28 ESSAYS OF A BIOLOGIST 



perhaps beg the question, to be proved I hope later, 

 as to whether the observed direction is progressive: 

 but I no longer beg the question of whether evolution 

 is a directional process. However we may argue on 

 the facts, the facts remain: and the facts are that 

 there has been an increase in certain qualities of or- 

 ganisms, both physical and mental, during geological 

 time. 



Meanwhile, let it be remembered, the simplest 

 forms have survived side by side with the more com- 

 plex, the less specialized with the more specialized. 

 Even Vv'hen we can trace a causal relation between 

 the rise of one group and the decay of another, as 

 with the mammals and birds on the one hand, and 

 the reptiles on the other, even then numbers of the 

 defeated group continue to exist. Thus, in broad 

 terms, evolution is not a transformation, be it pro- 

 gressive or no, of the whole of living matter, but of 

 a part of it. 



I will endeavour to sum up, in brief, what seem to 

 me the salient points of that process, a sketch of 

 which, inevitably hasty and inadequate, I have just 

 tried to give. 



During the time of life's existence on this planet, 

 there has been an increase, both in the average and 

 far more in the upper level, of certain attributes of 

 living things. 



In the first place there has been an increase in their 

 size, brought about by two methods, first by the in- 

 crease of size of the units of life themselves (cells, 



