3 i4 THE POPULAR SCIENCE MONTHLY 



minded way, upon a question of far-reaching consequence. The dis- 

 putes and confusions which have so long entangled the question I 

 believe to be due to the failure to see certain practical, or common sense 

 aspects — the failure to distinguish between environments which are 

 greatly changed and those which are only slightly altered, between 

 those from which escape is impossible and those from which such es- 

 cape is relatively easy; the failure to distinguish between environments 

 which are expected and those which are not, and, lastly, perhaps most 

 important of all, the failure to distinguish between effects on higher 

 and on lower types and tissues. 



About ten years ago I became convinced through an extended 

 analysis of the genealogical and personal data which exist in histories 

 concerning the royal families of Europe that the influence of environ- 

 ment in creating mental and moral differences among human beings 

 had been greatly overestimated. This conclusion was arrived at from 

 various points of view. Statistical analysis not only supported a theory 

 of germ-cell, or innate causation, but, what was more compelling, an 

 intensive study of each separate family and each isolated group of 

 close relatives brought out such sharp contrasts among the close of kin, 

 such variations in types of mind and character, even when narrowly 

 environed in point of time and place, that a recourse to heredity be- 

 came forced upon me. The explanation from environment would not 

 work. 



This conclusion concerning the relatively slight or unimportant 

 influence of environment as a modifying force on the higher human 

 traits, I announced at the Chicago meeting of the American Psycho- 

 logical Association in 1901 ; since which time I have been constantly 

 on the lookout for any investigations which might either confirm this 

 belief or necessitate a change of faith. Several direct researches on 

 human heredity have appeared which have been confirmatory in one 

 way or another, and as far as I know nothing has been brought forward 

 to disprove even an extreme belief in the predetermined nature of psy- 

 chological differences; but it is not the human side of the question 

 that I wish to discuss so much as the results of experimental zoology 

 and botany and their significance to the student of man. 



From time to time a vast array of experimental proof has come to 

 my attention showing the profound effect of modification on plants and 

 animals. The word modification I use in its technical sense as pro- 

 posed by Lloyd Morgan to cover those changes which occur — in the life 

 time of an individual and known to be directly traceable to some 

 natural or artificial (usually artificial) change in its surroundings. 

 These modifications are known to occur and may be easily observed or 

 measured. Whether they are inherited or not is another question, and 

 one entirely outside of the present thesis, for I wish to treat solely of 



