32 Discussion 



population) to the extent that she is herself a long-lived individual. 

 That is, she may be still fertile at the age of 40 or 45 and producing 

 a large family. These offspring will then be long-lived by virtue of 

 this and the net effect will be not to have an adverse effect upon the 

 successful offspring. In other cases, offspring from older parents will 

 be stillborn or malformed at birth. However, Sonneborn has 

 analysed the statistics for a large population of offspring from the 

 New York City vital statistics records. He found that there was a 

 stronger correlation, in a positive sense, between 'paternal age and the 

 number of stillbirths, than with maternal age. This is usually 

 ignored in the statistics, because normally the age of the mother is 

 known rather than the age of the father. 



Berg: Was the normal lifespan about 45 years in 1800 ? 



Jalavisto: Yes. 



Berg: That would be before the onset of diseases of senescence. 

 Causes of death were chiefly physical or infectious in nature. 



Danielli: There are three distinct factors which might affect the 

 mortality of the children. First, there may be changes in the Mendel- 

 ian characteristics transmitted through the chromosome material. 

 If it were true that there were no parental effects, one would think 

 that no type of deterioration of the chromosome genes was contri- 

 buting to your results. Prof. Jalavisto. Second, there is the possi- 

 bility that you may get cytoplasmic inheritance effects coming in. 

 Then, of course, the actual environment to which the embryo is 

 exposed is also changing as the age of the mother changes, but not as 

 the age of the father changes. So the mother has two chances (or 

 three, if cytoplasmic inheritance effects are included) of altering the 

 expectation of life of the child, whereas the father has only one 

 chance. 



Maynard Smith: Even in organisms without placentae, e.g. 

 Drosophila, there is plenty of evidence that the age of the female 

 laying an egg will influence the probability that this egg will hatch. 

 In human data one might suppose that the age of the mother, through 

 the cytoplasm of the egg she produces, influences the rate of still- 

 births. There is no difficulty in supposing that either egg cytoplasm 

 or uterine environment might influence the survival during the first 

 two years of life, but they are less likely to influence long-term 

 survival. 



Danielli: To what extent are more children surviving in recent 

 years from older mothers than was the case 100 years ago ? If more 

 are indeed surviving, the shift to the right of the final curve in Dr. 

 Benjamin's death curves might be due to such an effect. 



Comfort : There are several social factors which affect the parental 



