THE MEANING OF EVOLUTION 279 



We must recognise that our knowledge that other 

 beings like ourselves, as well as animals lower in organi- 

 sation than ourselves, are consciously acting organisms 

 is intuitive knowledge, attainable because of community 

 of organisation : our intuitive knowledge of the be- 

 haviour and feelings of our own brothers and sisters 

 is greater than our knowledge of other men and women ; 

 and we can, by intuition, place ourselves within the 

 consciousness of an intelligent dog to a greater extent 

 than in the case of other animals. This knowledge of 

 the consciousness of other animals is not scientific 

 knowledge and it is unattainable and unprovable by 

 reasoning or methods of scientific observation. It is 

 a conviction in itself incapable of analysis or proof, 

 but yet a conviction on which we confidently base 

 most of our dealings with our fellow-creatures, and 

 which is justified by our experience. 



It is nevertheless a scientific hypothesis of much 

 the same validity as many other scientific hypotheses. 

 We cannot bring ourselves to doubt that other men 

 and women are consciously acting organisms, however 

 impossible it may be to adduce scientific reason for the 

 faith that is in us. We cannot doubt that a compass 

 needle which ' ' responds ' by turning one or other of 

 its poles towards us according as we push forwards one 

 or other of the poles of a magnet is an unconscious piece 

 of metal, though we find it impossible to say why this 

 belief possesses such conviction. From this to the 

 movements of the typical green plant is only a step. 

 The turning of a green leaf towards the source of light, 

 or the downward movement of a root into the soil, are 

 responses to external stimuli which exhibit most of the 

 inevitability of response of the magnet. They are 

 ' tropisms " : the plant leaf is obliged to turn towards 

 the light so that the latter strikes against its surface 



