10 THE LAW OF BIRTHS AND DEATHS 



Any hypothesis put forward as an explanation of the 

 laws which regulate fertility should be a deduction from 

 the principles of organic evolution, since the degree of 

 fertility is one of the most potent factors governing the 

 survival and evolution of species. It is obvious that 

 there has been a steady decline of fertility from uni- 

 cellular organisms up to man, and we may, therefore, 

 ask ourselves : To what law, or laws, must the degree 

 of fertility have conformed in the past to produce the 

 results we see ? 



But to obtain by deduction a hypothesis which satis- 

 factorily covers all the facts is not an easy matter. For 

 if it be asserted that good feeding and improved sur- 

 roundings generally are conducive to high fertility, a 

 multitude of facts can be quoted in support of that view 

 and also against it. And if it be argued that hard con- 

 ditions are favourable to fertility, an equally imposing 

 body of facts can be quoted both for and against. The 

 evidence, indeed, seems to be a hopeless mass of contra- 

 dictions and inconsistencies. Yet I trust that the diffi- 

 culty has been successfully overcome in this work by 

 applying to fertility the principle of the vital optimum, 

 and distinguishing between fluctuations due to the several 

 factors : seasonal instincts, sexual fertility, asexual fer- 

 tility and ovulation. It has been the lumping together 

 in the past of the varying response of these several factors 

 to the same conditions which has been largely the cause 

 of the apparent confusion. When the governing abstract 

 principles are accurately stated, the evidence falls readily 

 into line. 



This is not a history of the birthrate problem, and it 

 has not been thought necessary to go at length into those 

 aspects of the problem already fully dealt with in other 

 works and worn threadbare by discussion. The non- 



