204 Address to the British Association 



These reflections lead me to urge upon such of my hearers 

 as may have any unusual facilities for experimental investi- 

 gation, a course of inquiry which seems to be very desirable. 



What is needed in order to solve as far as possible the 

 question of specific genesis, is a knowledge of the laws of 

 variation, which must, I think, be deemed the true cause and 

 origin of species. 



We may, I think, accept as true two propositions : — 



(1) Animals may change in various ways, and amongst 

 them, by degradation. 



(2) Changes in the environment with isolation, induce 

 and favour changes in form. 



I would urge, then, that inquiries should be pursued in 

 two directions simultaneously. 



(A) There might be undertaken one set of inquiries to 

 investigate the effects on different species of the same varia^ 

 tions of environment. 



(B) Other inquiries might be undertaken with a view to 

 ascertaining the effects of different changes of environment 

 on one and the same species. By series of experiments con- 

 trived with these ends in view, and carried on with various 

 selected animals and plants which reproduce with rapidity, 

 we may possibly be able to determine what to attribute to 

 external influences (shown by such influences having the 

 same effects on all), and what to the pecuHar nature and 

 innate powers and tendencies of different organisms — shown 

 by the diverging reactions of the latter under the same 

 changes in their environment. 



I next desire to direct your attention to another matter 

 treated of by Buffon — I mean the resemblances and dif- 

 ferences WHICH EXIST BETWEEN THE MIND OF MAN AND THE 

 HIGHER PSYCHICAL FACULTIES OF ANIMALS. 



This question is eminently a question of our own day, and 

 one which I feel cannot but excite interest in this Section. 



