Maternal secrets of our earliest ancestors unlocked

A stunning new research result published today in Nature reveals for the first time the breastfeeding and weaning habits of an early human ancestor that lived between 3 and 2 million years ago in South Africa.

As part of an international research team – led by Southern Cross University and Monash University – Professor Andy Herries, Head of La Trobe University’s Archaeology and History Department, helped analyse more than two-million-year-old teeth from Australopithecus africanus fossils found in South Africa.

The research team revealed that infants were breastfed continuously from birth to about one year of age. In addition, the study has shown nursing appears to have continued in a cyclical pattern in the early years for infants, as seasonal changes and food shortages caused the mother to supplement gathered foods with breastmilk.

“For the first time, we gained new insight into the way our ancestors raised their young, and how mothers had to supplement solid food intake with breastmilk when resources were scarce,” said geochemist Dr Joannes-Boyau from the Geoarchaeology and Archaeometry Research Group (GARG) at Southern Cross University.

Australopithecus africanus was the first human species to inhabit what was likely a relatively harsh limestone landscape in South Africa. This research potentially shows that living in these environments was difficult for our early ancestors, particularly as climate began to change around 2.3 to 2 million years ago and this may have led to their ultimate extinction not long after this time,” said Professor Andy Herries, Head of La Trobe University’s Archaeology and History Department.

“These finds suggest for the first time the existence of a long-lasting mother-infant bond in Australopithecus. This makes us to rethink on the social organisations among our earliest ancestors,” said Dr Fiorenza, who is an expert in the evolution of human diet at the Monash Biomedicine Discovery Institute (BDI).

“Fundamentally, our discovery of a reliance by Australopithecus africanus mothers to provide nutritional supplementation for their offspring and use of fallback resources highlights the survival challenges that populations of early human ancestors faced in the past environments of South Africa,” said Dr Adams, an expert in hominin palaeoecology and South Africa sites at the Monash BDI.

For decades there has been speculation about how early ancestors raised their offspring. With this study, the research team has opened a new window into our enigmatic evolutionary history. Australopithecus africanus lived from about two to three million years ago during a period of major climatic and ecological change in South Africa, and the species was characterised by a combination of human-like and retained ape-like traits. While the first fossils of Australopithecus were found almost a century ago, scientists have only now been able to unlock the secrets of how they raised their young. Teeth grow similarly to trees; they form by adding layer after layer of enamel and dentine tissues every day. Thus, teeth are particularly valuable for reconstructing the biological events occurring during the early period of life of an individual, simply because they preserve precise temporal changes and chemical records of key elements incorporated in the food we eat. Specialised laser sampling techniques were used to vaporise microscopic portions on the surface of the tooth. The gas containing the sample is then analysed for chemical signatures with a mass spectrometer – enabling researchers to develop microscopic geochemical maps which can tell the story of the diet and health of an individual over time.

“We can tell from the repetitive bands that appear as the tooth developed that the fall back food was high in lithium, which is believed to be a mechanism to reduce protein deficiency in infants more prone to adverse effect during growth periods,” Dr Joannes-Boyau said.

“This likely reduced the potential number of offspring, because of the length of time infants relied on a supply of breastmilk. The strong bond between mothers and offspring for a number of years has implications for group dynamics, the social structure of the species, relationships between mother and infant and the priority that had to be placed on maintaining access to reliable food supplies,” he said.

“This finding underscores the diversity, variability and flexibility in habitats and adaptive strategies these australopiths used to obtain food, avoid predators, and raise their offspring,” Dr Adams emphasised.

“This is the first direct proof of maternal roles of one of our earliest ancestors and contributes to our understanding of the history of family dynamics and childhood,” concluded Dr Fiorenza.

Dr Joannes-Boyau conducted the analyses at the Geoarchaeology and Archaeometry Research Group at Southern Cross University in Lismore NSW and at the Icahn School of Medicine at Mount Sinai in New York. This work was conducted as part of an ARC Discovery Project led by Professor Herries at La Trobe University, looking at what drove changes in human species, and their diversity between 2.6 and 1.8 million years ago in South Africa.

The team will now work on species that have evolved after 2 million years, including the cave site of Drimolen where Professor Herries runs an international field school in Palaeoanthropology each June, to develop the first comprehensive record of how infants were raised throughout a critical time in our evolutionary history at the extinction of Australopithecus and the first occurrence of our genus, Homo.

Read the full paper in Nature titled Elemental signatures in Australopithecus africanus teeth reveal seasonal dietary stress.

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