- New research brings to light for the first time the evolution of maternal roles and parenting responsibilities in one of our oldest evolutionary ancestors
- 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 enable scientists to ‘read’ more than two-million-year-old teeth
- Finding demonstrates why early human ancestors had fewer offspring and extended parenting role
For some of our earliest ancestors, production of a mother's breast milk was not just limited to nursing very young infants, astonishing new research has revealed.
Analysis of more than two-million-year-old teeth from Australopithecus africanus fossils found in South Africa show that breast feeding was strategically used after infants were weaned so that mothers could nourish children through seasonal food shortages.
“For years after an initial 12 month ‘weaning’ period, at least some of our long-extinct female human ancestors could switch their milk supply off and on for years to sustain their offspring when times got tough," said Professor Stephen Wroe, Director of the University of New England's Function, Evolution & Anatomy Research (FEAR) Lab and a collaborator in the study.
This doesn’t simply reveal an interesting aspect of ancient human biology. It also tells us that by two million years ago these ancestral mothers had developed very strong and persistent relationships with their children.
The research, published in the journal Nature today, was produced by an international team led by Dr Renaud Joannes-Boyau of Southern Cross University, and by Dr Luca Fiorenza and Dr Justin W. Adams from Monash University.
Extended parental care is considered one of the hallmarks of human evolution. The ground-breaking study of fossilised Australopithecus africanus teeth has shown that infants of the extinct hominid were breastfed continuously from birth to about one year of age.
Laser sampling of the fossil teeth revealed that nursing appeared to continue in a cyclical pattern in the early years for infants, presumably 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.
“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).
Dr Adams, an expert in hominin palaeoecology and South Africa sites at the Monash BDI, added that along with the fresh insight into how Australopithecus mothers provided nutritional supplementation for their offspring, the study also highlights the survival challenges that populations of early human ancestors faced in the past environments of South Africa.
Image: Skull of Australopithecus africanus specimen STS 71 - (Credit Fiorenza)
Australopithecus africanus lived from about two to three million years ago during a period of major climatic and ecological change in South Africa. The species was characterised by a combination of human-like and retained ape-like traits.
The first fossils of Australopithecus were found almost a century ago, but scientists have only now been able to unlock the secrets of how they raised their young by using specialised laser sampling techniques 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. 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.
Teeth grow similarly to trees; layer after layer of enamel and dentine tissues is added daily. This accumulation of layers is valuable for reconstructing the biological events of a growing individual, because they preserve precise temporal changes and chemical records of key elements incorporated in the food eaten.
Micro-geochemical maps now allow scientists to ‘read’ successive bands of daily signal in teeth, which provide insights into food consumption and stages of life.
Previously this team had used the same techniques to reveal 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.
“We can tell from the repetitive bands that appear as the Australopithecus tooth developed that the fallback 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."
“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.”
The team will now work on species that have evolved since Australopithecus, to develop the first comprehensive record of how infants were raised throughout history.
Full Nature paper: Elemental signatures in Australopithecus africanus teeth reveal seasonal dietary stress (https://www.nature.com/articles/s41586-019-1370-5)
