Dermatoglyphics refers to the study of the patterns of skin (dermal) ridges present on the fingers, palms, toes, and soles of human and nonhuman primates.  Most commonly, fingerprints are used in anthropological studies of dermatoglyphics, though other prints are taken in some situations (like footprints taken of newborns at the hospital).  Currently some researchers are advocating that anthropological dermatoglyphic studies be expanded to include palm and footprints.

    These ridges also appear on the prehensile surfaces of some NHP tails.  Ridges themselves are thought to serve an adaptive function – namely, to improve gripping through friction.  Nerve endings along the ridges enhance touch, enhancing tactile stimulation.  However, the great variety of patterns suggests that no particular pattern has been selectively favored (it appears the patterns are selectively neutral).

    This selective neutrality among the fingertip ridge patterns makes them ideal for microevolutionary studies, as research has indicated that about 90% of the variation in patterns is inherited, albeit in a complicated, polygenic manner.  It is also thought that the alleles involved probably occur on different chromosomes; this has been suggested by the fact that several congenital chromosomal disorders produce specific alterations of fingerprint patterns.   Factors contributing to fingerprints' utility:

1.  Uniqueness.  Each person’s pattern is unique – no two fingers are unique, and no two people share the same pattern (environmental influences make even monozygotic twins’ prints differ).

2.  Stability.  Fingerprints are essentially unchanging and permanent, becoming fixed during the fourth fetal month and only increasing in size thereafter.

3.  Genetic.  Fingerprints are determined mostly genetically and are selectively neutral, making them very useful for evolutionary studies at all levels, from single families to the entire globe.  Additionally, some authorities believe that because dermatoglyphic patterns are influenced by many separate genes on multiple chromosomes, they may be even more reliable for these microevolutionary studies than monogenic discrete traits (and some monogenic abnormalities) that are also studied for this purpose, because a polygenic trait is less likely than a monogenic trait to be disrupted by chance factors.  (Currently work is also underway to determine whether dermatoglyphic variation tracks well with certain commonly studied DNA variation.  If this turns out to be the case, dermatoglyphics could be used as a substitute for DNA studies in situations where expense is a concern, or where minimally invasive sampling procedures are necessary.)

    Dermatoglyphics is used in a variety of different contexts.  Fingerprints may be used in forensics to help identify murder victims as well as to identify possible suspects based on the fingerprints they may leave at the crime scene.  Indeed, fingerprints are useful in any situation requiring precise identification.  Because fingerprint patterns are hereditary, family members will share certain similarities, with closer relatives having more similar patterns than more distant relations.  Their correlation with genetic abnormalities already mentioned allows fingerprints to aid in diagnosis.  Familial inheritance patterns can be studied, and different populations can be compared.  This last is especially helpful in conjunction with other techniques such as anthropometry and genetic anthropology; biological similarities among populations can be assessed, and their evolutionary relationships explored.  So, some major uses of fingerprint and other dermatoglyphic data:

1.  Identification.  Forensic fingerprint examiners first classify latent fingerprints into one of the three broad pattern categories mentioned below, then make a specific identification on the basis of a number of more detailed features than those we will examine in this lab.

2.  Link with nonhuman primates.  Investigation into primate dermatoglyphic patterns has not been exploited to nearly the extent that it might be; it is possible that further study might reveal dermatoglyphic links among closely related species, and perhaps even link humans to our closest primate relatives.

3.  Small-scale microevolutionary studies.  Dermatoglyphics have been used to investigate mating and migration patterns among closely related villages and towns, for instance; in such cases fingerprints can both support ethnographic data and possibly reveal relatively recent changes in mating patterns.

4.  Larger scale microevolutionary studies.  These involve identifying larger scale patterns of geographic dermatoglyphic variation, with the intent of illuminating past migration patterns and population movements.

    There are three categories of patterns: arch, loop, and whorl.   Fingerprints are first classified into one of these categories, and then further analyses are performed, on the basis of certain landmarks defined in your manual.  (Note that there are many variants formally identified within these three categories.)  You will be looking for a few things:

Triradius:  A point in the ridge system from which three ridges diverge.  Also called a delta.
Core:  The centermost ridge of a pattern.
Ridge count:  The total number of ridges between – but not including – a triradius and a core.

1. Arches.  These are patternless areas with NO triradius or core.  A plain arch follows this pattern, but a tented arch has one of each but a zero ridge count – in that case the triradius and the core are immediately next to each other, and since you count neither of them in a ridge count, the ridge count is zero.

2. Loops.  These have one triradius and one core, and one ridge count (variable from person to person).  You will sometimes see a distinction made between ulnar and radial loops, depending upon the direction towards which they open.

3. Whorls.  These have two triradii and a single core; thus, the ridge count will need to be taken in two directions (along ridge count lines drawn from triradius to core).