Parental Age Effects on Man 25 



maternal age does not affect the mortality. Therefore, it 

 should be possible to use a group between the ages of 15 and 

 40 years as a basis of reference when the maternal age effects 

 have to be elucidated. The frequency of births in different 

 age groups cannot be determined directly because of the 

 fictitious nature of the population to be studied. Since only 

 cases of death are recorded, variations in death rate affect the 

 age structure of such a population. Furthermore, since the 

 material comprises data from individuals whose birth may be 

 several centuries apart it would not be possible to use data 

 given by vital statistics. The distribution of births varies in 

 different historical periods and for Finland the births grouped 

 according to the age of the mother are given only from 1871 

 onwards. The present author therefore thought that since the 

 mortality in the age group 20-29 years is probably not 

 affected by maternal age the percentage distribution of cases 

 of this age would reflect the frequency of births in the dif- 

 ferent maternal age groups. If similar percentage distribution 

 curves are constructed for ages at death below 6 years of age a 

 possible parental age effect would manifest itself in an excess 

 of cases in one of the maternal age groups, and this is what is 

 actually seen. Fig. 4 gives the distribution of cases in various 

 maternal age groups. As can be seen, the curves representing 

 deaths during the first and the second years of life have a dif- 

 ferent course from all the other groups studied. The maternal 

 age group of 25-29 years seems to be particularly favourable 

 for the infants whereas the maternal ages over 35 years seem 

 to have an excess mortality of infants less than 2 years of age. 

 If the distribution of cases is studied by the x^ method it 

 shows that the distribution of deaths of children under 2 

 years, from 2 to 19, and between 20 and 29 years, of these 

 maternal age groups, differs from a random distribution quite 

 significantly: x^ =25-7 (degrees of freedom = 6) P< 0-001. 

 If, however, deaths at 2-4 years are examined it may be noted 

 that the distribution of deaths in this age resembles more 

 closely the distribution of deaths in the 20-29 year group than 



