A team of scientists has announced that they can now determine the sex of a human skeleton from a single tooth, by looking at traces of protein.

Published in the Journal of Archaeological Science, the study led by the University of California, Davis used mass spectrometry – looking at the various chemicals in a sample – to analyze proteins in teeth.

In particular, they looked at the genes of amelogenin proteins. Females have amelogenin-X genes, while males have both amelogenin-X and Y.

The researchers studied 40 enamel samples from 25 individuals, which included both adults and children, dating back 100 to 7,300 years from sites in North America and Peru, alongside some modern teeth. In all the samples they found amelogenin-X, while only about half had amelogenin-Y, suggesting they were male.

One issue was that a tooth that had no amelogenin-Y could be a false negative if there was simply too little of the Y gene to detect. So the team used a statistical method to work out if it could be a false negative based on how much amelogenin-X was present.

Normally the biological sex of human remains is determined by looking at features in bones that are different in males and females, such as the pelvis. But these changes aren’t apparent in children, while an incomplete skeleton can make working out the sex difficult.

California
A tooth from a European-American buried in San Francisco in the 1850s. Jelmer Eerkens/UC Davis

The other option is DNA evidence, but this is expensive and difficult, and requires sterile conditions. But teeth, which are often found at archaeological sites, could offer a novel way to work out the sex of a skeleton – alongside other interesting pieces of information.

“Wear patterns on the tooth can tell us about diet,” said Jelmer Eerkens from the UCDavis, a co-author on the study. He added that plaque can reveal the bacteria in a person’s mouth, radiocarbon dating can reveal the age of the person, and isotope data can show their movement.

The team said measuring the amount of amelogenin in teeth could be used alongside existing methods to more accurately determine a skeleton’s biological sex. And it also highlights just how important teeth are to archaeologists in working out the history of human remains.

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