HUMAN FECUNDITY 105 



12. In conclusion, some calculations may be conveniently 

 added to illustrate the strength of human fecundity, which, as we 

 shall see, is constantly underestimated. Let us consider a popu- 

 lation of a million born in the same year, half of whom are males 

 and half females. Let us suppose that they all marry, each couple 

 before the age of twenty producing two children, half of whom 

 are girls and half boys. For the sake of simplicity we may imagine 

 that at the end of each twenty-year period the parents die simul- 

 taneously with the birth of their offspring. Then, if the children 

 marry and produce offspring as did their parents, we shall have 

 a standard population of 1,000,000, which will neither increase nor 

 decrease so long as these conditions are fulfilled. If, however, the 

 average number of children is 2|- per couple, then in 100 years the 

 population will be 3,050,000; if three, 7,954,000; if four, 

 32,000,000 ; if five, 97,650,000. 



