Lab talk: Clues in a Neanderthal's milk tooth
In the latest in our Lab Talk series, we ask Renaud Joannes-Boyau to describe his research and why it matters.
We may have deciphered their DNA but much of Neanderthal life remains a fascinating mystery. New research on an eight-year-old Neanderthal child’s “milk” tooth has revealed the exact age of weaning, giving us a tantalising peek at prehistoric life.
Breastfeeding provides important insights into the social behaviour of our ancestors. The amount of time a primate infant has access to breast milk is important for the species’ life cycle.
Our studies rely on the remarkable durability of teeth; when bone has long since crumbled, teeth remain to tell the tale. As a primate grows, their teeth steadily deposit a layer of enamel each day, just as a tree adds a new ring to its trunk each year. Better still, the enamel layers incorporate elements from the individual’s diet such as barium – which happens to be found at high levels in breast milk.
To reveal an infant’s entire breastfeeding history, we cut a milk tooth in half and use a powerful laser to vaporise a tiny piece of each layer – no deeper than a quarter the width of a human hair. We then measure the amount of barium in each layer with a mass spectrometer.
The oldest parts of a tooth, which form before birth and are still hidden under gums, contain almost no barium – most likely because very little barium passes through the placenta. But with the onset of breastfeeding, barium levels in enamel spike and stay high until solid food is introduced, when barium levels rapidly drop to the prenatal state.
Using the laser technique, we studied the milk tooth of an eight-year-old Neanderthal child who lived 100,000 years ago in what is now Belgium, and found its breastfeeding habits were no different to modern humans and apes. The child was breastfed exclusively for seven months before being introduced to solid food. At 14 months, the infant was abruptly weaned.
Unfortunately, we don’t yet have other Neanderthal milk teeth to compare it to, to see if this was “normal” for the species. But when more teeth are found and investigated, we’ll be able to trace a breastfeeding evolutionary map and see how different – or similar – they were to us.
PAPER: Barium distributions in teeth reveal early-life dietary transitions in primates. Nature, 2013, 498:216–219