( cxviii ) 



irregular, uncertain, or even wanting. Caterpillars are 

 provided with beautiful protective adaptations, but the suc- 

 cessful 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.* 



The Instincts of Insects. — Those who advocate the hereditary 

 transmission of acquired characters have made great use of 

 the argument that the wonderfully complex and precise 

 adaptive instincts of insects require for their production the 

 accumulation of experience and of effort through n^any 

 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." f 



We observe in the first place that the Lamarckian interpreta- 

 tion 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 progress. 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 mechanically 

 by instinct. This is an inversion of the probable course of 

 evolution : the less efficient instrument has assigned to it by 

 far the moi'e difficult task. 



Apart from this pi'imd facie objection there are solid 

 grounds for the belief that the exqviisitely perfect operations 

 of insects with which we are familiar arose as instincts, as 



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

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

 t " Animal Behaviour," London, 1900, p. 120. 



