Can Two Identical Ridge Patterns Actually Occur
--Either On Different Persons Or On The Same Person
(Reprint from Finger Print Magazine November, 1945)
In the April, 1942, issue of this Magazine there was published an opinion by the Honorable Tom Beauchamp, Judge of the Texas Court of Criminal Appeals, which was handed down on April 19, 1941, in the matter of Newton Grice vs. The State of Texas. This was on an appeal from his conviction the year previous, largely on finger print evidence.
After an exhaustive review of finger print cases in the State of Texas and other jurisdictions, the Judge made the startling and timely proposal, that in the light of present day knowledge and experience, those who hold that there CAN BE two identical finger patterns �should assume the burden of proving their position.� His Honor is to be commended for his courage in raising the issue in a judicial decision rather than �off the record.� In this suggested shifting of the burden of proof, he recognizes the passing of the former controlling assumption of a possible duplication of ridge patterns, and also registers his disagreement with such an assumption, although on other than biological grounds.
Premise 50 Years Old
It should be remembered that the assumption of possible pattern duplication accompanied the birth of the use of finger prints as a means of individual identification over 50 years ago. At that time the whole idea and method was new, and not so much was known about the biological factors involved in the formation of the ridge patterns in the embryo as is known today. So, as a precautionary measure, the possibility and probability of a ridge pattern being duplicated simultaneously in different digits of the same person or in different persons was investigated. To be an absolutely certain means of bodily identification, a finger pattern had to be exclusively individual to the body possessing it. Even a remotely possible duplication would be fatal to the exclusiveness necessary for accurate identification.
The laws of chance were called upon to help �prove� that there could be no duplication. But the application of ratios, favorably weighted to prove exclusiveness, only �proved� that there was one chance in many billions of prints. Because this chance, according to the figures, was supposedly so remote, it was interpreted as being the equivalent of �never.� But in spite of this interpretation and the astronomical figures involved, there still remained the chance of duplication at some time. The occurrence of the chance duplication is not so remote as it may first appear, for it may occur at any time during the period proscribed by the terminal figures. It does not have to be the first nor the last of the series but may occur at any time within the limits set by the terminal figures. Fifty years ago �today� was �remote� if we regard the millions of people who have since been born. According to some of the figures then cited this present day generation would appear to be somewhere in the middle of the figures, with plenty of time for a duplication to occur, if it can occur. But, no advocate of this reasoning has had the thoughtfulness to tell us when the count began!
Judicial Belief Prevails
The net result of this line of reasoning had to be an admission of a possible duplication which might occur at any time. This admission was at variance with the purpose of the investigation, and also at variance with an intuitive belief that there could be no duplication. Hence, the interpretation �never� placed upon the results of the numerical calculations. The textbook admission of a possible duplication has continued to co--exist, but with diminishing force, along side of the intuitive belief that duplication is impossible. This latter belief has controlled our judicial procedures in spite of the calculated chance of a duplication. The sincere endeavor to solve a biological problem by mathematics has resulted in a confusing and anomalous situation.
Either Nature can produce duplicate patterns or she cannot. That during the past 50 years of critical use and study no duplicate patterns have been discovered is not the exact equivalent of saying that they cannot occur, but it points strongly in that direction. It is hardly conceivable that among the many millions of prints compared, at least one case of exact repetition should not have been discovered, if duplication is possible.
In the light of this half century of critical use is it not more realistic to reason that a duplication cannot occur as that it can occur? That is, I take it, what Judge Beauchamp proposed when he suggested shifting the burden of proof. Biological research in recent years is practically unanimous in its conclusion that there can be no duplication. This being so, why cannot an effort be made to work out a non--mathematical formula or line of reasoning, in layman's language, and using known biological facts, to confirm the faith that is in us?
In an Oklahoma decision the Court in Stacy vs. State, says:
�In conformity to decisions of the courts in many states, we take judicial knowledge that there are no two sets of finger prints exactly alike.�
This statement I interpret as meaning that there are no two flesh patterns which are identical. The phrase �exactly alike� seems to be intended as meaning �identical,� and the term �finger prints� as the equivalent of the flesh pattern from which contact impressions are made. It is well known that no two imprints from the same digit can be identical any more than two signatures written by the same hand can be identical, but for different reasons. It is common knowledge that Nature never has been known to make any exact duplicates--�no two snow--flakes, no two grains of sand, no two leaves, no two of anything are exactly alike, that is, identical down to the most minute detail of form or size or position or combinations of them. Variations are always found in one more of these factors which are distinctive enough and sufficiently extensive to establish the necessary perceptible differences required to distinguish one object from another in the same category of general likenesses. We are dealing with an assembly of anatomical units each of which is a four--way variable in itself.
