Natural Selection 145 



specifically the characters thus acquired (89, 90). If 

 this opinion be correct, it is necessary to suppose that 

 characters acquired in the lifetime of an individual, 

 or recurring habitually through a sufficient number 

 of generations, can become so fixed in the race as 

 finally to be transmissible by heredity. The extreme 

 upholders of natural selection deny that such trans- 

 mission of acquired characters ever takes place, and 

 few, if any, undeniable proofs that it does have yet 

 been adduced. The darkening of the wing-patterns 

 of moths through the influence of cold during the 

 pupal stage has already been referred to, but the 

 offspring of these dark-hued insects require a repeti- 

 tion of the same conditions in order that they may 

 resemble their parents. It may be objected with 

 some reason that observation on a single generation 

 only is not sufficient to decide the point. That 

 acquired characters may in the course of several 

 generations become hereditary is what might have 

 been expected ; if this does occur, it must doubtless 

 contribute largely to the progress and evolution of 

 animal races. But until definite proof of its common 

 occurrence is forthcoming, it is wise to suspend judg- 

 ment on the subject. 



Closely connected with the action of the surround- 

 ings, and also depending for its efficiency in species- 

 making on the supposed inheritance of acquired 

 characters, is the influence of use and disuse (89). 

 This was suggested as a cause of evolution years 

 before the work of Darwin by the French naturalist, 

 Lamarck. Just as in the individual, those organs 

 which are most exercised become most highly de- 

 veloped, while those whose functions are neglected 

 become degenerate, so in the race it is believed that 

 various parts have become modified in response to 

 the activity or passivity of the animal. On this view 



K 



