404 GREAT STEPS IN ORGANIC EVOLUTION 



dimorphism or divergence had many organic advantages; it became 

 also a liberator and educator of enriching emotions. 



A multitude of evolutionary steps must be summed up in the 

 phrase progressive differentiation and integration. Of unique im- 

 portance was the replacement of radial symmetry by bilateral sym- 

 metry which led on to head-brains and cephalisation, and was the 

 beginning of our knowing our right hand from our left. The 

 zoologist discerns that the word epoch-making is not too large for 

 such steps as the making of haemoglobin, the invention of blood, the 

 establishment of internal surfaces. The story of the evolution of 

 backboneless animals discloses a long succession of achievements. 



A step of great magnitude on the main line of evolution was the 

 origin of backboned animals, with a new type of central nervous 

 system opening up fresh possibilities of integration, registration, 

 and experiment. There was a conquering of new media — the dry 

 land and the air. There was a great extension of the range of 

 behaviour and a widening of resources. Economised reproduction 

 became possible as parental care lessened juvenile mortality. The 

 individual became more of an individual and counted for more in 

 life. Psychical linkages bound kin to kin. 



Finally, Man emerged, " the summit of the whole ". 



Looking back over the great spectacle of Animate Evolution, we 

 gather certain general impressions. There is progressive organisa- 

 tion of structural detail, increasing intricacy and correlation of func- 

 tions, a complexifying of the inter-relations of organisms, a grow- 

 ing masterfulness and resourcefulness of behaviour. 



The process of evolution from invisible Biococci to Mankind has 

 a magnificence which cannot be exaggerated. It has been a process 

 in which the time required has been of no consideration, in which 

 there has been neither rest nor haste, in which by-paths show as 

 much finish as the highways, in which broad foundations have 

 been laid so that the superstructure has been secure, in which, in 

 spite of the disappearance of masterpieces, there has been a con- 

 servation of big gains. It has had its outcome in personalities who 

 have discerned its magnificent sweep, who are seeking to understand 

 its factors, who are learning some of its lessons, who cannot cease 

 trying to interpret it. 



