162 INTRODUCTION TO SCIENCE 



implies a succession of chemical and physical 

 processes. But, as we have seen, the life of the 

 organism also implies a co-ordination, a purposive- 

 ness, an individuality, a creative agency, a power 

 of trading with time, a history in all of which 

 it transcends mechanism. Similarly, both the 

 vital and the physical overlap the psychical with- 

 out, as we understand it, affecting the autonomy 

 of psychology. 



Looking at the question historically, we recog- 

 nize that there was for millions of years, in the 

 development of the earth, only a physical order 

 as far as met the eye. That is to say, everything 

 (short of the origin of life) that happened during 

 these millions of years was capable of descrip- 

 tion in physico-chemical terms. These are so 

 " true to Nature" that just as we can predict the 

 return of a comet, so in many cases we can safely 

 speak of great events that occurred before there 

 was any life whatever upon the earth. It is quite 

 another matter, however, to say that physico- 

 chemical categories exhausted the reality of Nature 

 in these pre-organic days. Indeed, if life and 

 mind and man have evolved from the reality 

 which was physically describable as a nebula, we 

 may safely say that the physical description is 

 certainly not exhaustive. 



In the same way, there were long ages, in the 

 evolution of organisms, during which (in addi- 



