PRINCIPAL ATTEMPTS AT EXPLANATION 153 



only specific similarity is determined by common 

 descent, as actual practical observation shows. Palaeon- 

 tology certainly renders it probable that also fairly 

 different animals may descend from common ancestors. 

 This difference was acquired through differentiation 

 and specialization, but always within narrow limits. 

 Never, however, do the fossils found demand the 

 assumption that a higher class arose from a lower 

 one, to say nothing of one family arising from another, 

 or, in the extreme, animals from plants. 



(b) That the ' psyches ' of man, the animals and plants, 

 are only a perfection of the same fundamental faculties 

 of all organisms is altogether false. In the first place 

 the soul of man and also those of animals and plants 

 cannot be regarded as ( perfections ' of matter : they 

 are substantial components of the organisms. There 

 is an essential difference between a ' psyche ' which 

 thinks and shows a free self-determination (the human 

 soul) and one whose faculties do not extend beyond 

 the provision of sensitive recognition and sensitive 

 endeavour (the animal soul). With us the senses do 

 not suffice for thought and free-will, nor do they with 

 animals, and never, really never, is there to be observed 

 anything of the sort with them. Has not the entire 

 modern animal psychology been written also for 

 the psychobiologists ? (Wundt, Thorndike, Hobhouse, 

 Morgan, Stumpf, Wasmann). 



The same applies to the difference between animal 

 and plant souls. That plants respond to the same 

 external stimuli otherwise than do inorganic bodies, 



