of 

 the instinct are not wholly fortuitous, but arise as intelligent 

 adaptations of ancestral experience to the perceived require- 

 ments of individual experience. 



Trusting then it is sufficiently clear that the two princi- 

 ples which may operate either singly or together in forming 

 instincts, may operate together whichever of the two may 

 happen to have, in any particular case, the historical priority, 

 I may in future neglect to entertain the question of such 

 priority ; without considering whether in this and that case 

 selection was prior to lapsing of intelligence, or lapsing of 

 intelligence was prior to selection, it will be enough to prove 

 that the two principles are conjoined. 



To prove this we have to show, much more copiously 

 than has been done in the above two or three illustrations, 

 not only, as was proved in the previous chapter, that fully 

 formed instincts may vary, but further that their variation 

 may be determined by intelligence. 



Plasticity of Instinct. 



In former publications I have used this term to express 

 the modi liability of instinct under the influence of intelligence. 

 I shall now give some chosen instances of such modifiability, 

 and then proceed to indicate the causes which most fre- 

 quently lead to intelligence thus acting upon instinct. It is 

 of importance that I should begin by rendering the fact of 

 tin- plasticity of instinct beyond question, not only because 

 it is still too much the prevalent notion that instincts are un- 

 alterably fixed, or rigidly opposed to intelligent alteration 

 under changed conditions of life; but also because it is this 

 principle of plasticity that largely supplies to natural selec- 

 tion those variations of instinct in beneficial lines, which are 

 necessary to the formation of new instincts of a primo- 

 secondary kind. 



Huber observes: "How ductile is the instinct of bees, 

 and how readily it adapts itself to the place, the circum- 

 stances, and the needs of the community." 



If this may be said of the animals in which instinct has 

 attained its h perfection and complexity, even without 



evidence we might be prepared to expect that instinct is 

 everywhere ductile. Moreover the bees constitute ag I 



