Factors Influencing the Human Sex-ratio. 127 

 72 (i447) 



Some factors influencing the human sex-ratio. 



By C. C. Little (by invitation). 



[From the Carnegie Institution of Washington, 

 Cold Spring Harbor, N. Y.] 



In 1908 R. and M. De W. Pearl 1 published data derived from 

 the vital statistics of the city of Buenos Ayres, concerning the 

 sex ratio in the following types of matings: (1) Italian X Italian, 

 (2) Spanish X Spanish, (3) Argentine X Argentine, (4) Italian cT 

 X Argentine 9 , (5) Spanish c? X Argentine 9 . 



Of these crosses it will be noted that three are not racial crosses 

 and two are. The data obtained by the Pearls stretched over a 

 period of ten years. Although including very large numbers 

 their data has certain minor disadvantages, for the most part 

 frankly recognized by the authors themselves. First in im- 

 portance is the fact that their data do not take still births into 

 consideration, and second, the Argentine race may properly be 

 considered as itself somewhat of a mixture and therefore less 

 likely to breed as a pure race. If however the first three crosses 

 be recorded as pure racial matings and the last two as racial 

 hybrids, the ratio of males to 100 females in the two types may be 

 compared as follows: 



Table I. 





Total Cases. 





9 9- 



Ratio. 



Difference. 



Diff. 

 P. E. 



Pure matings 



Hybrid matings .... 



187,925 

 3L59I 



94.993 

 16,255 



92,932 

 15,336 



102.21 ±.l6 "1 

 IO5.99 ±.39 / 



3-78±-42 



9.0 



It will be noted that there is a significant excess of males in 

 the hybrids. The Pearls note this fact and state in addition that 

 environmental differences also fail to account for the results. 

 They further agree that experimental investigations are neces- 

 sary in order to reach adequate explanations for the observed 

 facts. 



1 Biol. Bull., 15, 194-205. 



