354   Life and Letters of Francis Galton

struggle for existence, and that it is of interest to know what these subtypes are. The colour of animals is often found to be intimately correlated with their power or incapacity to thrive under certain conditions, and it may well be the same in the case of man. Galton cites Baxter' to prove that in America, where the pressure of life peculiar to modern civilisation is even greater than with us, the black-haired persons are less liable to nearly every form of disease than the fair-haired. He observes, however, that it is needful at the same time to determine the relative fertility of the light and dark haired, and that it would be very important to distinguish between the children of a dark-haired man who had sprung from a light-haired stirp, and those of a similar man from a dark-haired stirp. The schedule is fairly straightforward and contains the first statement of Galton's system of numerals for relationship, i.e. child 1, parents 2, 3, grandparents 4, 5, 6, 7, etc., the even numbers standing for males and the odd for females (No. 1 excepted, which may have either sex) ; the number of any individual when doubled gives that of his father, and his mother's number is obtained by the addition of one to the number of his father'. The characteristic Galtonian statement is made incidentally that

"The inquiry will have the merit of being accompanied by incidental pleasures; it will be an excuse for corresponding with distant friends and relations on topics of common interest, and it is probable that not a few facts of family history much prized by its members will in many

cases be incidentally brought to light by its means."

Galton himself was so interested in family history that he quite naively overlooked the fact that nine-tenths of humanity either fear to examine it or are frankly bored by it. Against that dead-weight of inertia Galton could effect little, and there is no evidence that these circulars were ever returned in sufficiently adequate numbers to serve as a basis for an answer to his inquiry.

' Medical and Anthropological Statistics of the Provost-Marshal-General's Bureau, Washington, 1875.

2 Galton published a letter on this numerical system of relationship in Nature, Sept. 6, 1883, under the title : "Arithmetic Notation of Kinship." Taking f = father of, m = mother of, he gives the following equivalent systems of notation

Literal System.   Child

r f

-r

i   

ff

fff   I mff f -f etc.

Binary System.   1

   i   

10   11

r   7

100   101

1

In

mf   mm

1   r-   1   r   -1

mmf ffin   mfm fm m   mmm etc.

110   111

1000   1001 1010   1011   1100   1101 1110   1111

etc:   etc.

The Binary System is cumbersome but simple, we add a zero for the father and a unit for the mother of any individual to that individual's number. The decimal system is as follows: