574 DISHARMONIES AND OTHER SHADOWS 



other considerations give us what we may call a scientifically 

 justified expectancy of discovering significance. But it is 

 through other paths of experience that men come to believe 

 if they have the will to believe in there being a strategy 

 behind evolution, which is partly what believing in God 

 means. Given, in other than scientific experiences, some con- 

 viction of an increasing purpose, ultimately spiritual in con- 

 tent, the question rises whether the state of affairs in Ani- 

 mate Nature and the way in which this has come about is 

 congruent with a religious interpretation. 



We repeat that a scientific survey of the system of which 

 we form a part cannot prove anything as to the significance 

 of the whole ; that is certainly not its metier; yet it is legiti- 

 mate to ask whether the impressions afforded by the scientific 

 survey are consistent with regarding Nature as the expression 

 of a Divine Thought or Purpose. But it is often said that 

 this consistency can be recognised only by those who are will- 

 ing to ignore the seamy side of things. Let us therefore 

 face some of the disharmonies and shadows. 



2. Extinction of Highly Specialised Types. 



One of the shadows which cannot be ignored is the lack 

 of plasticity in highly specialised types. The physical world 

 is changeful, in climate, in weather, in surface-relief, and 

 there are many living creatures which are unable to change 

 with it. They have gone too far to tack, and they perish. 

 Adaptations to novel conditions abound, but the over-special- 

 ised are sometimes victims of their own perfection. Many 

 types of great excellence have thus passed away without leav- 

 ing any direct descendants. The graceful Graptolites, the 

 robust Trilobites, the highly specialised Eurypterids, the 

 great Labyrinthodonts, Ichthyosaurs, Plesiosaurs, and the 