The school of thought which holds the belief that Nature cannot duplicate exactly, even if she so desired or had sufficient cause to do so, cites her supreme effort as exemplified by the so--called duplicate twins, considered to be the result of the division of a single fertilized egg. With all of the advantages of identical hereditary environment associated with a single egg, the duplication consists of sex only, either males or females. Extensive studies of duplicate twins of both sexes demonstrates that duplication (beyond sex) is not a totality, but is confined to close approximations, some of which are pictorial and some structural. Such features as general build, height, body bulk, color of hair, skin or eyes, mannerisms, etc., in varying combinations are the rule, but no exact duplications of all the pictorial and structural features in one twin are found in the other. In fact, like--correspondences are often found in comparing unrelated persons.
The further and more minutely an examination is carried the greater become the number and character of the differences. In other words �likeness� is pictorial as well as structural. The alignment of the structural factors is the foundation for the pictorial presentation of those factors. In finger prints the pictures are in the form of whorls, loops and arches. Nowhere else on the human body are there found so many anatomical structural factors grouped together in such a small area which are available for the purpose of bodily identification as in the ridged skin of our hands and feet.
Nature Always Varies
It is a fundamental principle that the more minute the characters relied upon, the greater becomes their individualizing power. This is because of four concomitant attributes, namely, the form of the feature, its size, its position actual and relative, and its sequence in any series of anatomical characteristics. All of these four factors must agree simultaneously in any two flesh configurations or patterns as to each of several hundred anatomical units (sweat glands and their respective pores) or there is no duplication. It is also held that duplication is impossible because of the inherent variability of controlling growth factors during fetal development. Even Nature cannot duplicate them as she has no �master mold� into which all human life can be poured. Each creation represents a master �blue print,� but exhibits all of the variables inherent in individual workmanship.
Let us survey this complex and rather confusing (to the layman) situation, and try to identify and tabulate only a few of the more obvious variables that are involved in the formation of these anatomical mosaics, which we know as ridge patterns. With a fairly good picture of these elements we can the better calculate what must happen during the growth of these structural elements in the formative months of fetal life, if identical configurations are to occur. With these observations as a foundation we can then draw our own conclusions as to the possibility of duplications occurring at any time.
A Finger Print Described
For the purpose of this study we shall think of a finger print as an anatomical record, made by bodily contact, from and of the ridged skin configuration on the terminal phalange of a digit. We should keep in mind the difference between the mechanically made record and its fleshy matrix of origin. Viewed from the mechanical or printing standpoint there are two kinds of impressions: (1) the most common, and the one usually meant when we use the term �finger print,� is registered by the summits or crests of the ridges, which are broad enough to usually record many sweat pores, but may not if the ink or other recording medium is too abundant; (2) the second kind, more or less rare, is made in terms of the furrows and registers as fine lines which show no pore openings. Imprints from the ridge crests are comparable with those from the face of type as in using a rubber desk stamp. Records from the furrows are comparable with an imprint from an engraved plate or die, �intaglio� as the printers say. Unless otherwise noted ridge prints will be assumed.
Finger Print Characteristics
Reasonably clear and extensive impressions from the ridged surfaces are accepted in practice as a substantial substitute for the ridged design itself, just as we accept and use impressions from a rubber desk stamp to convey a specific message. This acceptance becomes so much a matter of routine to the professional identifier that one must be constantly on guard on becoming careless in the interpretation of a print, which is always something less than a perfect reproduction of the ridge details. To this extent it parallels the imprint from a desk stamp. As to each there must be enough recorded to convey the correct message.
Unlike desk stamps whose printing surface is smooth and all in one plane, a finger print is recorded from a relatively soft cylindrical flesh matrix which gives under pressure to conform momentarily with the plane of the printing surface, but returns to normal form immediately [when] the pressure is removed. Instead of presenting a smooth printing surface the crests of the ridges are microscopically uneven and the deeper parts may not be printed unless the maximum pressure is exerted. The ridged surface approximates 180 degrees of the digital cylinder which extends from the phalange articulation to the apex of the pad (pattern core area). From the core point the ridged skin curves sharply until it meets the nail at the tip of the digit. This part may be likened to one--half of a cone. So, a finger print registers the pattern on the cylinder portion and about half of its conical terminal. How much of this conical portion is recorded depends upon pressure, the softness or firmness of the flesh, and the skill of the operator.
Because of this topographical variation and the variable printing pressures upon the soft and elastic flesh pad it is impossible to make absolutely identical prints from the same flesh matrix. The operator cannot register in his mind the precise degree of pressure, nor the number of degrees through which the cylindrical digit is rolled. Also the exact degree of softness of the flesh of the finger bulb, which may vary according to the subject's health, cannot be mentally recorded, and so the pressure cannot be repeated with accuracy. The foregoing has assumed that the same operator takes a series of prints. If another operator prints the subject then his ignorance of the pressure and the degree of rolling previously used, defeat his ability to make identical imprints. Because of certain accepted rules for printing there will be approximations but no exact or identical duplicates.
