We know more and more about the origins of humanity. And one thing is becoming increasingly clear: it is the way we care for our young that has made us human.
In 2021, a fascinating documentary was shown on the French television channel France 5: Kromdraaï, à la découverte du premier humain.[1]
On this site of Kromdraaï (South Africa), the paleoanthropologist José Braga recently discovered the bones of two children who lived at the same time, 2.5 million years ago, one human, the other paranthrope (one of our close cousins, as its name – “next to the man” – indicates).
This discovery is essential, because until recently there were no hominid fossils dating back between three and two million years. And it was not explained why the paranthropes, or “robust Australopithecines”, had become extinct a million years ago, while the more fragile Homo genus flourished and spread throughout the planet, as we know.
In the documentary, the scientist explains that it is the way the young were raised and in particular the age at which they were weaned that made the difference.
The age of weaning
Thanks to the analysis of tooth enamel,[2] the researchers were able to show[3] that
early Homo offspring was breastfed in significant proportions until the age of around three to four years, which likely played a role in the apparition of traits that are specific to human lineage, such as the brain development. In contrast, infants of Paranthropus robustus, that became extinct around one million years ago and were a more robust species in terms of dental anatomy, as well as infants of Australopithecus africanus, stopped drinking sizeable proportions of mother milk in the course of the first months of life.[4]
Weaned late and therefore more protected and educated, Homo survived and developed his intelligence notably thanks to long breastfeeding!
Taking care of children has made humans more intelligent
This discovery is consistent with the hypothesis of Steven Piantadosi and Celeste Kidd, two American academics from the University of Rochester (New York), who suggested that the need for complex and prolonged care of children would have stimulated the intelligence of adults.
To reach this conclusion, the researchers compared different species of primates, and showed a quasi-linear link between the degree of intelligence of a species and the age of weaning of its young, from marmosets, which are only breastfed for a few months and are considered to be not very intelligent, to chimpanzees, whose young are only independent at around three to four years of age and whose intelligence is close to ours.[5]
The extreme dependence of human babies means the parents have to take care of them for several years. This allows time for both socialization and the transmission of knowledge, and has made us, as human beings, what we are.
[1] https://television.telerama.fr/tele/theatre/kromdraai-a-la-decouverte-du-premier-humain-1-193355412.php
[2] 具体的には、子供の母乳摂取量に応じたカルシウムの安定同位体の割合です。
[3] Théo Tacail, Jeremy E. Martin, Florent Arnaud-Godet, J. Francis Thackeray, Thure E. Cerling, José Braga, Vincent Balter, Calcium isotopic patterns in enamel reflect different nursing behaviors among South African early hominins, Science Advances 2019; 5(8): eaax3250.
[4] “First human ancestors breastfed for longer than contemporary relatives”, https://www.sciencedaily.com/releases/2019/08/190829115427.htm
[5] Extraordinary intelligence and the care of infants, PNAS 2016; 113(25): 6874-9.