Analyzing ancient fingerprints’ ridge breadth and density, anthropologist Kent Fowler and colleagues have discovered the age and sex of those who left marks on ancient pottery, revealing never-before-understood clues as to how labor was divided between people 4,700 years ago.
Fowler’s work was partially informed by current fingerprint analyses methods in forensic literature. Conventional fingerprint analysis focuses on identifying individuals based on the occurrence of specific combinations of ridge characteristics, such as the bifurcations, lakes, spurs, and crossovers that make up the whorls, loops, tents, and arches of print patterns. Other research has concentrated on determining age from the analysis of ridge breadth and sex from the analysis of ridge density using latent prints from crime scenes. As Fowler dug more and more into the published research, he noticed something interesting—researchers examined either ridge breadth or ridge density in a study, but not both; and archaeologists have continually attempted to determine age and sex using ridge breadth data even though no forensic research has shown that ridge breadth is sexually diamorphic.
“I could not figure out why measures of ridge breadth and density were not being taken for each individual print and the two results combined to propose a more robust identification of age and sex,” Fowler told Forensic.
So, Fowler took matters into his own hands and joined the two, proposing a new method. His age/sex identification matrix is an interpretive framework that incorporates the generalized cut-offs for age based upon ridge breadth data and the cut-offs for sex based upon ridge density data. In the matrix, a median age of 10 distinguishes children from early adolescents, while biological adulthood is set at 20, a time when growth is minimal and most of the skeleton has ossified. According to the paper published in the Journal of Archaeological Method and Theory, the position of ridge breadth and density values within the matrix improves the estimate of age and sex determination for prints of unknown origin.
“Importantly, the matrix resolves a significant interpretive problem in age estimations from ridge breadth. It more clearly distinguishes adolescent and adult male and female prints, thus refining the ambiguous adult/adolescent group, and allows prints to be classified into one of six age/sex categories,” the paper reads.
Using a sample of more than 400 pottery sherds, Fowler and his team examined 38 of the clearest partial and whole prints. Based on mean ridge breadth, most fingerprints were made by adult males (67 percent), in addition to adolescent males (30 percent). Ridge density data confirmed the sex of the fingerprints, proving especially vital in identifying six prints on the cusp of the gender-specific ridge density value.
“The six values [on the cusp] are only marginally above the threshold for identifying females. Nevertheless, because none of the six prints fall strictly below [the threshold] there is a strong statistical likelihood for a respective 67:33 ratio of male to female prints. This is why it is important to consider both ridge breadth and ridge density data when interpreting prints, as there is a low probability that these six prints could belong to males if they have correspondingly high ridge breadth values,” the authors write in their paper.
Thus, in this specific study—as well as future ones—the identification matrix provides a more robust interpretation of fingerprint data by comparing both ridge breadth and ridge density data from archaeological prints against empirical data from forensic studies.
“Many influences go into developing a method such as this,” Fowler said. “For us, we needed to compare knowns with unknowns, we needed to understand human biological development and how this is manifested in hands, the development of motor skills at different ages, how work impacts hand size and robustness, the thermal properties of clays, how objects were made and how and when they could be handled, etc. So, forensic research was a vital component in developing a broader, multi-dimensional method.”
That’s not to say, however, that the roles are never reversed. In fact, archaeological methods have greatly impacted forensic research, informing how data is collected at crime scenes as well as the recovery of buried remains.
“My hope is that when archaeologists interested in print research do obtain and publish new data they have collected from present-day populations to aid their research, that this will be brought to the attention of forensic scientists and they will find it useful in their own work,” Fowler said. “At least now, in such a connected world, we can raise the consciousness of forensic scientists, developmental psychologists, biological anthropologists, and archaeologists that there is another way we can work together, and in the process, enrich our own disciplines.”
Photo: Fingerprints left on this pottery show the index and middle fingers of the right hand on the bottom of the storage vessel. Scale is 5 cm. Credit: Kent Fowler.