Your teeth can reveal a lot about you - including where you grew up. They're also the part of you that's most likely to endure long after you've died. Now some ancient teeth are revealing dating habits that date back a million years.
Oxford researchers examined various fossils from our ancestor species Australopithecus. The remains date back to between 1.8 and 2.2 million years ago, and they were found in two caves in South Africa. Analysis of these fossil teeth reveal that the Australopithecus women were much more likely to have minerals in their teeth from faraway regions than those from males.
This means that, millions of years ago, it was women who went elsewhere to find a mate, which isn't necessarily intuitive if you think in terms of modern social customs. Of course, it can be dicey to compare how we do things today (or in the last few hundred or even few thousand years) with what family structures were like in our hominid ancestors. Indeed, this insight into how Australopithecus families formed is backed up by chimp social behavior, as female chimps also leave their original groups in search of mates.
So how can we tell all this from teeth? The key is strontium, an element found in soil that moves from plants to smaller animals to humans. The ratio of two particular strontium isotopes can let researchers locate its source with remarkable accuracy. Teeth soak up these strontium isotopes while they're forming - in other words, while they still have their pre-adult teeth - which means they preserve a record of where that person or animal was a child.
As for how we tell the difference between male and female teeth - well, it's just a matter of size. Male hominids are generally larger than female hominids, and the bigger teeth were much, much more likely to show strontium signatures that placed their childhoods in the caves where they died.
While the sample size is small, the researchers are convinced that they're onto something here. The only problem will be figuring out how best to follow up this initial research. Strontium testing can be quite destructive to the fossils, which means researchers are wary of doing them unless absolutely necessary. But the team hopes to find some more Australopithecus teeth to test, and then also to see whether other hominids - including our more recent ancestor Homo erectus - had similar customs when it came to finding a mate.