Babies' milk teeth carry their early food history, and this record remains stable for tens of thousands of years.
We know at least six months of exclusive breastfeeding is the best start to a baby’s life. What’s amazing is it seems ancient hominids knew that too.
In a paper published in Nature, we analysed the tooth of an eight-year-old Neanderthal child and showed it was breastfed for its first seven months, and had supplementary non-milk food for a further seven months, before being abruptly weaned completely. The period of exclusive breastfeeding is pretty much in perfect line with today’s maternal guidelines.
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.
In addition to helping fight off infections and provide nutrients required for infant development, breastfeeding also plays an important role in the health of mothers. As a result, the World Health Organisation and UNICEF both recommend mothers continue breastfeeding while introducing infants to non-milk foods.
A remarkable aspect of human evolution is that human infants are weaned much earlier but have much longer childhoods than our closest ape relatives. For example, while a chimpanzee is dependent upon its mother for its first few years of life, it gains independence at around six years of age.
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.
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 within the gum they incorporate elements that circulate 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.
Barium, a naturally occurring element, is found in very small amounts in newborns as the placenta restricts crossing of barium from the mother to the foetus.
It is, however, present in breast milk, and as a baby starts to breastfeed, the “rings” laid down in their milk teeth contain larger amounts of barium.
Similarly, there is a much higher concentration of barium in infant formula compared to breast milk, so the rings formed during formula feeding contain still more barium.
So it is just a matter of identifying the timing of these rings and measuring the amount of barium present in each layer, and presto! There’s your weaning history.
This isn’t confined to humans. We applied this 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.
Spinning the fossil record
We applied the barium measurement technique to an approximately 100,000-year-old 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 seven months before supplementation with non-milk foods, and followed by an abrupt, complete switch to non-milk foods at 14 months. The period of exclusive breastfeeding is similar compared to humans and chimpanzees, but weaning occurred remarkably early in this individual.
Application of the barium measurement technique to more 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. With more samples scientist will be able to get a better consensus of when Neanderthals were weaned.
We hope to apply this new discovery to other fossils from the genus Homo. After all, there are more fascinating discoveries to make about our past.
Christine Austin receives funding from The National Health and Medical Research Council.
Renaud Joannes-Boyau does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.