Centesimal Scale (to nearest whole numbers).
| 150 fraternal couplets. | Random. | Observed. | Utmost possibilities. | Reduced to lower limit=0. | Reduced to upper limit=100. | ||||
| Centesimal scale. | |||||||||
| Fore-finger | 11·31 | 20 | 115 | 0 | 9 | 104 | 0° | 9° | 100° |
| Middle | 37·11 | 45 | 117 | 0 | 10 | 80 | 0° | 10° | 100° |
| Ring | 19·09 | 31 | 118 | 0 | 12 | 99 | 0° | 12° | 100° |
| Mean | 0° | 10° | 100° | ||||||
| 50 additional couplets, | |||||||||
| Middle finger only | 8·2 | 11 | 22 | 0 | 3 | 14 | 0° | 21° | 100° |
| Loops only, and on middle finger only. | |||||||||
| 150 couplets | 34·0 | 35 | 72 | 0 | 1 | 72 | 0° | 1¼° | 100° |
| 50 couplets | 6·4 | 7 | 14 | 0 | 0·6 | 8 | 0° | 8° | 100° |
Table XXIV. contains all the Observed events, and is to be read thus, beginning at the first entry. Pattern No. 1 occurs on the right fore-finger fifteen times among the A brothers, and twelve times among the B brothers; while in four of these cases both brothers have that same pattern.
Table XXV. compares the Random events with the Observed ones. Every case in which the calculated expectation is equal to or exceeds 0·05, is inserted in detail; the remaining group of petty cases are summed together and their totals entered in the bottom line. For fear of misapprehension or forgetfulness, one other example of the way in which the Randoms are calculated will be given here, taking for the purpose the first entry in Table XXIV. Thus, the number of all the different combinations of the 150 A with the 150 B individuals in the 150 couplets, is 150 × 150. Out of these, the number of double events in which pattern No. 1 would appear in the same combination, is 15 × 12 = 180. Therefore in 150 trials, the double event of pattern No. 1 would appear upon the average, on 180 divided by 150, or on 1·20 occasions. As a matter of fact, it appeared four times. These figures will be found in the first line of Table XXV.; the rest of its contents have been calculated in the same way.
Leaving aside the Randoms that exceed 0 but are less than 1, there are nineteen cases in which the Random may be compared with the Observed values; in all but two of these the Observed are the highest, and in these two the Random exceed the Observed by only trifling amounts, namely, 5·18 Random against 5·00 Observed; 1·87 Random against 1·00 Observed. It is impossible, therefore, to doubt from the steady way in which the Observed values overtop the Randoms, that there is a greater average likeness in the finger marks of two brothers, than in those of two persons taken at hazard.
Table XXVI. gives the results of applying the centesimal scale to the measurement of the average closeness of fraternal resemblance, in respect to finger prints, according to the method and under the reservations already explained in page 125. The average value thus assigned to it is a little more than 10°. The values obtained from the three fingers severally, from which that average was derived, are 9°, 10°, and 12°; they agree together better than might have been expected. The value obtained from a set of fifty additional couplets of the middle fingers only, of fraternals, is wider, being 21°. Its inclusion with the rest raises the average of all to between 10 and 11.
In the pre-eminently frequent event of loops with an outward slope on the middle finger, it is remarkable that the Random cases are nearly equal to the Observed ones; they are 34·08 to 35·00. It was to obtain some assurance that this equality was not due to statistical accident, that the additional set of fifty couplets were tabulated. They tell, however, the same tale, viz. 6·4 Randoms to 7·0 Observed. The loops on the fore-fingers confirm this, showing 5·18 Randoms to 5·00 Observed; those on the ring-finger have the same peculiarity, though in a slighter degree, 13 to 16: the average of other patterns shows a much greater difference than that. I am unable to account for this curious behaviour of the loops, which can hardly be due to statistical accident, in the face of so much concurrent evidence.
Twins.—The signs of heredity between brothers and sisters ought to be especially apparent between twins of the same sex, who are physiologically related in a peculiar degree and are sometimes extraordinarily alike. More rarely, they are remarkably dissimilar. The instances of only a moderate family resemblance between twins of the same sex are much less frequent than between ordinary brothers and sisters, or between twins of opposite sex. All this has been discussed in my Human Faculty. In order to test the truth of the expectation, I procured prints of the fore, middle, and ring-fingers of seventeen sets of twins, and compared them, with the results shown in Table XXVII.
Table XXVII.