Are Acquired Habits inherited? 28 



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sufficient to produce an observable variation; but that 

 where similar modifications are acquired in each of many 

 successive generations the cumulative effect becomes at 

 last observable in variation. Such cumulative effect is 

 obviously impossible in the case of the hen and her duck- 

 lings. And the case itself, it must be remembered, is only 

 adduced to illustrate the distinction between modification 

 and variation, and to make clear by a concrete example 

 the true nature of the question whether acquired modifica- 

 tions are hereditary. The transmissionist says that they 

 are hereditary, though perhaps in too slight degree to 

 be observable in the course of a single generation. Some 

 regard the evidence of such transmission as insufficient, 

 and others deny it altogether. 



Let us note in passing the important role that, in any 

 case, and quite apart from hereditary transmission, in- 

 dividual habit has to play. We start with an instinctive 

 activity. But the instinctive activity is the congenital 

 endowment of an organism which has also a certain range 

 of intelligence ; with the power of profiting by experience ; 

 with capacities for conscious adjustment to its environ- 

 ment ; with the ability to acquire new modes of activity 

 by modifying the old congenital types. The instinctive 

 activity tends to meet the normal conditions of the par- 

 ticular species; and under such normal conditions in- 

 dividual habit endorses, through repetition, the instinctive 

 activities, and tends to strengthen and firmly establish, 

 as an individual possession, that which was congenitally 

 given. Under abnormal conditions, however, intelligence 

 tends to modify the congenital activity so as to enable 

 it to meet the new requirements ; and then habit, through 

 constant repetition, tends to establish this modified type 

 of activity as an individual possession. In either case, 

 whether its tendency be conservative or adaptive, whether 



