400 GREAT STEPS IN ORGANIC EVOLUTION 



of the organism, the ' heredity-germ ', and the animate en- 

 vironment. How slow we are to learn, for instance, Weis- 

 mann's lesson that the main steps of evolution are due to 

 changes emerging centrifugally from the germ-cell, not, so 

 far as we know, to changes impressed centripetally on the 

 body. Yet the germinal variations require the aid of somatic 

 functioning if they are to develop fully, and likewise the 

 aid of encouragement from the inorganic environment. Fur- 

 thermore the animate environment which forms part of the 

 selective sieve is also in process of evolution. It is a corre- 

 lated fourfold (' tetrakinetic ') evolution that we have to 

 deal with. 



But the crowning feature of evolution is the increased 

 masterfulness of behaviour. Even the very restricted brain 

 development of bony fishes belongs to a different epoch from 

 that of the medusae under whose umbrella they sometimes 

 shelter, and the otter is as far ahead of the fish as the fish 

 is ahead of the medusa. It is not merely intricacy of be- 

 haviour; it is not merely effectiveness; there is plenty of 

 both at very humble levels; the characteristic feature is 

 more freedom, plasticity, and resourcefulness. As we shall 

 afterwards see there is considerable reason for saying 

 though it is difficult exactly to prove it that the outstanding 

 fact about organic evolution is the increasing dominance of 

 Mind. As we think of the advance from invisible micro- 

 organisms to Mankind, we feel the grandeur of the process. 

 The apparently simple beginnings, dimly discerned, by us, 

 have had large issues, an extraordinarily fine, beautiful, 

 and interesting fauna and flora, an intricate self-regulating 

 and self-compensating system which has a moving equi- 

 librium in spite of the continual breaking-down of parts. 

 The eyes of Man's understanding have been darkened if 



