REMOVAL OF INHERITED TENDENCIES. 437 



conclusion appears to be sustained by ordinary observation, although 

 the conditions which bring about the reappearance of abnormities may 

 be quite different from those which tend to restore lost normalities. 

 The more attentively, however, the subject is considered, the more 

 apparent does it become that the differences in the two cases are far 

 greater than has been supposed, extending back to the antecedents, to 

 the nature, duration, and outcome of the process. 



One of the constants of reproduction is more or less variability in 

 the offspring, and this may be healthy or physiological, or it may be 

 morbid. When of the former, it is in no way incompatible with life, 

 and may prove permanent to the blood ; but more commonly it is sup- 

 planted by older characters, which may have disappeared for one or 

 more generations. The nature of the prepotent tendency to reversion 

 seems to be grounded upon a single antecedent, that of prolonged 

 'transmission. As a rule, it happens that the longer this has occurred 

 the more deeply fixed does any character become, and hence the more 

 likely, when caused to vanish by modifying conditions, to reappear 

 through reproduction. 



Exceptionally, it is true, modifying circumstances seem to have 

 so ripened in the organism for a variation that a change of structure 

 and function is uninterruptedly transmitted. 



That the prolonged existence of characteristics should tend to fix 

 them strongly upon the blood is in entire harmony with familiar expe- 

 rience. For example, there is nothing permanent in the minute diver- 

 sities among the individuals of a race, but the general type has long 

 existed, and is preserved for generation after generation with unbroken 

 fidelity. No competent observers think it possible to raise the intel- 

 lectual grasp of a stupid family or race to the highest average by the 

 culture of one or two generations. Time and continuity of influence 

 are indispensable to the fixing and maintenance of intellectual excel- 

 lence. To the influence of these elementary conditions is no doubt 

 due the wide disparity between the transmission of instinctive and in- 

 tellectual skill. In the latter process the thoughts and actions are so 

 numerous and diversified, that the continuance of any one is necessa- 

 rily short and evanescent, while in the former they are few and always 

 in the same narrow channel. In this way the instinctive brain-impres- 

 sions of the animal are grooved or deeply stamped into its structure, 

 making their acts a necessary resultant ; while those of intelligence 

 leave but a shallow impress, so that skillful execution can only be at- 

 tained by individual training and practice. 



When the variation that springs from the ripe influence of modify- 

 ing conditions is of a normal character, it has no inherent quality which 

 renders indefinite perpetuation impossible. Let its favoring condi- 

 tions be continuously applied, and it may become permanent to the 

 blood, and thus acquire the prepotency of reversion. Quite otherwise 

 is the result with variations of an abnormal or morbid character. 



