Parental Age Effects on Man 31 



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DISCUSSION 



S acker: Aren't many of the early deaths at present due to con- 

 genital defects and could that be strongly related to parity ? 



Jalavisto: In young mothers the mortality rate increases according 

 to their parity, but in older mothers that does not matter so much. 



Sacher: So you do not think that parity is a major factor ? 



Jalavisto: It might be. 



Rockstein : There are two distinct ways in which parental age may 

 affect the offspring. There are the direct effects upon the foetus, 

 which might possibly be environmental, and there are those upon 

 the overall longevity of the successful offspring, which might be 

 hereditary. In the housefly, for example, the effect of the advanced 

 age of the parent upon the effective potential of the total population 

 is deleterious, primarily through fewer eggs, of lesser viability, 

 being produced by older parents. On the other hand, where we do 

 have surviving offspring, the longevity of the male housefly is 

 extended considerably (by about 20 per cent). We may likewise 

 have tw^o distinct effects in human populations : where an offspring 

 of an older parent survives, i.e. where an old mother successfully 

 produces young, the young will be longer-lived. The mother in this 

 way may be selecting (or producing a selective effect upon the 



