JOHANNESBURG, South Africa - Three million years ago, Australopithecus africanus was one of the first human ancestor species to live across the southern African grasslands and forests. A new study of fossil teeth suggests that like modern humans, they breastfed their babies for up to a year after they were born.
The fossil of Lucy is the best known example of an Australopithecus, a species that lived between 2 and 3 million years ago. And like chimpanzees, their children grew quickly and reached adulthood must faster than modern humans.
Previously, research has shown that Australopithecus had a varied diet, made up of fruits, leaves, grass and roots. Due to their habitat, seasonal changes led to periods of abundance and scarcity in food availability. Wet summers provided many food resources, but dry winters had the opposite effect.
Two sets of fossilized teeth found in the Sterkfontein Cave near Johannesburg, South Africa, were studied to understand more about how these early human ancestors responded to seasonal dietary changes.
Teeth have growth rings, much like trees, that determine age as well as minerals gained from the individual's diet. Barium is a mineral in breast milk that can be seen within the rings to determine when a child was breastfeeding and when they were weaned.
Barium accumulation in the two sets of teeth showed steady patterns of accumulating barium after three months of age, which indicated that the behavior lasted for about a year. Then, there were signs of supplementation from other foods. Breastfeeding likely helped the infants survive during a seasonal food shortage.
There was also evidence of cyclical patterns of lithium in the teeth, which suggests food scarcity because it can vary in conjunction with body mass. Food scarcity could last for six moths, which could have led to more breastfeeding or searching for other food sources.
"For the first time, we've gained new insight into the way our ancestors raised their young, and how mothers may have adapted to seasonal food shortages with breastfeeding," said Renaud Joannes-Boyau, lead study author and head of the Geoarchaeology and Archaeometry Research Group at Southern Cross University in Australia.
The teeth were compared with those of modern great apes. The researchers also observed those infants relying more on breast milk during times of food scarcity.
The study, partly funded by the National Institutes of Health, published Monday in the journal Nature.
The researchers believe that the scant resources available during the dry winters may have contributed to the extinction of Australopithecus.
"Seeing how breastfeeding has evolved over time can inform best practices for modern humans by bringing in evolutionary medicine. Our results show this species is a little closer to humans than the other great apes which have such different nursing behaviors," said Christine Austin, study co-author and assistant professor of environmental medicine and public health at the Icahn School of Medicine at Mount Sinai. "These are important findings from an evolutionary perspective, because humans have long childhoods and short breastfeeding periods while apes have longer breastfeeding periods than humans do. We're still in the dark about why or when we made that change and what the effect of more recent major changes in breastfeeding, with agriculture and industrialization, could have on mothers' and babies' health."
Who was Lucy?
When Lucy, the world's most well-known fossil, was discovered sticking out of a shallow Ethiopian stream bed in 1974, she provided new insight about life for early human ancestors 3.18 million years ago. The image of her skeleton -- which is estimated to be 40% complete and considered the best representation of her species, Australopithecus afarensis -- became iconic. Lucy's skeleton is represented by elements of her skull, upper limb, hand, axial skeleton, pelvis, lower limb and foot.
Lucy was small, about 3½ feet tall and 60 pounds. Analysis of her skeleton and teeth shows she had reached maturity, but not unlike chimpanzees, her species matured young. Researchers estimate she was 15 or 16 years old.
She stood up straight, with feet, knees and hips that are similar to ours. If you saw her walking from afar, you would think Lucy was human by her silhouette. But up close, she had a small head, a brain comparable in size to a chimpanzee's, longer arms and hair covering her body.
A 2016 study proposed that she died after falling from a tree, putting her arms out to break her fall in a way that seems distinctly human.