INFLUENCE OF THE AGE OF THE PARENTS 23 



NORWEGIAN STATISTICS OF BIRTHS. 



Age of father 100 M : F E m 



Below 20 117.0 7.9 



20 to 25 101.5 0.7 



25 30 109.0 4.4 



30 35 105.9 2.9 



35 40 102.6 1.3 



40 45 104.6 2.2 



45 50 103.8 1.8 



50 55 98.4 0.8 



55 60 97.9 -1.0 



Over 60 99.8 0.1 



Rosenfeld gives a similar classification, arranged according to the age 

 of the mother, as follows : 



VIEXXA STATISTICS OF BIRTHS. 



Age of mother Male children Female children 100 M : F E m 



Below 17 19 7 271.4 46.1 



17 to 20 366 341 107.3 3.6 



20 25 4,444 4,161 106.8 3.3 



25 30 7,287 6,759 107.8 3.7 



30 40 9,907 9,356 105.9 2.8 



Over 40 1,412 1,396 101.1 0.5 



The enormous preponderance of male births in the case of mothers 

 under 17 years of age is probably the result of accident and not expressive 

 of a general law, the births, 26 in number, being too few to base a deter- 

 minate conclusion upon. If we combine all the mothers under 20 years 

 of age, the result will be : 



100 M :F = 110.6; E m =5.0 



The numbers now show a marked preponderance of male children 

 borne by very young mothers, which drops to the normal at the age of 

 20 and falls below it at the age of 40. 



It may be noted in this connection that the ratio of male and female 

 children is, in the general average, somewhat above the normal, possibly 

 indicating an imperfection of the record by not including all female chil- 

 dren. This, however, will not alter the conclusion. 



All these conclusions as regards the age of the parent seem to me to 

 lack a solid foundation, from the fact that the ages of the two parents 

 are not completely distinguished. I shall discuss this difficulty after 

 setting forth the results of the genealogical statistics collected by myself. 



The effect of difference of age between father and mother was investi- 

 gated by Sadler, who laid down the general law that the older parent has 



