The American Midland Naturalist 
PUBLISHED BI-MONTHLY BY THE UNIVERSITY 
OF NOTRE DAME, NOTRE DAME, INDIANA 
VOL. VIII. JANUARY, 1923. NO 7: 
Evidences of a Differential Death Rate of the Sexes Among Animals. 
S. W. GEISER, PH. D., 
Washington University, Saint Louis. 
(From the Zoological Laboratory of the Johns Hopkins 
University.* ) 
I.—INTRODUCTION. 
It has long been known by actuaries and statisticians that 
in the human species the death-rate of males is greater than 
that of females. This is true not only for deaths occurring 
after birth, but also for prenatal deaths. 
Long before the time of DARWIN (1871). attention had been 
called to the fact that males greatly outnumbered females in 
stillbirths. An overwhelming mass of statistical data gives 
evidence of this phenomenon. Thus, (to cite some older and 
some newer work) it may be noted that for the decade 1865- 
1875 in the various countries of Europe, where reliable sta- 
tistics are to be had on this point, the proportionate numbers 
of male stillbirths to female ‘stillbirths was very high. In 
France, during this decade, the index-number for males was 
144 (as compared with 100 for females) while in Italy, Bel- 
gium, Sweden, and Prussia, the index numbers were 140, 135, 
133, and 129, respectively. In 1895 the index-number for 
males in Berlin was 137; in Hamburg, in 1896, it was 125. In 
fine, all available data on this point evidence this relation in 
the proportionate death-rates of the sexes before birth. It 
would appear rather clearly indicated that the unborn male 
human infant is less viable than the female. a 
The post-natal mortality of the males, also, is higher than 
*With hearty acknowledgments to Professor S. O. MAST, for direetion, criticism, 
and help. 
