LIFE; BODY AND MIND 197 



earth's surface, and he might speculate, as we 

 now speculate, in vain, asking whether this was 

 a gradual development of processes which he 

 had formerly failed to recognize, or whether 

 the germ of some new thing had drifted in from 

 extraterrestrial space. We see no way of an- 

 swering this or the related question as to 

 whether life was born only once upon the earth 

 or has begun many times and may even now be 

 beginning again. The identity of the mechanism 

 of reproduction in plants and animals, which I 

 mentioned in the last chapter, strongly indi- 

 cates that at least the higher forms of life had 

 a single origin. The dodo once extinct will never 

 be seen again, and if all existing life should 

 become extinct we have no way of guessing 

 whether this particular kind of complexity in 

 nature would ever reappear. 



Shall I now be called a vitalist if I say that 

 many of the phenomena of life may be studied 

 by methods which, while truly scientific, are en- 

 tirely independent of the methods of geometry, 

 mechanics and chemistry? Of these phenomena, 

 which have no counterpart, as far as we know, 

 in inanimate nature, one of the most striking is 

 known as the struggle for existence, an idea 



