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An international research team led by Dr Renaud Joannes-Boyau of Southern Cross University, and by Dr Luca Fiorenza and Dr Justin W. Adams from Monash University, published the details of their research in Nature magazine.

Australopithecus africanus mothers breastfed their infants for the first 12 months after birth, and continued to supplement their diets with breastmilk during periods of food shortage. Tooth chemistry analyses enabled scientists to 'read' the growth rings of the more than two-million-year-old teeth to demonstrate why early human ancestors had fewer offspring and extended parenting role Extended parental care is considered one of the hallmarks of human evolution. "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," explains geochemist Dr Joannes-Boyau from the Geoarchaeology and Archaeometry Research Group (GARG) at Southern Cross University.

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"These finds suggest for the first time the existence of a long-lasting mother infant bond in Australopithecus. This makes us rethink 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 populations of early human ancestors faced in South Africa," says Dr Adams, an expert in hominin palaeoecology and South African sites at the Monash BDI.

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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.

Using specialised laser sampling techniques to vaporise microscopic portions on the surface of a tooth, scientists capture the gas given off by the vaporised tooth enamel — then analyse for chemical signatures using a mass spectrometer. All this allows researchers to develop microscopic geochemical maps which can tell the story of the diet and health of an individual over time. Dr Joannes-Boyau conducted the analyses were conducted 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.

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Teeth grow similarly to trees; by adding layer after layer of enamel and dentine tissues each day. So they are particularly valuable for reconstructing biological events during the early period of life as they preserve precise changes and chemical records of key elements incorporated in the food we eat.

By developing micro geochemical maps, scientists were able to 'read' successive bands of daily signal in teeth, which provide insights into food consumption and stages of life. Previously the team had revealed the nursing behaviour of our closest evolutionary relatives, the Neanderthals. With this latest study, the international team has analysed teeth that are more than ten times older than teeth of Neanderthals.

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"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.

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The team will now work on species that have evolved since, to develop the first comprehensive record of how infants were raised throughout our long history.

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Abstract
Reconstructing the detailed dietary behaviour of extinct hominins is challenging1—particularly for a species such as Australopithecus africanus, which has a highly variable dental morphology that suggests a broad diet2,3. The dietary responses of extinct hominins to seasonal fluctuations in food availability are poorly understood, and nursing behaviours even less so; most of the direct information currently available has been obtained from high-resolution trace-element geochemical analysis of Homo sapiens (both modern and fossil), Homo neanderthalensis4 and living apes5. Here we apply high-resolution trace-element analysis to two A. africanus specimens from Sterkfontein Member 4 (South Africa), dated to 2.6–2.1 million years ago. Elemental signals indicate that A. africanus infants predominantly consumed breast milk for the first year after birth. A cyclical elemental pattern observed following the nursing sequence—comparable to the seasonal dietary signal that is seen in contemporary wild primates and other mammals—indicates irregular food availability. These results are supported by isotopic evidence for a geographical range that was dominated by nutritionally depauperate areas. Cyclical accumulation of lithium in A. africanus teeth also corroborates the idea that their range was characterized by fluctuating resources, and that they possessed physiological adaptations to this instability. This study provides insights into the dietary cycles and ecological behaviours of A. africanus in response to food availability, including the potential cyclical resurgence of milk intake during times of nutritional challenge (as observed in modern wild orangutans5). The geochemical findings for these teeth reinforce the unique place of A. africanus in the fossil record, and indicate dietary stress in specimens that date to shortly before the extinction of Australopithecus in South Africa about two million years ago.

Authors
Renaud Joannes-Boyau, Justin W. Adams, Christine Austin, Manish Arora, Ian Moffat, Andy I. R. Herries, Matthew P. Tonge, Stefano Benazzi, Alistair R. Evans, Ottmar Kullmer, Stephen Wroe, Anthony Dosseto & Luca Fiorenza.

Acknowledgements
Part of this study was funded by Monash University seed grant to L.F., J.W.A., A.R.E., A.I.R.H., S.W., S.B., O.K. and R.J.-B. A.I.R.H., J.W.A. and R.J.-B. received funding from the Australian Research Council Discovery Grant DP170100056. C.A. is supported by NICHD award R00HD087523. I.M. is supported by an Australian Research Council DECRA Fellowship (DE160100703), a Commonwealth Rutherford Fellowship from the Commonwealth Scholarship Commission and a Research Associate position from Homerton College. M.A. is supported by the US National Institutes of Environmental Health Sciences Grants U2CES026561 and DP2ES025453. We thank the South African Heritage Resources Agency (SAHRA), B. Zipfel from the Evolutionary Studies Institute of the University of Witwatersrand and M. Tawane from the Ditsong National Museum of Natural History for granting the export permit for the samples for analyses; C. Lawrence and K. Simon-Menasse from Perth Zoo, who provided access to modern orangutan dental material; and K. Schultz for comments on this manuscript.

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