66 THE PROBLEMS OF EVOLUTION 



minimum and disturbances result, such as rickets 

 in the growing child. Here again the body is in- 

 capable of adapting itself; its capacity for adjust- 

 ment is limited. 



The greater size of mountain plants produced by 

 MacDougal ^^ at the lower level of Tucson, the 

 development of a wider head in Daphnia by Wol- 

 tereck ^^ in response to overfeeding, and Sumner's 

 experiments with mice ^^ in which animals raised 

 at higher temperatures had larger feet, tails, and 

 ears, are distinct evidence that characters pro- 

 duced in individuals need not be adaptive, even 

 though associated directly with an environmental 

 stimulus. There is no reason to suppose that large 

 plants of a given species would succeed better as 

 individuals in the conditions prevailing at low 

 altitude than small ones; their increased size and 

 branching in MacDougal's experiments were appar- 

 ently an outcome of longer growing seasons and 

 better nourishment. Nor can one see how larger 

 feet and ears, and particularly longer tails, would 

 benefit mice in warm regions. Such characters 

 may be termed incidental individual responses in 

 contrast with the adaptive responses previously 

 considered, but they are no less definitely a result 

 of hereditary capacity expressed according to pre- 

 vailing environmental conditions. 



12 ^m. Nat, Vol. XLV, pp. 5-40, 1911. 



" Verh. d. Deutsch. ZooL Ges., pp. 110-172, 1909. 



" Jn. Exp. ZooL, Vol. VII, pp. 97-155, 1909. 



