A. S. PARKES 
107 
106 
105 
104 
MALES PER 100 FEMALES 
103 
102 
1941 1851 1861 1871 1881 1891 1901| 19 | 1921| 1931 | 1941] 1951 | 
1850 1860 1870 1880 1890 1900 1906 1916 1926 1936 1946 1956-1960 
DECADE OR QUINQUENNIUM 
Fig. 1. Sex-ratio for live births in England and Wales, 1841-1960. 
The ratio, however, changes in another way. In years gone 
by, the excess of males at birth disappeared by the age of 5 years, 
because of the differential mortality of males over this period, 
and thereafter females were in excess. By the turn of the cen- 
tury, mortality had decreased and the ratio hovered about 
numerical equality between the sexes up to the age group 
15—-Ig years, and then owing to differential mortality and emi- 
gration the ratio fell sharply to below go males per 100 females 
in the 25-29 age group. At the present time, with the further 
decrease in child mortality, the excess of males found at birth 
is being preserved much longer, up to the age group 25-29 
years. 
The effect of differential mortality on the sex-ratio continues 
throughout the life cycle (Fig. 2). Thus, even now, females 
exceed males from the age group 35-39 onwards and the de- 
crease in the relative number of males becomes very sharp after 
age 55. It is in fact sharper at the present time than it was in 
92 
