Trace element and isotope analyses in fossil teeth: reconstructing the past with biomarkers

Barium distributions in teeth reveal early-life dietary transitions in primates. Nature 2013
(DOI: 10.1038/nature12169)

The transition from maternal milk to non-milk foods is a fundamental aspect of primate evolution and an important determinant of health in contemporary human populations. A remarkable aspect of human evolution is that human infants are weaned much earlier but have much longer childhoods than our closest ape relatives. There is much debate about when early weaning occurred in the hominin lineage. Reliable markers of early diet transitions in ancient hominins and non-human primates have been largely unavailable until now. In the paper recently published by Nature (DOI: 10.1038/nature12169), we show that these early life dietary transitions are recorded in teeth and remain stable in fossil remains from thousands of years ago. Teeth grow following a regular pattern that creates permanent daily lines, like the rings found in trees. Teeth also carry a ‘birth certificate’ in the form of an accentuated line visible in baby teeth and first permanent molars. As the teeth grow they incorporate elements that are circulating the body after uptake from food, water and environmental sources. Using special analytical chemistry and microscopy techniques we are able to trace changes in the element content of teeth with precision timing.

Birth and diet transitions from breast milk to infant formula were first observed in teeth from children with known diet histories. Barium, a naturally occurring element, increased at birth with the introduction of breast milk and increased further when infant formula was introduced. These increases in barium are due to the restriction of barium across the placenta and a much higher barium concentration in infant formula compared to breast milk. We also applied the technique to teeth from macaques with known dietary histories. Again, barium increased at birth but decreased with supplementation of other foods and returned to levels seen before birth at the completion of weaning.

We then applied this technique to a Middle Paleolithic Neanderthal tooth from Belgium and found a similar barium pattern as that seen in the macaques. The pattern indicated that this Neanderthal was breastfed for about 7 months before supplementation with non-milk foods, followed by an abrupt cessation of weaning at 1.2 years of age. The period of exclusive breastfeeding is similar compared to humans and chimpanzees but weaning has occurred remarkably early in this individual.

Application of this technique to additional samples will enable the evaluation of theories regarding weaning patterns and life histories of hominin species and comparisons across primate species which have important implications for models of population growth and species replacement. Additionally, breastfeeding is believed to reduce the risk of many illnesses in children and this technique will aid in studies of contemporary human health.

 

Credits: Ian Harrowell, Christine Austin, and Manish Arora

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