16 THE FACTORS OF ORGANIC EVOLUTION. 



of muscles which are called into unusual action, to see that 

 over-straining of any one of the muscles of the giraffe s hind 

 quarters might quickly incapacitate the animal when putting 

 out all its powers to escape ; and to be a few yards behind 

 others would cause death. Hence if we are debarred from 

 assuming that co-operative parts vary together even when 

 adjacent and closely united if we are still more debarred 

 from assuming that with increased length of fore-legs or 

 /of neck, there will go an appropriate change in any one 

 / muscle or bone in the hind-quarters ; how entirely out of 

 ! the question it is to assume that there will simultaneously 

 take place the appropriate changes in all those many 

 components of the hind-quarters which severally require 

 re-adjustment. It is useless to reply that an increment of 

 length in the fore-legs or neck might be retained and 

 transmitted to posterity, waiting an appropriate variation 

 in a particular bone or muscle in the hind-quarters, which, 

 being made, would allow of a further increment. For 

 besides the fact that until this secondary variation occurred 

 the primary variation would be a disadvantage often fatal; 

 and besides the fact that before such an appropriate 

 secondary variation might be expected in the course of 

 generations to occur, the primary variation would have 

 died out ; there is the fact that the appropriate variation of 

 one bone or muscle in the hind-quarters would be useless 

 j without appropriate variations of all the rest some in 

 j this way and some in that a number of appropriate 

 variations which it is impossible to suppose. 



Nor is this all. Far more numerous appropriate varia 

 tions would be indirectly necessitated. The immense 

 change in the ratio of fore-quarters to hind-quarters would 

 make requisite a corresponding change of ratio in the 

 appliances carrying on the nutrition of the two. The 

 entire vascular system, arterial and veinous, would have to 

 undergo successive unbuildings and rebuildings to make its 

 channels everywhere adequate to the local requirements; 



