ORGANIC EVOLUTION — PHYSICAL 13 



as regards both qualities ; and though there is reason, 

 as we shall presently see, to conclude that on the whole 

 the offspring are usually inferior to the parents, never- 

 theless, since they are generally numerous, and the 

 process of selection almost always severe, the survivors 

 in each generation, as a rule, surpass their parents in 

 the sum of their qualities ; and as a result, there is 

 usually evolution as regards the whole race even when 

 the essential qualities are many. Moreover, we have 

 assumed for the sake of simplicity that each ancestor 

 was pre-eminent in one quality only, but of course, as 

 constantly happens in nature, a single individual may 

 approach pre-eminence in several or many qualities, or 

 conversely, may fall below the specific mean in several 

 or many qualities : in the latter case he tends of course 

 to be eliminated, and to leave no offspring, and there- 

 fore to have no influence on the future of the race ; but 

 in the former he tends, even more than if he were 

 eminent in one quality only, to survive and to leave 

 offspring who, inheriting his characteristics, tend as a 

 result to survive in greater numbers than the off- 

 spring of the less happily endowed, and therefore to 

 render concurrent evolution in several directions more 

 rapid. 



Lastly, the statement that artificial selection differs 

 from natural selection in that but a few qualities are 

 developed by it, is true in a very limited sense only ; 

 for instance, by causing the evolution of the greyhound 

 man has necessarily caused the evolution of a great 

 number of subsidiary qualities, each subserved by a 

 number, in some cases by an immense number, of finely 

 co-ordinated structures. Therefore though speed alone 

 has been aimed at, yet to obtain it evolution in many 

 directions has been necessary (e. g. in " wind," " limb," 

 circulatory and nervous systems, &c.). On this score 

 then there is no essential difference between artificial 



