96 ORGANIC EVOLtTTION — THE FACTORS 



hearing in another, agility in a third, and so forth ; bat 

 every normal deer (and abnormality is rare among wild 

 animals), as regards every other quality, varies a little — 

 not much — above or below a certain mean. If the fittest 

 survive, and we know that on the whole they do survive, 

 it is surely clear, that those animals who in the aggre- 

 gate of their essential qualities rise above the specific 

 mean, will be those that continue the race ; and since 

 among the offspring there will be some who in the 

 aggregate of their qualities surpass their parents, the 

 continued survival of the fittest will in time result in 

 evolution as regards all the other qualities. 



The fundamental error is the same as that which he 

 fell into when discussing the spurs of the Chaja screamer, 

 and which Mr. Cunninghame fell into when discussing 

 the horns of deer — the tacit assumption that evolution, 

 if due to the accumulation of inborn variations, must 

 proceed on lines of abnormal variations. Thus he writes 

 in the passage under discussion — "But now suppose 

 that one member of a herd — perhaps because of more 

 efficient teeth, perhaps by great muscularity of stomach, 

 perhaps by secretion of more appropriate gastric juices 

 — is enabled to eat and digest a not uncommon plant 

 which the others refuse. This peculiarity may, if food is 

 scarce, conduce to better self-maintenance, and better 

 fostering of the young if the individual is a hind." But 

 is it necessary to entertain such a very improbable sup- 

 position? A deer which suddenly varies in such a 

 manner as to be able to eat and digest a plant which 

 the rest of its species refuse to eat and cannot digest, 

 would be as abnormal as a mammal " with two little 

 excrescences on its frontal bones as an occasional vari- 

 ation," or a bird " much given to fight," " on the wings 

 of which thickenings of the skin occurred," " symmetri- 

 cally," " at the points required," which " on their first 

 appearance were decided enough to give appreciable 



