Finger Prints

by Francis Galton

HEREDITY

Some of those who have written on finger marks affirm that they are transmissible by descent, others assert the direct contrary, but no inquiry hitherto appears to justify a definite conclusion.

[Chapter VIII.] shows a close correlation to exist between the patterns on the several fingers of the same person. Hence we are justified in assuming that the patterns are partly dependent on constitutional causes, in which case it would indeed be strange if the general law of heredity failed in this particular case.

After examining many prints, the frequency with which some peculiar pattern was found to characterise members of the same family convinced me of the reality of an hereditary tendency. The question was how to submit the belief to numerical tests; particular kinships had to be selected, and methods of discussion devised.

It must here be borne in mind that “Heredity” implies more than its original meaning of a relationship between parent and child. It includes that which connects children of the same parents, and which I have shown (Natural Inheritance) to be just twice as close in the case of stature as that which connects a child and either of its two parents. Moreover, the closeness of the fraternal and the filial relations are to a great extent interdependent, for in any population whose faculties remain statistically the same during successive generations, it has been shown that a simple algebraical equation must exist, that connects together the three elements of Filial Relation, Fraternal Relation, and Regression, by which a knowledge of any two of them determines the value of the third. So far as Regression may be treated as being constant in value, the Filial and the Fraternal relations become reciprocally connected. It is not possible briefly to give an adequate explanation of all this now, or to show how strictly observations were found to confirm the theory; this has been fully done in Natural Inheritance, and the conclusions will here be assumed.

The fraternal relation, besides disclosing more readily than other kinships the existence or non-existence of heredity, is at the same time more convenient, because it is easier to obtain examples of brothers and sisters alone, than with the addition of their father and mother. The resemblance between those who are twins is also an especially significant branch of the fraternal relationship. The word “fraternities” will be used to include the children of both sexes who are born of the same parents; it being impossible to name the familiar kinship in question either in English, French, Latin, or Greek, without circumlocution or using an incorrect word, thus affording a striking example of the way in which abstract thought outruns language, and its expression is hampered by the inadequacy of language. In this dilemma I prefer to fall upon the second horn, that of incorrectness of phraseology, subject to the foregoing explanation and definition.

The first preliminary experiments were made with the help of the Arch-Loop-Whorl classification, on the same principle as that already described and utilised in [Chapter VIII.]he following addition. Each of the two members of any couplet of fingers has a distinctive name—for instance, the couplet may consist of a finger and a thumb: or again, if it should consist of two fore-fingers, one will be a right fore-finger and the other a left one, but the two brothers in a couplet of brothers rank equally as such. The plan was therefore adopted of “ear-marking” the prints of the first of the two brothers that happened to come to hand, with an A, and that of the second brother with a B; and so reducing the questions to the shape:—How often does the pattern on the finger of a B brother agree with that on the corresponding finger of an A brother? How often would it occur between two persons who had no family likeness? How often would it correspond if the kinship between A and B were as close as it is possible to conceive? Or transposing the questions, and using the same words as in [Chapter VIII.], what is the relative frequency of (1) Random occurrences, (2) Observed occurrences, (3) Utmost possibilities? It was shown in that chapter how to find the value of (2) upon a centesimal scale in which “Randoms” ranked as 0° and “Utmost possibilities” as 100°.

The method there used of calculating the frequency of the “Random” events will be accepted without hesitation by all who are acquainted with the theory and the practice of problems of probability. Still, it is as well to occasionally submit calculation to test. The following example was sent to me for that purpose by a friend who, not being mathematically minded, had demurred somewhat to the possibility of utilising the calculated “Randoms.”

The prints of 101 (by mistake for 100) couplets of prints of the right fore-fingers of school children were taken by him from a large collection, the two members, A and B, being picked out at random and formed into a couplet. It was found that among the A children there were 22 arches, 50 loops, and 29 whorls, and among the B children 25, 34, and 42 respectively, as is shown by the italic numerals in the last column, and again in the bottom row of Table XX. The remainder of the table shows the number of times in which an arch, loop, or whorl of an A child was associated with an arch, loop, or whorl of a B child.