According to a recent study, female mammals who share their mother's milk with other young than their own enjoy more biological advantages. But what does that really mean?
Breast milk is quite often at the heart of some research. In 2020, for example, a company had created a new generation baby milk closer to breast milk. Other studies have made it possible to discover a new benefit of breast milk or to warn against its use as a doping product. More recently, a duo of biological anthropologists from New York University (United States) carried out work presenting the biological advantages of female mammals ensuring that their mother's milk is shared with their young, but also those of other females.
The work published in the journal PNAS on March 1, 2022 concerned approximately 1,800 species of mammals including primates and rodents. Paola Cerrito, co-author of the study, said the idea for such research came from her Italian grandmother. The latter had survived the Second World War and had explained to her granddaughter how young mothers of the time helped each other in breastfeeding. Indeed, some mothers breastfed newborns that were not their own. This practice had appeared at a time when very many people were suffering from malnutrition.
The duo of scientists developed models aimed at evaluating different types of parental assistance in terms of their reproductive performance in wild and domestic mammals. According to the results, allolactation (another name for milk sharing) allows better fertility in females nursing other young than their own. However, this fertility benefit is greater than that conferred by natural selection and especially domestication. Concretely, females sharing their milk generally have larger litters and thus give birth to more babies each year (+20% on average).
Domestication allows a better supply of energy resources compared to the wild state. On the other hand, the increase in reproductive capacities is limited, because lactation requires considerable efforts from a metabolic point of view. However, breastfeeding is an independent energy supplement maternal metabolism. Thus, the physiological constraint of metabolism is circumvented, which allows reproductive capacities to experience an increase.
According to the researchers, their work also provides an opportunity to better understand the biological benefits of nurse bees in humans. They claim that their results show a maximization of total reproductive output. In other words, allobreastfeeding allows the survival of more newborns.
