150 "Acquired Characters" 



ceased to operate. In illustration may be mentioned 

 the tanning of the skin during many years of life in 

 the tropics, the hardening of the skin under the 

 influence of prolonged pressure, the alteration of the 

 wall of the gull's stomach in consequence of a change 

 of diet, the enlargement of a muscle in the course of 

 exercise, the increase in the length and thickness of 

 the fur in a cold climate, the fattening of a prize 

 bullock or Strassburg goose, the acquisition of a 

 rapidly working coordination as the reward of much 

 practice. 



The problem known by the unhappy phrase "the 

 inheritance of acquired characters" may be stated 

 thus: Can a structural change in the body, induced 

 by some change in use or disuse, or by a change in 

 surrounding influences, affect the germ-cells in such 

 a specific or representative way that the offspring 

 will, through its inheritance, exhibit, even in a slight 

 degree, the modification which the parent acquired? 

 Evidence leading to an affirmative answer would 

 mean a retention of some form of the Lamarckian 

 theory of evolution. But if there is no convincing 

 evidence, then the raw materials of possible evolution 

 are restricted to germinal variations which arise more 

 or less spontaneously; endogenous, not exogenous; 

 "blastogenic," as Weismann said, not somatogenic; 

 outcomes rather than indents; expressions rather 

 than impressions. 



This is a question of far-reaching importance, and 

 our answer must affect not only our theory of evolu- 

 tion, but our conclusions in regard to the possibilities 



