1912.] The Intensity of Natural Selection in Man. 471 



English Life-Tables. 



Period 



Males. 



Deaths per 1000 individuals. 



Females. 

 Deaths per 1000 individuals. 



— 1 years. 



1 — 5 years. 



— 1 years. 



1 — 5 years. 



1838—1854 



163 -50 

 158 -58 

 161 -04 

 171 -86 



134 -73 

 127 -58 

 104 -26 

 94-01 



134 -71 

 128 -73 

 131 -13 

 140 -66 



132 -60 

 124 -70 

 98 -55 

 89 -83 





1881—1890 



1891—1900 





Now, these data are the most considerable we can get and they involve all 

 environments in this country. If we might suppose the environment of the 

 country as a whole to have remained constant, we could only conclude that 

 it is certain that a high infant death-rate in a given community implies in 

 general a low death-rate in the next four years of life. 



It is difficult to realise how these data have come to be overlooked. It is 

 clear from them that the improved environment of the last 30 to 40 years 

 has not effected any improvement in the infantile death-rate. Either mother- 

 hood is less efficient, or the quality of the infants has degenerated, and they 

 can resist worse a better environment. It seems a priori unreasonable to 

 suppose the improvement in child mortality wholly due to an improved 

 environment which has produced no effect on infant mortality ; it is a priori 

 not unreasonable to assume that some of the improved child mortality is 

 due to increased infantile mortality. Can we to any extent determine these 

 proportions ? 



(2) There are two preliminary points to be considered in this matter. In 

 the first place the actuarial calculation of a life-table is not based on following 

 a given group of persons through life, and determining how many die at 

 each age. At first sight, therefore, our objection (a) above applies to 

 approaching the problem of natural selection in man from the life-table 

 standpoint. But a little consideration will show that it is far more justifi- 

 able than dealing with local districts in the same year. We have in the 

 first place an enormous mass of material — the whole country — and the 

 results are taken for 10 or 16 years. We thus obtain a stable community 

 representing the average of what is taking place in a community gradually 

 changing throughout the epoch. The general experience of actuaries who 

 use such tables for all purposes indicates that the death-rates calculated in 

 this manner for various groups of individuals closely represent what occurs, 

 if the same group be followed through life — the accidental excesses or defects, 

 scarlet fever or measles epidemics, etc., are averaged out when a whole 



