804 



AMEEIOAN MEN OF SCIENCE 



Table XV. Intervals in Years between' Marrla.ge and Birth of First Child and between Births 



OF Successive Children 



the average 3.2 j-ears after marriage, 

 whereas in a family of five or more the 

 interval is about a year and a half. In 

 the standardized family of two the second 

 child is born 4.2 years after the first, twice 

 as long as for large families. The delay 

 in the birth of children in small families 

 might be due to the same physiological or 

 pathological causes which make the family 

 small, but in most cases it is probably due 

 to voluntary' control. 



From Table XVI. it appears that 478 

 scientific men reported 716 sons and 668 

 daughters. This difference falls within 



Table XVI. Distribution op Sons an 

 Daughters 



Family of Parents 



Slbs Sisters Brothen 



126 

 256 

 456 

 500 

 615 

 426 

 336 

 248 

 144 

 70 

 55 



69 



123 



244 



266 



327 



235 



172 



121 



83 



34 



31 



57 

 1.33 

 212 

 234 

 288 I 

 191 

 164 

 127 j 



61 



36 I 



24 



Total 



1 

 2 

 3 

 4 

 5 

 6 

 7 

 8 

 9 



Total 



832 



81 



136 



130 



63 



41 



15 



5 



4 



3 



3232 



1705 



1527 



Family of SclentlOc Men 

 Children Sons Daughterf 



81 



272 



390 



252 



205 



90 



35 



32 



27 



42 



153 



199 



1.30 



104 



46 



16 



10 



16 



39 



119 



191 



122 



101 



44 



19 



22 



11 



478 



1384 



716 



668 



the limits of chance variation, and is not 

 likely to be significant. In the families 

 from which 832 scientific men come there 

 were 2,537 sons and 1,527 daughters re- 

 corded. This disparity may at first strike 

 the reader as inexplicable. Galton in his 

 "Hereditary Genius" says: "I also found 

 the (adult) families to consist on an aver- 

 age of not less than 2^ sons and 2| daugh- 

 ters each. Consequently each judge has 

 on an average of 14 brothers and 2^ sisters. 

 . . . 100 judges are supposed to have 150 

 brothers and 250 sisters." Nearly all 

 those whom I have questioned about this 

 statement think that it is correct. It 

 seems to most people obvious that if there 

 are equal numbers of boys and girls, a 

 boy must on the average have one more 

 sister than brother. However, a boy has as 

 many brothers as sisters, owing to the sex 

 composition of families. Thus in families 

 (^'if two, one fourth of the families will con- 

 j sist of two boys, one fourth of two girls 

 and one half of a boy and girl. On the 

 average, four boys will have among them 

 two brothers and two sister.s, and there 

 is a similar equality for large families. 



Table XVII. contains information in 

 regard to deaths in the families of scien- 

 tific men. For their brothers and sisters 

 tlie percentage of deaths recorded under 

 five 3'ears is 14.8, and under twenty-five 

 years it is 22.5. For their children the 

 percentages are 7.5 and 10.9. The death 

 rate has tlius decreased to half in a single 

 generation, and for the children of the 

 scientific men is probably the smallest 

 known. As only completed families are 



fc 



I 



