150 Heredity. 



1. There must be first of all a perfect correspondence between 

 the physical and mental constitution of the parents. A moment's 

 reflection will show that each of these two general states the 

 physical and the mental constitution is itself the result of many 

 particular states, which, taken together, impress on every individual 

 that distinct and special mark which is in physiology called 

 temperament, in psychology, character. 



2. But even if these first conditions are fulfilled, there is some- 

 thing more required. It is not enough that the physical and 

 mental constitution of both parents should be equipoised in a 

 general sense ; there are, moreover, particular conditions of age 

 and health, which are indispensable. Disproportion in the ages of 

 the two parents, where it does not produce sterility, gives the 

 preponderance to the younger. Experiments made by Girou de 

 Buzareingues on various animals show that the progeny of an old 

 male and a young female are less like their father, in proportion as 

 he is feeble and the mother vigorous, and that the progeny of an 

 old female and a young male resemble the mother less in propor- 

 tion as he is vigorous. Nor is the influence of the actual state of 

 health, of vigour, or of cheerfulness in one of the parents less 

 marked in the progeny. 



3. Finally, there are sundry other states more accidental and 

 transitory than those named, which influence the act of generation. 

 Positive facts show that these states, all transitory as they are, 

 exert a very powerful influence on the progeny, and ensure the 

 preponderance of one or the other sex. We need only recall the 

 fact that nothing is more common than the intellectual feebleness 

 of children begotten in a state of intoxication ; that a popular 

 tradition, adopted by several authors, and to some extent supported 

 by history, represents illegitimate children as cleverer, more hand- 

 some, and more healthy than others, because they are 'love- 

 children.' On the other hand, 'when parents,' says Burdach, 'have 

 a dislike to one another, they beget ugly forms, and their children 

 are less lively and vigorous.' 



It is easy to see that there are many circumstances of this kind 

 which must influence the act of generation. When we consider 

 how impossible it is to have these general, particular and for- 

 tuitous conditions in perfect equilibrium in the two parents, we 



