28 ESSAYS OF A BIOLOGIST 



we have sketched in outline, and shall shortly proceed 

 to define more accurately. In so doing, I 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 organisms, 

 both physical and mental, during geological time. 



Meanwhile, let it be remembered, the simplest 

 forms have survived side by side with the more complex, 

 the less specialized with the more specialized. Even 

 when 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 progressive 

 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 