Identical impressions are not necessary nor are they called for in making an identification. What is necessary is a record extensive enough and clear enough to convey the true message such a finger print is capable of delivering. The technical question is: �Is the questioned imprint from identically the same body or digit as the known standard?� The primary subject of identification is the human body. The means used for identifying it is a contact record from an available part of that body. The records cannot be identical, but the body must be.
A ridged skin imprint being a body--contact record requires the presence of the body from which it is made at the scene of a crime where chance impressions have been found, or in the place where official records are made. The body may be alertly alive, in a comatose condition, or actually dead, but it must be present in whole or in part.
Other kinds of body--contact records include casts of the jaw such as a dentist makes, or of the foot or the many varieties of moulage casts such as death masks. Portrait photographs are also anatomical records but are not body--contact records. They are made by the action of reflected light on a light--sensitive emulsion, and may vary greatly according to the lens used, the angle of the light, the quality of the light and the chemical treatment of the exposed emulsion. Each kind of record has its place in the identification process.
Because the ridged skin pattern is exclusively individual and bodily contact is necessary to make the record, we are able, through inference, to use a chance imprint found at the scene of a crime as convincing evidence of the bodily presence of the suspect, who perhaps was not seen by anyone near the place of the crime, but was apprehended at a later time and place. A finger print or any other ridged skin record is thus seen to be an evidential fact, or more accurately a series or sequence of related evidential facts of embryonic origin, permanently a part of our body, and not acquired subsequent to birth.
What Are These Evidential
Why are these anatomical facts so convincing when added together in series? In the description of a finger print the phrase �anatomical record� was used. What is the nature of this record? What does it register that is so important in identification? Superficially it registers the pictorial design of the ridged skin in terms of the ridge crests. In clearly made records the ridges are seen to be studded with minute white dots aligned along the ridge axis or near to it. These dots upon close examination are seen to register the sweat pores, which are the external or surface openings of the sweat glands situated deep in the true skin. For every visible pore there is an invisible gland imbedded in the flesh of the digit, and therefore permanently fixed in its actual position, as well as in its relative position to each and every other of the 100 (more or less) glands in the finger bulb or pad. So, from an evidential standpoint, a finger print registers the number of glands imbedded in the skin in terms of their pores or surface terminals. It also registers their precise spatial position and relationship to one another. It also registers the precise and relative positions of the pore terminals on the surface, as well as combinations of them such as forks, eyelets, etc. These are evidential facts or circumstances which took shape and became fixed for life early in the embryo development. The number of glands or �basic units� is determined by counting their pore terminals. The pore with its surrounding ring of epidermis is called a �ridge unit.� A single isolated unit is called an �island.�
Without magnification, each pore in a print appears much like any of the others, a white dot on a dark field. But with adequate magnification they are revealed to be erratically variable as to their form, size, position and sequence. These attributes are supremely critical factors because all four of them must be simultaneously identical (not merely alike) as to each and every anatomical fact or circumstance in an alleged duplicate pattern or configuration. These four factors are applicable not only to the minute pores but also to the pattern as a whole or any part of it, also to any other part of the ridged skin on palm or sole.
Two Obvious Groups
It is obvious to every technician that these anatomical facts may be grouped into two visual categories, (1) the large or macroscopic pattern features needing little or no magnification for their analysis, (2) the minute microscopic features needing magnification for their analysis. To the macroscopic category belong the patterns as a whole, including the deltas and pictorial contours. The microscopic category consists almost wholly of the pores externally situated and the glands which require dissection for their examination.
In general, pattern forms vary within rather definite limits. Galton first defined and named these forms arches, loops and whorls, each form possessing exclusive characteristics separating it from the other two. Each category became a �Class.� The definitive characteristic for the whorl class is the presence of at least two triangular deltas or furrow plots; for the loop class it is the presence of but one delta, and for the arch class it is the absence of any delta, although a vestige may be present.
More detailed studies by Galton of the whorl class revealed stable variations in the direction and relationships of the typelines or radiants. These relationships he used to separate the two--delta class of patterns into nine subclasses which he graded as �Genera.� Further studies by myself disclose that each Genus can be subdivided into Species and Subspecies. Working backward from Galton's genera I found stable characteristics which could be used to subdivide these forms into Families and Orders. So we have a consecutive series of form variations which can be graded under the same divisional names or categories that zoologists and botanists use for grading animals and plants. In their regular sequence these grades are: Class, Order, Family, Genus, Species and Subspecies. The varieties under subspecies are so variable that further sub classing is very difficult if not impracticable.
