Finger Prints Part 14

Table x.x.xII. is derived from Table x.x.xI. by a process described by myself in many publications, more especially in _Natural Inheritance_, and will now be a.s.sumed as understood. Each of the six pairs of columns contain, side by side, the Observed and Calculated values of one of the six series, the data on which the calculations were made being also entered at the top. The calculated figures agree with the observed ones very respectably throughout, as can be judged even by those who are ignorant of the principles of the method. Let us take the value that 10 per cent of each of the six series falls short of, and 90 per cent exceed; they are entered in the line opposite 10; we find for the six pairs successively,

_Obs._: 55 48 064 059 050 074

_Calc._: 60 42 067 051 048 068

The correspondence between the more mediocre cases is much closer than these, and very much closer than between the extreme cases given in the table, namely, the values that 5 per cent fall short of, and 95 exceed.

These are of course less regular, the observed instances being very few; but even here the observations are found to agree respectably well with the proportions given by calculation, which is necessarily based upon the supposition of an infinite number of cases having been included in the series.

As the want of agreement between calculation and observation must be caused in part by the paucity of observations, it is worth while to make a larger group, by throwing the six series together, as in Table x.x.xIII., making a grand total of 965 observations. Their value is not so great as if they were observations taken from that number of different persons, still they are equivalent to a large increase of those already discussed.

The six series of observed values were made comparable on equal terms by first reducing them to a uniform PE and then by a.s.signing to M, the point of departure, the value of 0. The results are given in the last column but one, where the orderly run of the observed data is much more conspicuous than it was before. Though there is an obvious want of exact symmetry in the observed values, their general accord with those of the calculated values is very fair. It is quite close enough to establish the general proposition, that we are justified in the conception of a typical form of loop, different for the two thumbs; the departure from the typical form being usually small, sometimes rather greater, and rarely greater still.

I do not see my way to discuss the variations of the arches, because they possess no distinct points of reference. But their general appearance does not give the impression of cl.u.s.tering around a typical centre. They suggest the idea of a fountain-head, whose stream begins to broaden out from the first.

As regards other patterns, I have made many measurements altogether, but the specimens of each sort were comparatively few, except in whorled patterns. In all cases where I was able to form a well-founded opinion, the existence of a typical centre was indicated.

It would be tedious to enumerate the many different trials made for my own satisfaction, to gain a.s.surance that the variability of the several patterns is really of the quasi-normal kind just described. In the first trial I measured in various ways the dimensions of about 500 enlarged photographs of loops, and about as many of other patterns, and found that the measurements in each and every case formed a quasi-normal series. I do not care to submit these results, because they necessitate more explanation and a.n.a.lysis than the interest of the corrected results would perhaps justify, to eliminate from them the effect of variety of size of thumb, and some other uncertainties. Those measurements referred to some children, a few women, many youths, and a fair number of adults; and allowance has to be made for variability in stature in each of these cla.s.ses.

The proportions of a typical loop on the thumb are easily ascertained if we may a.s.sume that the most frequent values of its variable elements, taken separately, are the same as those that enter into the most frequent combination of the elements taken collectively. This would necessarily be true if the variability of each element separately, and that of the sum of them in combination, were all strictly normal, but as they are only quasi-normal, the a.s.sumption must be tested. I have done so by making the comparisons (_A_) and (_B_) shown in Table x.x.xIV., which come out correctly to within the first decimal place.

TABLE x.x.xIV.

+------------------------------------------------------+ Right Left Thumb. Thumb. ---------------------------------------- ------ ------ (_a_) Median of all the values of KL 125 101 (_b_) Median of all the values of NB 101 89 ------ ------ (_A_) Value of _a/b_ 124 111 (_A_) Median of all the fractions KL/NB 115 110 ======================================== ====== ====== (_c_) Median of all the values of AN 46 46 (_d_) Median of all the values of AH 44 33 ------ ------ (_B_) Value of _c/d_ 105 140 (_B_) Median of all the fractions AN/AH 108 136 +------------------------------------------------------+

It has been shown that the patterns are hereditary, and we have seen that they are uncorrelated with race or temperament or any other noticeable peculiarity, inasmuch as groups of very different cla.s.ses are alike in their finger marks. They cannot exercise the slightest influence on marriage selection, the very existence both of the ridges and of the patterns having been almost overlooked; they are too small to attract attention, or to be thought worthy of notice. We therefore possess a perfect instance of promiscuity in marriage, or, as it is now called, panmixia, in respect to these patterns. We might consequently have expected them to be hybridised. But that is not the case; they _refuse to blend_. Their cla.s.ses are as clearly separated as those of any of the genera of plants and animals. They keep pure and distinct, as if they had severally descended from a thorough-bred ancestry, each in respect to its own peculiar character.

As regards other forms of natural selection, we know that races are kept pure by the much more frequent destruction of those individuals who depart the more widely from the typical centre. But natural selection was shown to be inoperative in respect to individual varieties of patterns, and unable to exercise the slightest check upon their vagaries. Yet, for all that, the loops and other cla.s.ses of patterns are isolated from one another just as thoroughly and just in the same way as are the genera or species of plants and animals. There is no statistical difference between the form of the law of distribution of individual Loops about their respective typical centres, and that of the law by which, say, the Shrimps described in Mr. Weldon's recent memoirs (_Proc. Roy. Soc._, 1891 and 1892) are distributed about theirs. In both cases the distribution is in quasi-accordance with the theoretical law of Frequency of Error, this form of distribution being entirely caused in the patterns, by _internal_ conditions, and in no way by natural selection in the ordinary sense of that term.

It is impossible not to recognise the fact so clearly ill.u.s.trated by these patterns in the thumbs, that natural selection has no monopoly of influence in the construction of genera, but that it could be wholly dispensed with, the internal conditions acting by themselves being sufficient. When the internal conditions are in harmony with the external ones, as they appear to be in all long-established races, their joint effects will curb individual variability more tightly than either could do by itself. The normal character of the distribution about the typical centre will not be thereby interfered with. The probable divergence (= probable error) of an individual taken at random, will be lessened, and that is all.

Not only is it impossible to substantiate a claim for natural selection, that it is the sole agent in forming genera, but it seems, from the experience of artificial selection, that it is scarcely competent to do so by favouring mere _varieties_, in the sense in which I understand the term.

My contention is that it acts by favouring small _sports_. Mere varieties from a common typical centre blend freely in the offspring, and the offspring of every race whose _statistical_ characters are constant, necessarily tend, as I have often shown, to regress towards their common typical centre. Sports, on the other hand, do not blend freely; they are fresh typical centres or sub-species, which suddenly arise we do not yet know precisely through what uncommon concurrence of circ.u.mstance, and which observations show to be strongly transmissible by inheritance.

A mere variety can never establish a sticking-point in the forward course of evolution, but each new sport affords one. A substantial change of type is effected, as I conceive, by a succession of small changes of typical centre, each more or less stable, and each being in its turn favoured and established by natural selection, to the exclusion of its compet.i.tors. The distinction between a mere variety and a sport is real and fundamental. I argued this point in _Natural Inheritance_, but had then to draw my ill.u.s.trations from non-physiological experiences, no appropriate physiological ones being then at hand: this want is now excellently supplied by observations of the patterns on the digits.

THE END