[Photo. Pictorial Agency]
Where two lines, beginning as parallels, curve to divide, a fresh line begins to appear between. Sometimes a single line forks into two or three. Again, triangular arrangements of lineations are seen on the zebra, and one can trace some of these back into lines running as a parallel series. Surely the causes which produce the ridges on a human or anthropoid finger cannot be quite the same biologically as lead to the formation of similar patterns in the skin of the zebra. There are mechanical or physical conditions, however, which condition the formation of ridges in a sandy shore, of powdery snow blown by the wind and tossed on a smooth frozen lake, as has already been noticed, and these conditions are being carefully elucidated by scientific observers. But why living tissues should produce patterns like those, just in those positions, and then reproduce them in living descendants with slight but important variations, is a totally different question, the answer to which must be reached in a different way.
While the ridges and furrows lie in parallels or curve in the same direction over some considerable surface of the sole and palm, they also gather up into more or less intricate, scroll-like patterns at various points besides those of the last joints of the fingers, which have chiefly engrossed popular attention hitherto. In man, the lemurs, lemuroids, and apes, these pattern points are numerous. In my own hands, there are on the left hand, besides the five finger-tip patterns, other five like them, and the right hand contains six. There are thus twenty-one complex patterns which might be used for identification.
On the other hand, when one reads of a mathematical attempt to compute the probabilities of two finger-prints being alike, it is not a question simply of comparing an unknown finger smudge with collections containing ten finger-prints each, for the unknown smudge may have been made, not from one of a possible set of ten finger-tip prints, but from one of those other local patterns not on the finger-tips at all. There is a saying often attributed to Huxley, who certainly used it wisely, that the value of grist from the mathematical mill depends on the quality of the corn put into the hopper. But official amateur mathematicians have made many much worse mistakes than the above in regard to probabilities in the realm of finger-print evidence.
In a few cases, especially in the feet patterns, often a very plain character, parallel or slightly wavy lines of no precise design, so to speak, may be found. A short time ago, when applying mustard to the feet of a lady in some kind of fit, I observed this almost featureless pattern in her toes. If such cases were as common in the hands as they are rare, the finger-print method would hardly be of any avail for identification. A teleologist of the old school of Paley might argue with some plausibility that the possible usefulness of those intricate patterns was the true meaning of their existence, otherwise not yet explainable. That the old Paleyan conception of nature having an end or purpose in view, the teleological explanation of things as useful to the being possessing them, had its own usefulness in giving a broader view of natural history facts in their interrelations, is borne out even by so great an authority as Charles Darwin himself. Are the markings in a bird’s eggs recognized by the sitting bird in those cases where the markings are peculiar—and some are like written characters—or are they purely accidental and useless? A correspondent in The Country-Side wrote a short time ago, describing a test case he observed of a thrush in his possession. This bird built a nest and laid therein five eggs, “varying in size from a good-sized pea to the normal size. The smaller ones I took away and substituted one from a wild bird’s nest; this the following day I found laid at the bottom of the aviary smashed. I again repeated the addition with the same result. I had carefully marked the eggs, so that there could be no mistake.” The writer signed himself “W. A., Wimbledon.”
Dr. Wallace’s view, as I understand it, is that variations in wild animals were due chiefly to immunity from enemies, allowing free play to the natural tendency to variation, kept only in check by its dangers, such as leading to betrayal by conspicuous colouring, and so on. Professor Poulton in The Colours of Animals, 2nd ed. p. 212, says:—
“It is very probable that the great variation in the colours and markings of birds’ eggs, which are laid close together in immense numbers, may possess this significance, enabling each bird to know its own eggs. I owe this suggestive interpretation to my friend, Mr. Francis Gotch: it is greatly to be hoped that experimental confirmation may be forthcoming. The suggestion could be easily tested by altering the position of the eggs and modifying their appearance by painting. Mr. Gotch’s hypothesis was formed after seeing a large number of eggs of the guillemot in their natural surroundings.”
Australian ewes know the bleat of their own lambs, however immense the flock, and all through nature we find this useful note of recognition. One of the most philosophic interpreters of living phenomena, viewing things from a very recent standpoint—Professor J. Arthur Thomson, in his fascinating Biology of the Seasons (p. 174), writing of the colour and texture of birds’ eggs, says:—
“In some cases, it is said, the shell registers hybridism—a very remarkable fact. It is another illustration of the great, though still vague, truth that the living creature is a unity through and through, specific even in the structure of the egg-shell within which it is developed. For although the shell is secreted by the walls of the oviduct, it seems to be in some measure controlled by the life of the giant-cell—the ovum—within.”