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Ideas | Kelly Kasulis

Something to chew on: prehistoric sex roles

A new technique can determine biological sex from a single tooth.
A new technique can determine biological sex from a single tooth.(Jelmer Eerkens)

As any archeologist or anthropologist can tell you, most of our ancestors’ bodies were not perfectly preserved. They were often burned, buried, or left to decay under the sweltering sun. For researchers, that’s meant difficulty determining even the most basic biology of some specimens. Now, a study from the University of California, Davis, has identified a new way to determine the sex of bodies and even sort out ancient social inequalities between males and females: examining teeth.

Until recently, researchers either needed complicated and expensive DNA analysis or access to specific bones, like the pelvis, to determine sex. Even then, there were complications: DNA is fragile and difficult to preserve.

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That’s why UC Davis researchers decided to examine toothy proteins. Using acid, they dissolved enamel from specimens dating as far back as 7,000 years. Then they heated it, ground it up, added an enzyme, and examined it using a mass spectrometer. By looking at the amino acid sequence in these proteins, they were able to guess whether the tooth belonged to a male or female.

“Up to this point, it has been a bit of a black hole when you’re talking about anatomy,” said Glendon Parker, one of the study’s authors and an adjunct associate professor at the UC Davis Department of Environmental Toxicology. “We took advantage of a really cool coincidence: The toughest tissue in the body just happens to have a protein from the most characterized, sex-specific gene.”

But why is knowing the sex of ancient remains so important? “In both ancient and modern societies around the world, sex is often a strong determinant of your identity within a society,” said Jelmer Eerkens, a professor of anthropology at the UC Davis and an author of the study. “It determines things like whether you can inherit land, when you get married, and whether you need to move to your new spouse’s village [or vice-versa].”

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In general, teeth can reveal a lot about a person’s life. Wear patterns give clues to a person’s diet, while tartar can preserve bacteria or food residue, even in human relatives who lived some 50,000 years ago. But examining proteins left behind in teeth could also potentially reveal how different sexes lived back in the day — and whether they were treated equally.

“If you look at nursing patterns for example, we know from wild primates that mothers invest differently in different sexes of offspring,” said Tanya Smith, a professor at the Australian Research Center for Human Evolution at Griffith University. “Now we can potentially look into whether ancient [human] mothers were nursing their daughters as much as their sons. That’s really exciting.”


Kelly Kasulis is a freelance journalist. Follow her on Twitter: @KasulisK.