i54 INSECTS AND HEREDITY 



an individual are relative to the condition of the organic 

 environment with which its contact is in many respects 

 irregular, uncertain, or even wanting. Caterpillars are 

 provided with beautiful protective adaptations, but the 

 successful individual never comes into contact with an 

 enemy. But there is an environment which the organism 

 cannot avoid — the physico-chemical stimuli of climate 

 and food ; and it is presumably here, in the inorganic 

 conditions of life, that the influences which bear a pre- 

 eminent part in evoking useful variations are supposed 

 to reside. So that stimuli provided by one form of 

 environment are looked upon as the direct causes of 

 adaptations which are essentially related to another and 

 very different environment. 1 



The Instincts of Insects. 



Those who advocate the hereditary transmission of 

 acquired characters have made great use of the argu- 

 ment that the wonderfully complex and precise adaptive 

 instincts of insects require for their production the 

 accumulation of experience and of effort through many 

 generations. Only by such transmission, they maintain, 

 is it possible to understand such development. 



It is safest to begin with a definition, and I accept 

 the brief, convenient, and in my opinion entirely accurate, 

 statement of Lloyd Morgan : ' Instinct depends on how 

 the nervous system is built through heredity; while 

 intelligence depends upon how the nervous system is 

 developed through use.' 2 



We observe in the first place that the Lamarckian 

 interpretation places the more difficult phases of the 

 evolution of instinct — the phases when it was not 

 instinct at all but something much higher — in some 

 remote epoch of the past, and at a lower level of pro- 

 gress. In such times, ex hypothesi, the less developed 

 and presumably less efficient brains of insects did by 

 the intelligent use of experience what they now do 



1 The substance of the argument set forth in this paragraph was 

 published by the writer in Nature, vol. 1, 1894, p. 445. 

 Animal Behaviour, London, 1900, p. 120. 



