By examining the fossilised teeth of ancient human ancestors, a team of researchers from the Universities of Bristol (UK) and Lyon (France) has uncovered significant insights into the breastfeeding practices of early humans. The findings, published in Science Advances, show that early Homo species breastfed their infants for much longer periods than their contemporary relatives, such as Paranthropus robustus and Australopithecus africanus.
This discovery provides a rare glimpse into the practice of weaning in our distant ancestors, a behavior that is otherwise difficult to observe in the fossil record. The team analyzed small samples from nearly 40 fossilized teeth belonging to early human relatives found in South Africa. These teeth belonged to species such as Homo, Paranthropus robustus, and Australopithecus africanus—some of the earliest members of the hominin lineage.
To gain insight into the breastfeeding habits of these ancient species, the researchers focused on the stable calcium isotopes found in the tooth enamel. These isotopes are directly influenced by the mother’s milk intake during the early stages of life. By reconstructing the timing of tooth enamel development, the scientists were able to determine when the infants were predominantly breastfed and for how long.
The results of the study revealed that early Homo species—ancestors of modern humans—breastfed for significantly longer periods, up to around three to four years of age. This extended period of breastfeeding is believed to have had a major role in the development of unique human traits, including the brain’s rapid growth during infancy. The researchers suggest that this prolonged period of dependency on breast milk could be linked to the evolution of larger brain sizes and more complex cognitive abilities in the Homo lineage.
In contrast, infants of Paranthropus robustus, which went extinct approximately one million years ago, and Australopithecus africanus—two other hominin species studied—showed different weaning patterns. These species appear to have ceased breastfeeding much earlier, within the first months of life. This shorter duration of breastfeeding in Paranthropus and Australopithecus may have been a reflection of their distinct evolutionary paths, which were shaped by different environmental pressures and social structures.
These differences in nursing behaviors likely correlate with significant shifts in the social structures and reproductive patterns of these ancient hominins. For example, longer breastfeeding periods in early Homo species could have contributed to longer intervals between births, influencing the structure and organization of early human social groups. On the other hand, species that weaned their infants more quickly may have had different social dynamics, perhaps with shorter interbirth intervals and varying parenting strategies.
Dr. Theo Tacail, one of the lead authors of the study and a researcher at the University of Bristol’s School of Earth Sciences, explained that the practice of weaning varies among modern great apes, such as orangutans, gorillas, chimpanzees, and bonobos. This variation in breastfeeding and weaning practices has likely played a significant role in shaping the evolution of human social structures, brain development, and demographic patterns.
He noted that understanding the evolution of weaning practices in early hominins is a challenging task, as the fossil record provides limited direct evidence of these behaviors. While modern animals can offer valuable insights into infant care and nursing practices, interpreting these behaviors in ancient species requires innovative techniques. The use of stable calcium isotope analysis in fossilized teeth, as demonstrated in this study, represents a promising approach to unraveling the complex history of human development.
Tacail emphasized that further research is needed to explore the stable isotope compositions in more fossils, which could offer a deeper understanding of how weaning practices co-evolved with other critical human traits, such as brain size, social behavior, and the structure of early hominin societies. These findings contribute to a more nuanced picture of the lives of our ancient ancestors, shedding light on how the development of nurturing behaviors like breastfeeding may have influenced the course of human evolution.
More information: Théo Tacail et al, Calcium isotopic patterns in enamel reflect different nursing behaviors among South African early hominins, Science Advances (2019). DOI: 10.1126/sciadv.aax3250