8o THE POPULAR SCIENCE MONTHLY 



tremendous import. The much smaller proportion of women married 

 in the age classes 15 to 20 and 20 to 25 in England than in India 

 largely accounts for the difference between the birth rates in the two 

 countries. Third, in one way and another the birth rate is to an 

 increasing extent consciously controlled in every progressive country. 

 Fourth, early marriages and large families have become less consistent 

 with prudence. The expense necessary to rear children to the age of 

 self-support has become more burdensome. Besides, the rise of other 

 ambitions in life render both sexes more cautious about assuming the 

 marriage relation. No theory that leaves prudential considerations 

 out of the account can possibly explain the manner in which the social 

 and economic changes of recent years have influenced the birth rate. 

 Our conclusion, therefore, is that the diminishing birth rate is 

 primarily volitional, and that the various factors which make for 

 involuntary sterility are of minor importance.® 



It is of interest to note that so well known a biologist as Professor 

 H. "W. Conn, of Wesleyan University, subscribes to this conclusion. 

 He writes as follows : 



... I am very glad to give my opinion on this matter, recognizing that one 

 man's opinion on this subject is of no special value except as one vote. My own 

 opinion is that the primary reason for the diminishing birth rate is the vol- 

 \mtary one. The increasing demand for luxury raises the marriage age, and 

 the same desire, together with others kindred to it, lead to the intentional and 

 voluntary limiting the size of families. My own belief, judging from such 

 knowledge as would come to a single individual, is that this is the greatest 

 factor in the diminishing size of families. Indeed, I should rather be inclined 

 to believe that if this factor could be removed we should find the race practically 

 as fertile as in previous generations. 



*The frequency with which economists discuss the subject of population 

 as compared with biologists deserves a passing notice. Ever since the essay of 

 Malthus there have been few treatises upon economics without a chapter upon 

 the subject. Certainly, any text-book which failed to consider the matter to-day 

 would be regarded as incomplete. A century of criticism has established a fairly 

 consistent and satisfactory body of opinion. Moreover, the periodical literature 

 devoted to economics has in recent years been enriched by numerous articles 

 upon the diminishing birth rate. The American Economic and Sociological 

 Associations have now and then discussed the subject at their annual meetings. 

 On the other hand, there is a scarcity of literature from the biological stand- 

 point, I do not know of any place in print where a biologist has attempted to 

 advance a definite and complete theory of population, and in arriving at the 

 biological explanation of the diminishing birth rate I have been dependent upon 

 stray hints found here and there and especially upon information gained by 

 conversation with two of my colleagues, one a zoologist and the other a botanist. 

 There is no body of doctrine upon population to which biologists subscribe at 

 all comparable to that among economists. In other words, the weight of well- 

 defined opinion supports the view that the decline of the birth rate is volitional. 



