Early human species' teeth provide insight into evolution of breastfeeding

(New York, NY - July 15, 2019) -- Mount Sinai researchers working as part of an international team have discovered previously unknown breastfeeding patterns of an extinct early human species by studying their 2-million-year-old teeth, providing insights into the evolution of human breastfeeding practices, according to a study published in Nature in July.

Breastfeeding is a critical aspect of human development, and the duration of exclusive nursing and the timing of introducing solid food to the diet are also important determinants of health in human and other primate populations. Many aspects of nursing, however, remain poorly understood.

Using high-tech methods pioneered at Mount Sinai, the scientists analyzed teeth from Australopithecus africanus (A. africanus), an early human ancestor that lived about 2 to 3 million years ago in South Africa and had both human and apelike features. Scientists reconstructed diet histories using the teeth, measuring preserved chemical biomarkers. The growth patterns of teeth, which resemble tree rings, allow investigators to determine concentrations of barium, an element found in milk, in teeth over time, which yields information about their nursing and dietary patterns.

Researchers found the species breastfed for up to one year and then had six monthly cycles of food scarcity, which could have caused them to fall back to increased breastfeeding or find other food sources.

"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 one of the study's first authors, Christine Austin, PhD, Assistant Professor of Environmental Medicine and Public Health at the Icahn School of Medicine at Mount Sinai and member of Mount Sinai's Institute for Exposomic Research. "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."

Mount Sinai's Institute for Exposomic Research looks into how to develop biomarkers of exposure, and a prime one is measuring chemicals in teeth. Diet is a big part of the exposome--someone's environmental exposure history--and nutritional stress is an exposure that is important to measure to understand overall health after exposures, Dr. Austin said.

"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 the study's lead first author, Renaud Joannes-Boyau, PhD, head of the Geoarchaeology and Archaeometry Research Group (GARG) at Southern Cross University in Australia.

Credit: 
The Mount Sinai Hospital / Mount Sinai School of Medicine