TEE STUDY OF NATURAL SELECTION 131 



constant) the survivors of an infantile population subjected to environ- 

 mental conditions making for a high death rate should in later years 

 show a lower mortality than the survivors of a population subjected to 

 less stringent conditions of life. 



The Possible Selective Element in Infant Mortality. — That the 

 preservation of the weaker children may result in a population of adults 

 below the maximum physical fitness is an idea as old as the study of 

 Spartan history. The wide acceptance of the Darwinian theory and 

 the modern reduction in the death rate — accomplished largely by the 

 saving in the early months of life — have combined to give it consid- 

 erable prominence in recent years. 



To solve the problem one must find a series of districts 9 differing 

 as much as possible in the mortality of the early months of life, and 

 determine whether those which have a lower mortality in infancy have 

 a higher proportion of men unfit for military service or a higher adult 

 mortality. 



Such attempts have been made, for instance, by Eahts, Kruse, 

 Gruber, Koeppe, Prinzing, Elben and others. The indeterminateness 

 of these studies is apparent not only from the discordant conclusions 

 but also from the obvious inadequacy of the statistical technique. 10 



To Yule 11 and Snow 12 belongs the credit of having first applied 

 the modern statistics to this problem. Yule's data and methods, 

 however valuable they may be from the standpoint of the relationships 

 between the mortality of early and later life in a series of districts, 

 seem quite inadequate to the solution of the problem of the selective 

 or non-selective nature of infantile mortality. 13 



A first great merit of Snow's laborious study is that he fully recog- 

 nizes the multiplicity of disturbing factors and has attempted in as 



• Snow (see below) is quite right in insisting that the question as to what 

 proportion of the general death rate is selective should be answered on national 

 mortality statistics. From the point of view of evolution, or of sociology, such 

 data are of far more value than the more complete records which can be secured 

 in individual pedigrees, for to be of evolutionary or of national social importance 

 the intensity of the selective death rate must be measured on a perfectly general 

 population. 



10 Examples are given in subsequent footnotes. 



" G. U. Yule, ' ' On the Possible Selective Influence of Mortality in Infancy 

 on Mortality in the Next Four Years of Life," Supplement to the Eeport of 

 the Medical Officer of the Local Government Board (Great Britain), 1910, 

 Cd. 5,263. 



12 E. C. Snow, ' ' The Intensity of Natural Selection in Man, ' ' Drapers ' Co. 

 Res. Mem. (Univ. Coll., Lond.), Stud. Nat. Det. 7, p. 43, London, Dulan & Co., 

 1911. 



13 This is clear from the criticisms brought forward by Snow. Practically 

 as much has been admitted elsewhere; see Jour. Boy. Stat. Soc, 75: 133-135. 

 In his study Yule shows a caution in interpretation of results which is not aa 

 evident in the main body of the medical officer's report. 



