Scientists led by Dr Manish Arora from the Icahn School of Medicine at Mount Sinai have reported that they can now use fossil teeth to calculate when a Neanderthal baby was weaned.

Their new technique is based in part on knowledge gained from studies of teeth from human infants and from macaques at the California National Primate Research Center.

Prof Katie Hinde from Harvard University, co-author of a paper published in the journal Nature, explained: “just as tree rings record the environment in which a tree grew, traces of barium in the layers of a primate tooth can tell the story of when an infant was exclusively milk-fed, when supplemental food started, and at what age it was weaned.”

The scientists were able to determine exact timing of birth, when the infant was fed exclusively on mother’s milk, and the weaning process, from mineral traces in teeth. By studying monkey teeth and comparing them to their records, they could show that the technique was accurate almost to the day.

After validating the technique with monkeys, the scientists applied it to human teeth and a tooth of Neanderthal (Homo neanderthalensis).

They found that the Neanderthal baby was fed exclusively on mother’s milk for seven months, followed by seven months of supplementation – a similar pattern to present-day humans. The technique opens up extensive opportunities to further investigate lactation in fossils and museum collections of primate teeth.

“Although there is some variation among human cultures, the accelerated transition to foods other than mother’s milk is thought to have emerged in our ancestral history due, in part, to more cooperative infant care and access to a more nutritious diet. Shorter lactation periods could mean shorter gaps between pregnancies and a higher rate of reproduction. However, there has been much debate about when our ancestors evolved accelerated weaning,” Prof Hinde said.

For the past few decades researchers have relied on tooth eruption age as a direct proxy for weaning age. Yet recent investigations of wild chimpanzees have shown that the first molar eruption occurs toward the end of weaning.

“By applying these new techniques to primate teeth in museum collections, we can more precisely assess maternal investment across individuals within species, as well as life history evolution among species,” Prof Hinde concluded.

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Bibliographic information: Christine Austin et al. Barium distributions in teeth reveal early-life dietary transitions in primates. Nature, published online May 22, 2013; doi: 10.1038/nature12169