Skeletons pose riddles. While they can provide gender and ancestry and what someone looked like in life, they do not immediately provide some other key information, like age at the time of death.
For example, a young athlete could have worn-out joints, while an older person may have less wear and tear. Both could complicate the aging of bones—and therefore the process of making an identification.
But a joint in the pelvic area known as the pubic symphysis has been used as a reliable bone clock of sorts, since it is mostly immoveable. Because of this, it ages relatively consistently compared to other structural parts of the body. Anthropologists can look at the whole joint and generally estimate age at death based on its shape and texture.
For years that estimation has been based on formulas relying on subjective observations, the best known being the Suchey-Brooks method, which relies on the contours of the joint’s surface. But now a Stanford University anthropologist and her team have come up with a more precise analysis based on advanced 3-D imaging of the shape and a growing database of samples, as unveiled last week in the Journal of Forensic Sciences.
“My goal was to say, ‘Let’s look at this computationally,’ so we can try to figure out a way to capture the same things we’re seeing visually, but do it from a mathematical way using continuous data,” said Bridget Algee-Hewitt, the leader of the team, in a recent interview with Forensic Magazine. “With biometrics now, they’re taking all those thousands of points of a fingerprint to match them ... and it’s no longer that visual world of ridges and arches. We can do the same thing with the pubic symphysis.”
Algee-Hewitt, already known for her various work with ancestry information within CODIS markers and determining ancestry information from a combination of skull measurements and DNA, also presented the intensive method at a workshop at last month’s American Academy of Forensic Sciences conference in New Orleans.
“It went really well,” she said, adding that some of the 30 participants were from the Gendarmerie Nationale in Algeria, Korean military officials and also from the Joint POW/MIA Accounting Command. “They were all from an applied forensic focus … Some really good people doing extremely serious forensic endeavors.”
The method relies on three algorithms to provide quantitative estimations that can be reproduced, and take the subjective error out of the process. One calculation describes the gradual flattening of the surface of the bone. A second looks at the energy that would transform a young person’s ridged and furrowed bone to a flatter shape. A third part of the equation calculates the gradual formation of a rim around the ventral edge of the bone, and how it would later erode with time.
The hyper-detailed measurements include 40,000 points per square inch. The team, consisting of Dennis Slice, Jieun Kim and Detelina Stoyanova at Florida State University, and doctoral student Cristina Figueroa-Soto at the University of Tennessee in Knoxville, worked alongside Algee-Hewitt to compile the big-data results.
Taken together, the results have started to provide more accurate age estimations. Using an initial group of 93 known bodies, the method was able to place as many 34 percent of the bones within five years of the true age of death. More than 50 percent of the estimates were within 10 years of the correct age, and about 75 percent were within 15 years, Algee-Hewitt and the other scientists report.
The new computerized models did less well for the 20-40 age group—but they were more accurate for all other age groups, the team explains.
The method could be an important tool added to the forensic toolbox, according to some experts.
Erin Kimmerle, an anthropologist at the University of South Florida well-known for her scientific investigations at the Arthur G. Dozier School for Boys and also as the chief anthropologist for the United Nations in the former Yugoslavia in the wake of the ethnic cleansing wars of the 1990s, did her dissertation on the pubic symphysis. Kimmerle said scientists are generally hesitant to narrow down the age range too far to erroneously exclude possible ages, considering the margin of error in the applied science. But the latest statistical work from Algee-Hewitt and her team are an important advance, she added.
“I think it’s really exciting, what they’re doing,” Kimmerle said. “It’s necessary, and can definitely add more to our understanding of aging.”
The work is funded by an ongoing, multiyear National Institute of Justice grant. Algee-Hewitt, who has also made progress into skull analysis by fusing her two backgrounds—traditional anthropology with the data-heavy DNA analysis of large populations—said the 3-D scanning work of the pubic symphysis could potentially translate to analysis of other parts of the skeleton, like the ends of the ribs, to increase the statistical accuracy with large enough sample sizes.