160 EVOLUTION, OLD AND NEW. 



be transmitted with certainty so as to eventuate in 

 national characteristics. * It is a pleasure to find that 

 here, too, habit is assigned as the main cause which 

 underlies heredity. 



Modification will be much prompter with animals. 

 When compelled to abandon their native land, they 

 undergo such rapid and profound modification, that at 

 first sight they can hardly be recognized as the same 

 race, and cannot be detected in their disguise till after 

 the most careful inspection, and on grounds of analogy 

 only. Domestication will produce still more surprising 

 results; the stigmata of their captivity, the marks of 

 their chains, can be seen upon all those animals which 

 man has enslaved; the older and more confirmed the 

 servitude, the deeper will be its scars, until at length it 

 will be found impossible to rehabilitate the creature 

 and restore to it its lost attributes. 



"Temperature of climate, quality of food, and the 

 ills of slavery here are the three main causes of the 

 alteration and degeneration of animals. The conse- 

 quences of each of these should be particularly con- 

 sidered, so that by examining Nature as she is to-day we 

 may thus perceive what she was in her original con- 

 dition." t 



I have more than once admitted that there is a 

 wide difference between this opinion, which assigns 

 modification to the direct influence of climate, food, and 

 other changed conditions of life, and that of Dr. Erasmus 

 Darwin, which assigns only an indirect effect to these, 

 while the direct effect is given to changed actions in 

 Tom. xiv. p. 316, 1766, f Ibid. p. 317. 



