SELECTION 455 



ception of the big fact that, after all, life has been sloivly 

 creeping upwards as the ages have come and gone. We 

 shall consider this fact later on, but meanwhile it is necessary 

 to be perfectly clear that being selected does not necessarily 

 confer on the creature any dignity or approval. It means 

 wholly and solely survivability in certain conditions, which 

 may be those of parasitism or sloth. The value of survival, 

 as judged by any human standard, depends altogether on the 

 conditions under which survival is secured. Survival may 

 be to a type that does not work for its living, but is an 

 unpaying boarder inside another creature, or to a mere drifter 

 in the stream of things, or to a rough egoistic combative type, 

 much less desirable, when judged by aesthetic or ethical 

 standards, than a gentle, altruistic, fine-brained type for 

 which the times were too stern. Survivability means little 

 in itself: one has to know the regional conditions and the 

 price paid. 



(5) It is important, for a second reason, to remember that 

 Natural Selection operates in great part with an external 

 reference to an established system of inter-relations which we 

 call the web of life. For it is this reference to an intricate 

 sieve that enables us to understand how minute and rather 

 subtle advances might have survival-value, or might turn the 

 scale between success and failure. A nuance — a shibboleth 

 — may be decisive. There are some kinds of fresh-water 

 mussel which cannot continue their kind without the un- 

 conscious co-operation of a particular species of fresh-water 

 fish. The parasite which causes the disease of liver-rot in 

 sheep cannot in Britain continue its race unless the free- 

 swimming larva find entrance to a particular species of 

 fresh-water snail Limncea truncatula, for other species do 

 not seem to serve. There are some flowers which cannot 



