2.9. INDIVIDUALITY AN INTERLUDE.
I would like in a parenthetical section to expand and render rather more
concrete this idea of the species as one divaricating flow of blood, by
an appeal to its arithmetical aspect. I do not know if it has ever
occurred to the reader to compute the number of his living ancestors at
some definite date, at, let us say, the year one of the Christian era.
Everyone has two parents and four grandparents, most people have eight
great-grandparents, and if we ignore the possibility of intermarriage we
shall go on to a fresh power of two with every generation, thus:--
Column 1: Number of generations.
Column 2: Number of ancestors.
3 : 8
4 : 16
5 : 32
7 : 128
10 : 1,024
20 : 126,976
30 : 15,745,024
40 : 1,956,282,976
I do not know whether the average age of the parent at the birth of a
child under modern conditions can be determined from existing figures.
There is, I should think, a strong presumption that it has been a rising
age.
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