A groundbreaking study reveals that female mammals sharing breast milk with non-offspring gain significant reproductive advantages. Here's what the science shows.
Breast milk remains a focal point in scientific research. In 2020, innovations brought formula closer to its composition. Other studies have uncovered new perks or cautioned against misuse, like doping. Recently, biological anthropologists from New York University analyzed biological advantages for female mammals who share milk with their own and others' young.
Published in PNAS on March 1, 2022, the study examined about 1,800 mammal species, including primates and rodents. Co-author Paola Cerrito drew inspiration from her Italian grandmother, a World War II survivor. She recounted how young mothers supported each other by nursing non-biological infants amid widespread malnutrition.
The researchers modeled parental care strategies to assess reproductive performance in wild and domesticated mammals. Results show allolactation—milk sharing—improves fertility more than natural selection or domestication alone. Females practicing it produce larger litters, averaging 20% more offspring annually.
While domestication provides better nutrition than the wild, lactation's metabolic demands limit gains. Milk sharing acts as an independent energy boost to maternal metabolism, bypassing these constraints and elevating reproductive output.
This research sheds light on benefits for human wet nurses, demonstrating maximized total reproduction—more newborns survive through communal nursing.