After determining the pattern subspecies and its size, the next step is usually the consideration of the ridge details such as forks, eyelets, islands, etc., noting their form, size, position and sequence. These characteristics comprise the microscopic group and for demonstration purposes require photographic enlargement. If the situation requires the comparison of the form, size, position and sequence of the pores (ridge units) then adequate magnification plus enlargement becomes necessary.
The process of making an identification consists of establishing a consecutive series or sequence of related anatomical facts, any one of which might be found in any other series or association, but all of which in sequence can conceivably coexist in but a single pattern only; in other words spell but one anatomical name.
As an illustration of sequence variation take the alphabetical letter sequence A--M--R--Y. In their alphabetical order they spell no present English word, but each letter character has its exclusive individuality as does a ridge unit or pore. Now, arrange the letters in the sequence MARY, or the series ARMY, or the series MYRA, and instantly we have a related series of alphabetical circumstances any one of which may be found in other sequences but when taken together as a related series spells but one name. The significance of sequence is intensified when we consider the thousands of words made by varying the number and the sequence of but a few of the 26 letters of our alphabet, or of the ten Arabic numerals.
Unlimited Ridge Formations
Carry over the idea of sequence into the anatomical field of ridge patterns and the result is the same, but with this difference, that the basic units and the ridge units are not limited in number to 26 static forms, but are practically unlimited as to their form, size, position and sequence. Their combinations are also unlimited so that there is no necessity in nature for exact duplication of details. Duplication would require Nature to repeat in microscopic detail a related series of ridge units, each of which is a four--way variable by itself! If this is possible then there must be simultaneous and identical agreement in two separate embryos or in two digits of the same fetus of at least the following 13 variables:
1. The Shape (Topography) and--
2. The Size of the fetal finger bulb down to the smallest dimension.
3. The Form or pattern alignment of the hundreds of sub--surface sweat glands must be identical in both areas.
4. The several hundred ridge units on the surface must fuse together so as to create ridges, forks and other ridge characteristics of identically the same number of units.
5. The pattern contours of homologous ridges and their length must be identical in both areas.
6. The Form, and--
7. The Position of homologous ridge unit groups such as forks, eyelets, islands, etc., must be identical.
8. The angle of forking and--
9. The direction of forking must be identical.
10. The Form, and--
11. The Size of homologous pores, and--
12. The Position of the pores, relative to the ridge axis, and--
13. To each other, must be identical.
Pattern Types Vary, Too
In addition to the foregoing microscopic details past studies have shown that the general pattern forms fall naturally into an orderly gradation of pattern types beginning with the parent 2--delta whorl and degenerating through several well defined stages ending with the delta less arch, as illustrated in the �Finger Print Family Tree.� The whorl degenerates into composite forms which are divisible into several subspecies. Then, through the degeneration of one of its deltas the composite becomes a one delta transitional or neuter loop possessing a distinct vestige of the lost delta. This Neuter Loop looses its vestigial delta and becomes a Pure Loop with but one delta. The Pure Loop modifies into a transitional form known as the �Tented Arch� in which the distal radiant, standing erect, becomes the axis or �tent pole.� Nature then eliminates this distinguishing feature leaving not even the vestige of a pattern, the whole configuration consisting of transverse ridges, slightly arched in the center or core area, known as the Pure Arch. For duplicate ridge patterns to occur, each of these gradations must be identical for its respective type level. In other words the two patterns must conform to the zoological formula of:
8. Size. In addition to these
form variations the size of the two patterns must be identical.
So, adding together these interdependent and individually variable attributes we find that there are 21 of them, each one associated with each of the other 20 variables. It is necessary that each variable be identical with a homologous variable in two separate areas!
Bringing all of these threads together at a focal point and applying the �Rule of Reason,� is the duplication of such a required series of genetic variables conceivable? To repeat, Nature has no master mold into which all human life can be pored and from which she can turn out exact duplicates. Obviously, she does work from a master blue print, and therefore the results exhibit all of the variability inherent in individual workmanship. Nature's supreme effort to duplicate through the splitting of a single fertilized egg results only in the duplication of sex. Even the bilateralism of our external body is usually far from exact when critically examined. It seems to have as its limits many very close pictorial and structural correspondences which constantly fall short of being identical. By--and--large the pictorial and structural ensemble is close enough for artistic and practical purposes.
Because of the mental and mechanical variables involved in the recording process, identical finger impressions are impossible; and because of a multitude of genetic growth variables in the fetus identical ridge patterns are impossible. It is therefore quite apparent that Judge Beauchamp's proposal to shift the burden of proof is realistic and in line with the most recent scientific conclusions. The premise: �No Duplication of a Ridge Pattern is Possible,� rests on sound biological evidences.
(Editor --� Some interesting and informative observations, relating to the basics, which have stood fast for nearly fifty years since this article first appeared.)
This article was reprinted in �THE PRINT� 10(4), April 1994, pp 3-7
and has been obtained from the online library provided by the
Southern California Association of Fingerprint Officers