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Hereditary Genius
355
son. The dotted line indicates the period of life before the age of 22;
the double line, the period between 22 and the average time at which
his son is born; the dark line is the remainder of his life.
On the other hand, a man of the race N, which does not contribute
more than 2.5 generations to a century, that is to say, 40 years to a
single generation, does not attain the age of 22 until (on the average
of many cases) 7 years after his father's death; for the father was 40
years old when his son was born, and died at the age of 55 when the
son was only 15 years old. In other words, during each period of
18+15+7, or 40 years, men of mature life of the race N are alive for
only 18+15, or 33 of them; hence the total mature life of the race N
may be expressed by the fraction 33/40.
It follows that the relative population due to the races of M and N,
is as 33/27 to 33/40, or as 40 to 27¹, which is very nearly as 5 to 3.
1
A little consideration of the diagram will show that the proportion in question, will
invariably be in the inverse ratio of the intervals between the two generations, which in
the present case are 27 and 40 years.
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