humanfaculty4 - page 234 of 305

Inquiries into Human Faculty

—namely, 200. Then the number of such children in the A and B classes

respectively, being in the proportion of 82 to 5.4, will be 115 and 85.

We have next to determine the average lengths of the A and B

generations, which may be roughly done by basing it on the usual estimate

of an average generation, irrespectively of sex, at a third of a century, or

say of an average female generation at 31. 5 years. We will further take 20

years as being 45 years earlier than the average time of marriage, and 29

years as 4.5 years later than it, so that the length of each generation of the

A group will be 27 years, and that of the B group will be 36 years. All

these suppositions appear to be perfectly fair and reasonable, while it may

easily be shown that any other suppositions within the bounds of

probability would lead to results of the same general order.

The least common multiple of 27 and 36 is 108, at the end of which

term of years A will have been multiplied four times over by the factor

and B three times over by the factor 0.85. The results are given in the

following Table :—

The general result is that the group B gradually disappears, and the group

A more than supplants it. Hence if the races best fitted to occupy the land

are encouraged to marry early, they will breed down the others in a - very

few generations.

Number of Female Descendants who themselves become Mothers

Of 100 Mothers whose Marriages

and those of their Daughters all

take place at, the Age of 20 Years

Of 100 Mothers whose

Marriages and those of their

Daughters all take place at the

Age of 29 Years

(Ratio of increase in each

successive Generation being 1.15)

(Ratio of Decrease in each

successive Generation being