Physiological and Psychological Heredity. 273 



understand. But why not view psychological heredity in the same 

 way ? Apart from prejudice, routine, and preconceived ideas, 

 which will not give way, the reason is that, rightly enough, people 

 find the idea of generation, as applied to the soul, unintelligible. 

 But all becomes plain if we connect psychological heredity, as 

 effect, with physiological heredity, as cause. 



We see, then, that this relation of causality between the two 

 heredities is only a particular case of the relations of physical and 

 moral. Its only peculiarity is, that here psychical heredity corre- 

 sponds with permanent tendencies, not only in the individual, but 

 also in the race, the family. Further, whereas physiological 

 heredity is immediate, psychological heredity is indirect, mediate. 

 The organism is transmitted directly; and if, together with the 

 organism, the nervous diathesis of the parents is transmitted, their 

 mental aptitudes are likewise transmitted by this intermediary. 



It will, perhaps, be asked, seeing that we assert a perfect corre- 

 spondence between nervous and psychical phenomena, why we 

 consider mental heredity as an effect of physiological heredity. 

 Might we not reverse the proposition ? 



We have already combated that thesis. But, independently of 

 the negative reasons given, there is one which seems to us positive. 

 It is, that experience shows mental development to be always and 

 everywhere subject to organic conditions, while it does not show 

 the converse to be true in a general way. 



If there is any order of phenomena that is unequivocally worthy 

 of being called psychological, it is the facts of consciousness. But 

 consciousness presupposes for its production definite organic con- 

 ditions. If they do not exist, there is no consciousness ; and 

 when they disappear, consciousness is at an end. And it may be 

 remarked, that as regards the brain, consciousness does not stand 

 in any vague, general relations. Though physiologists still debate 

 as to whether the important point in the brain, considered as a 

 psychological organ, is its weight, or its chemical constitution, or 

 the number of its convolutions, or its form, or its type, it is likely 

 that each of these conditions possesses a special importance of its 

 own. Thus, it may be affirmed that an adult human brain weigh- 

 ing less than two pounds induces that mental state which we call 

 idiocy. 



