K VOLUTION OF THE COLORS OF BIRDS. 45 



about this result. This might very easily be explained, 

 indeed, by the effects of inherited use and disuse. " If 

 the effects of use and disuse of parts are inheritable," 

 says Mr. Spencer, "then any change in the fore parts 

 of the giraffe which affects the action of the hind limbs 

 and back will simultaneously cause, by the greater or 

 less exercise of it, a remoulding of each component in 

 the hind limbs and back in a way adapted to the new 

 demands; and generation after generation the entire 

 structure of the hind quarters will be progressively fitted 

 to the changed structure of the fore quarters, all the ap- 

 pliances for nutrition and innervation being at the same 

 time progressively fitted to both." But the factors of 

 use and disuse aside, we must assume that all of these 

 complex changes occurred simultaneously. It might be 

 contended that slight variations in one direction which 

 were advantageous might take place in one generation, 

 and the correlative changes in other parts at some future 

 time. In reply to this Mr. Spencer says: " 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 inight be expected in the course of 

 generations to occur, the primary variations would have 

 died out; there is the fact that the appropriate variation 

 of one bone or muscle in the hind quarters would be 

 useless without appropriate variations in all the rest — 

 some in this way and some in that — a number of appro- 

 priate variations which it is impossible to suppose." 



Mr. Ball either cannot or will i:iot see the force of 

 Spencer's objections. He says: "All that is needed is 

 that natural selection should preserve the tallest giraffe 

 through times of famine by their being able to reach 

 otherwise inaccessible stores of foliage. The continual 

 variability of all parts of the higher animals gives scope 



