300 DR MATTHEWS DUNCAN ON THE 



their earlier pregnancies. That the latter is to be accepted to the exclusion of the 

 former supposition is evident, if we observe that the married life of the women 

 with families above 10 is not long enough to admit of their having gone through 

 the series of lengths of pregnancies given in the Table opposite each successive 

 child. It is thus shown, — 



3. That wives bearing more than 10 children, or wives bearing very large 

 families, breed more rapidly than others during their whole child-bearing lives. 



Wives, therefore, who bear numerous progeny, do so in virtue of two differences 

 from other married women. They bear their children more rapidly, and they 

 continue fertile longer than their neighbours. 



Were the third conclusion just given not before us, it might be supposed that 

 the rapid bearing of earlier children was a result of youth and vigour. This 

 supposition is not only inconsistent with the third conclusion, but with the law 

 to be hereafter demonstrated, that the oldest women, who are continuedly fertile, 

 bear children more rapidly than any other. 



The average length of interval between all successive children is (1 09;, nearly 

 20 months. 



I have frequently heard it said, that a fertile woman bears a child every 2 

 years. Some authors have made careful statements on this point. Whitehead* 

 says, that fertile women produce children every 20 months ; but " this in- 

 cludes abortions, false conceptions, so-called premature deliveries, and all having 

 an unsuccessful issue, the average amount of which will be rather more than one- 

 and-a-half for each individual." Sir William Petty long ago laid it down, that 

 " every teeming woman can bear a child once in 2 years." Malthusj adopts 

 the same period, and refers to the Statistical Account of Scotland as confirming 

 it. The number and exactness, however, of the data here adduced, and the cir- 

 cumstance that they include only children born alive (excluding still-born and 

 abortions), leave no room for doubt that all the authors referred to under- estimate 

 the rate at which married women bring children into the world.} 



On this point Sadler is so full and distinct that I quote his words. " The 

 interval of time," says he, " at which the fruitful couples produce their children, 

 calculated from the period of their marriage to the birth of their last child, in- 

 cluding the greater prolificness of the first year, exceeds 2 years. It extends to 

 between 2^ and 2^ years, if calculated from the first birth. "$ In this calcula- 

 tion, as in that of the interval between marriage and the birth of a first child, 

 Sadler evidently errs, making the former too long, and the latter too short. 

 For both he gives no data ; yet, in regard to the interval between the births of 



* On Abortion and Sterility, p. 245. 



f An Essay on the Principle of Population, vol. ii. p. 3. 



+ See also Roberton's Essays and Notes on the Physiology and Diseases of Women, p. 185 



§ Vol. ii. p. 30. 



