Cremated Skeletons Show That Male and Female Differences Are Etched in Bone

Bones keep their secrets, even after burning.

Over the years, archaeologists have developed ways to learn about people’s origins, diets, and even their jobs from their remains. But these techniques are controversial under normal circumstances, and even more dicey when the remains are cremated. Amazingly, however, new research shows it’s possible to glean very detailed information from ancient, damaged, cremated bones — even an individual’s sex.

In a paper published Wednesday in the journal PLOS One, researchers show how to determine the sex of cremated human remains. The team, led by Claudio Cavazzuti, Ph.D., an archaeology research fellow at Durham University in the UK, shows that the new method is just as accurate at determining sex as the typical methods used for analyzing intact skeletons.

Males and females have physical features in their skeletons that indicate their sex — say, the size and dimensions of certain bones — but before this study, scientists didn’t know whether these features could still be measured after cremation. The process, after all, breaks skeletons into shards and dust.

Nevertheless, using the bone fragments from 124 cremated people in Bronze Age and Iron Age Italian burial sites, Cavazzuti’s team looked at 24 of these features among the shards to guess the person’s sex. Then, they looked at the gendered objects that each person was buried with to confirm their guess: “weapons and razors for men; spindle whorls, simple-arch or ‘leech’ fibulas, faïence or glass beads for women.”

As it turns out, the markers can survive cremation.

Out of the 24 features the researchers measured, eight could accurately predict the sex of the individual 80 percent of the the time. This is about as accurate as previously accepted methods for measuring intact skeletons.

“Eight of the 21 analyzed variables showed a degree of accuracy in the sex assessment that was equal to or greater than 80%, a value generally considered a benchmark for evaluating the utility of a determination method,” they write.

These eight features were measured in bones known as the radius, patella, mandible, talus, femur, first metatarsal, lunate, and humerus. The most tell-tale feature of the bunch is the head of the forearm bone known as the radius, which differs significantly between males and females. So while the average person may not be able to look at a skeleton and tell the sex of the person it belonged to, the researchers figured out how to reconstruct it from these small features of bone fragments.

This new study is a big deal for archaeologists because cremation is well known to deform bones, not just by shattering them into fragments, but also by stretching and twisting them as they heat up. If this study’s findings are confirmed, it will confirm that human bones retain a clearly measurable level of sexual dimorphism — the physical difference between males and females — even after being deformed by fire. The researchers hope that others can learn from it and apply the findings to decoding the demographics of ancient populations that were previously a mystery.

“This is a new method for supporting the sex determination of human cremated remains in antiquity,” Cavazzuti said. “Easy, replicable, reliable.”

Abstract: Sex estimation of human remains is one of the most important research steps for physical anthropologists and archaeologists dealing with funerary contexts and trying to reconstruct the demographic structure of ancient societies. However, it is well known that in the case of cremations sex assessment might be complicated by the destructive/transformative effect of the fire on bones. Osteometric standards built on unburned human remains and contemporary cremated series are often inadequate for the analysis of ancient cremations, and frequently result in a significant number of misclassifications. This work is an attempt to overcome the scarcity of methods that could be applied to pre-proto-historic Italy and serve as methodological comparison for other European contexts. A set of 24 anatomical traits were measured on 124 Bronze Age and Iron Age cremated individuals with clearly engendered grave goods. Assuming gender largely correlated to sex, male and female distributions of each individual trait measured were compared to evaluate sexual dimorphism through inferential statistics and Chaktaborty and Majumder’s index. The discriminatory power of each variable was evaluated by cross-validation tests. Eight variables yielded an accuracy equal to or greater than 80%. Four of these variables also show a similar degree of precision for both sexes. The most diagnostic measurements are from radius, patella, mandible, talus, femur, first metatarsal, lunate and humerus. Overall, the degree of sexual dimorphism and the reliability of estimates obtained from our series are similar to those of a modern cremated sample recorded by Gonçalves and collaborators. Nevertheless, mean values of the male and female distributions in our case study are lower, and the application of the cut-off point calculated from the modern sample to our ancient individuals produces a considerable number of misclassifications. This result confirms the need to build population- specific methods for sexing the cremated remains of ancient individuals.