250 
GENETICS: C. C. LITTLE 
Proc. N. a. S, 
oscillation as a whole would be but an incident in a series of climatic and 
oceanic changes which began with the opening of the Glacial period. 
1 Goldthwait, J. W., Amer. J. Set., 32, 1911 (293). 
2 Twenhofel, W. H., Ibid., 28 ,1909 (147); 30, 1910 (66, 69). 
3 Mayor, A. G., These Proceedings, 3, 1917 (523). 
4 Andrews, K. C, New South Wales Handbook, Brit. Assoc. Adv. Sci., 1914 (525, 532). 
5 Siissmilch, C. A., Introduction to the Geology of New South Wales, Sydney, 1911 (154). 
6 Cadell, H. M., Trans. Edinburgh Geol. Soc, 7, 1897 (179). 
7 Brogger, W. C, Norges geol. Unders., No. 31, 1901 (713), and No. 41, 1905. 
A NOTE ON THE HUMAN SEX RATIO 
By C. C. Little 
Carnegie Institution of Washington, Cold Spring Harbor, L. I., N. Y. 
Communicated by R. Pearl, March 20, 1920 
From data collected at the Sloane Maternity Hospital in New York City, 
it has recently been shown ^ that there is a significantly higher male 
sex ratio at birth among progeny whose parent are not of similar nationality. 
This result confirmed a paper published by the Pearls^ in 1908, based on 
data derived from vital statistics of the City of Buenos Ayres, and had in 
addition a decreased source of error due to improved methods of recording 
the data and the inclusion of still births as well as living births in the cal- 
culations. 
During the past year, a further study of the same records has been 
made concerning the sex ratio among the progeny of certain other types 
of matings and a preliminary attempt at analysis made by contrasting the 
sex ratios of the offspring of primipara with those of subsequent births. 
Table 1 shows the sex ratios of five categories of matings: European 
"pure," European "hybrid," United States white, British West Indies 
colored, and United States colored. European pure are matings in which 
both parents were of the same nationality. European hybrids are off- 
spring whose parents are of different nationality. United States white 
include a random sample of parents coming from various parts of the 
United States but preponderantly from the East and especially from 
New York State and New York City. British West Indies colored, are 
offspring from colored parents born in the British West Indies, and United 
States colored are offspring from colored parents born anywhere in the 
United States. 
In each case the probable error of the ratio obtained has been calculated 
for the numbers observed. On the basis of these probable errors, the differ- 
ences between the various ratios can be fairly compared with respect to 
their probable significance. 
As has before been shown, there is a significant difference between the 
European "pure" and the European "hybrid" and between the former 
