Signaling Between Mother and Infant During Lactation: Evolutionary, Anthropological, Biological, and Practical Considerations

Lactation is an ancient process that long predated the emergence of mammals or placentation. It most likely evolved primarily as a source of fluid and immune factors in our egg-laying ancestors, with a nutritional role developing later. Many nutritional components of milk evolved from immune components. Milk provides young mammals with nutrition and immune protection, but also allows “signaling” between mother and offspring during critical early developmental phases of life. Lactation allowed mammals to shape their offspring’s growth and development over a much longer period than was possible in egg-laying animals.

Lactation presents a wide range of signaling options. The mother can exert influence by providing or limiting access to the breast, via altered volume and nutrient content of the milk, and via myriad non-nutritive components, including hormones, microbes, oligosaccharides, microRNAs, and cells (eg, milk stem cells). The infant can signal to the mother by vocalization, feeding demands, and non-nutritive suckling. Defining the role of these signals is complicated, especially in humans, by the complex inter-relationships between factors and by methodological issues with milk sampling, processing, and assays. An experimental approach, including standardized protocols for milk sampling and analysis, is therefore preferable to investigate causality.

Primate lactation is characterized by long periods of lactation with dilute, low-fat, and low-protein milk, which has the advantage of spreading the energy cost of investment and prolonging the potential signaling period. However, it also creates greater potential for conflict between mother and infant, since lactation is energetically expensive. The mother needs to invest in all her offspring and benefits from early weaning and another pregnancy, while the infant prioritizes itself over its siblings and benefits from longer breastfeeding. Lactation is therefore not a “one-way” process, and conflict should be anticipated: lowering the tension between mother and infant may provide benefits for both parties. Applying an anthropological perspective, combined with improved understanding of signaling mechanisms, may thus help to explain some breastfeeding problems and define solutions.

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Speaker Bio - Mary Fewtrell, MD, BM BCh, FRCPCH

Dr. Mary Fewtrell received her medical degree from the University of Oxford and her MD from the University of Cambridge. She is currently Professor of Pediatric Nutrition and Honorary Consultant Pediatrician at University College London Great Ormond Street Institute of Child Health. In addition to her training in medicine and pediatrics, she has spent over 20 years researching infant and child nutrition.

Dr. Fewtrell’s research interests include the programming of health outcomes by early nutrition and growth, investigated in randomized nutritional intervention trials in both term and preterm infants, with longterm follow-up; and practical aspects of infant nutrition, with studies on breastfeeding, breast milk expression, and complementary feeding. She also collaborates with Professor Jonathan Wells to investigate both biologic and anthropologic aspects of infant feeding. Dr. Fewtrell is well published, having authored over 200 manuscripts, congress abstracts, and book chapters. She is the Clinical Lead for Nutrition at the Royal College of Paediatrics & Child Health UK, and chairs the Committee on Nutrition of the European Society of Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN).