INTRODUCTION 41 



the heads of the fighting stags against each other during the 

 rutting season, and afterwards developed constantly by the 

 strains of the antlers of the combatants against each other, 

 then the hereditary tendency to the periodic annual growth 

 of the antlers would be an intelligible fact. It cannot be too 

 strongly emphasised that hitherto no attempt has been made 

 to give an explanation of such facts as these. The theory 

 that I advocate does explain them, while on all other theories 

 of evolution the occurrence of the variations is merely 

 assumed, and no reason for the peculiar modes and times of 

 their occurrence is even offered. I believe I may claim that 

 my theory is, in its special details, new and original. The 

 theory of the inheritance of acquired characters is, of course, 

 old, and regarded by many as even extinct. But so far as I 

 know I have not been anticipated in my elaboration of this 

 theory into the form in which I present it, namely, that the 

 direct effects of regularly recurrent stimulations are sooner or 

 later developed by heredity, but only in association with the 

 physiological conditions under which they were originally pro- 

 duced, and that this is the explanation of the limitation of 

 particular modifications, not merely to particular species or 

 kinships, but to particular periods in the life of the individual, 

 to a particular sex, and even to a particular season of the 

 year in that sex. 



It may be objected to my argument that I have not proved 

 that particular stimulations actually produce the effects I 

 attribute to them, and still less that any such effects are 

 ever inherited. Such an objection would show a complete 

 misunderstanding of my object in this work and my method 

 of reasoning. Experimental investigations of the direct effects 

 of stimulations have been made and published, by myself 

 among many others. 1 That stimulations do produce local 



1 See Coloration of Pleuronectidce, Cunningham and MacMunn. Phil. 

 Trans., 1896. 



