MAMMALS 79 



activity itself; it is only the psychological factor, the 

 joy of power, that often makes its appearance in it, 

 that justifies one in speaking of it as a species of 

 play. We shall see something about its nature in 

 the next chapter. 



In pursuing at such length these observations on 

 the play of animals, and taking our cue sometimes 

 from the life of man, we have not passed the limits 

 of this work. We have learned that many qualities 

 of mind that seem to belong to man alone are also 

 found in the animal. This shows us how untenable 

 is the opinion of those who think they have found 

 in man's mental powers something that distinguishes 

 the lord of creation essentially from other organisms 

 something that makes the descent of man from 

 other animals impossible. We now know that the 

 theory of evolution need not stop short at man ; that 

 even his mind is no obstacle to our admitting his 

 development from animal ancestors. The mind of 

 man does not differ from that of other animals in 

 kind but only in degree, and there is nothing to 

 prevent us from supposing that it has been raised 

 from the animal level by natural selection to its 

 present altitude. Just as Copernicus smote the 

 conceited belief out of humanity that their kingdom, the 

 earth, was the centre of the world, so Darwin has 

 put an end to their assumption that they occupy an 

 exceptional position on our planet. The earth is a 

 stage of a part of the eternal, everchanging world-mass ; 

 humanity is a phase of a part of the ever-advancing 

 world of organic life. 



