XV.] 



THE LAWS OF HABIT. 171 



The law that all habits tend to become hereditary is 

 subject to a very important limitation, of which I shall 

 have to speak when I come to treat of mind. 



When any peculiar tendency is inherited, it sometimes Inherited 

 appears in the offspring at the same age at which it appear 

 appeared in the parent, but sometimes earlier :i never, sometimes 

 probably, or only in the rarest cases, at a later age. Here- same age 

 ditary diseases afford many instances of both kinds of p^j^^^*|^'' 

 cases : of the peculiarity reappearing in the child, in some sometimes 

 cases at the same age at which it was acquired by the 

 parent, and in some cases at an earlier age. A remarkable 

 instance of the habit showing itself at an earlier age, is 

 the fact of young dogs, the parents of which have been 

 taught to point, themselves sometimes beginning to point 

 the first time they are taken out.^ I agree with Darwin 

 in attaching great importance to this class of facts, re- 

 specting the age at which variations occur, in throwing 

 light on the origin of species. 



There can be no doubt that even when a habit does not Hereditary 

 become hereditary, a tendency to it, or a facility for ac- wSiiout'^ 

 quiring it, does become hereditary. In those cases, for special 

 instance, in which a young pointer has not inherited the 

 habit of pointing, that habit is nevertheless more easily 

 acquired by Mm than it would be by a dog whose ances- 

 tors had not been taught to point. The case of a dog 



* Darwin on the Origin of Species, 4th ed. p. 14. (It is from the fourth 

 edition I shall always quote. ) 



2 The following is a very striking instance of the same kind : " Sir 

 C. Lyell mentions that some Englishmen, engaged in conducting the 

 operations of the Real del Monte Company in Mexico, carried out with 

 them some gi-eyhounds of the best breed to hunt the hares which abound 

 in that country. It was found that the gi-eyhounds could not support the 

 fatigues of a long chase in this attenuated atmosphere, and before they 

 could come up with their prey they lay down gasping for breath ; but 

 these same animals have produced whelps, which have grown up, and are 

 not in the least degree incommoded by the want of density in the air, but 

 run down the hares with as much ease as do the fleetest of their race in 

 this country." (Carpenter's Comparative Physiology, p. 987.) In this 

 case the power of breathing with facility in a rare atmosphere, which only 

 had a tendency to be produced in the parents, was congenital in the 

 oft'spring. 



