98 ON HEREDITY. 



.< 

 talents do not appear to depend upon the improvement of any 



special mental quality by continued practice, but they are the 

 expression, and to a certain extent the bye-product, of the human 

 mind, which is so highly developed in all directions. 



But if any one asks whether this high mental development, 

 acquired in the course of innumerable generations of men, is not 

 dependent upon the hereditary effects of use, I would remind him 

 - that human intelligence in general is the chief means and the 

 chief weapon which has served and still serves the human species 

 in the struggle for existence l . . Even in the present state of 

 civilization distorted as it is by numerous artificial encroachments 

 and unnatural conditions the degree of intelligence possessed by 

 the individual chiefly decides between destruction and life ; and 

 in a natural state, or still better in a state of low civilization, this 

 result is even more striking. 



Here again, therefore, we encounter the effects of natural selection, 

 and to this power we must attribute, at any rate, a great part of 

 the phenomena we have been discussing, and it cannot be shown 

 that in addition to its operation the transmission of characters 

 acquired by practice plays any part in nature. 



I only know of one class of changes in the organism which is 

 with difficulty explained by the supposition of changes in the 

 germ ; these are the modifications which appear as the direct 

 consequence of some alteration in the surroundings. But our 

 knowledge on this subject is still very defective, and we do not 

 know the facts with sufficient precision to enable us to pronounce 

 a final verdict as to the cause of such changes : and for this reason, 

 I do not propose to consider the subject in detail. 



These changes such, for example, as are produced by a strange 

 climate -have been always looked at under the supposition that 

 they are transmitted and intensified from generation to generation, 

 and for this reason the observations are not always sufficiently 

 precise. It is difficult to say whether the changed climate may 

 not have first changed the germ, and if this were the case the 

 accumulation of effects through the action of heredity would pre- 

 sent no difficulty. For instance, it is well known that increased 

 nourishment not only causes a plant to grow more luxuriantly, 

 but it alters the plant in some distinct way, and it would be 



1 Compare Darwin's ' Descent of Man.' 



