3 years of breastfeeding were compelled by the leading causes of infant mortality in ancestral settings—infection and malnutrition-related disease; lactation-based caregiving gave lactation-based cohesion, with fitness payoffs for infants

Attachment and Caregiving in the Mother–Infant Dyad: Evolutionary Developmental Psychology Models of their Origins in the Environment of Evolutionary Adaptedness. Sybil L. Hart. Evolutionary Perspectives on Infancy pp 135-160, January 1 2022. https://link.springer.com/chapter/10.1007/978-3-030-76000-7_7

Abstract: This chapter offers evolutionary developmental psychology models of caregiving and attachment as species-wide features of infant–maternal relationships. We explain that 3 years of breastfeeding were compelled by the leading causes of infant mortality in ancestral settings—infection and malnutrition-related disease—and discuss how it underpinned lactation-based caregiving and a biobehavioral bond, lactation-based cohesion, with fitness payoffs for infants: (1) protection against malnutrition and morbidity; (2) preservation of the inter-birth interval (IBI) as a haven against competition with a newborn sibling; and (3) psychological benefits of steady and enduring exposure to a profoundly satisfying manner of proximal contact with a caregiver. We theorize that lactation-based caregiving and cohesion satisfied infants’ physical and psychological needs, and in doing so laid the foundation of a psychological adaptation, child-to-mother attachment, an affectional bond able to withstand being untethered to lactation by infants’ third year. The timing of the transition from lactation-based cohesion to attachment coincided with attenuated dependence on breast milk due to maturation of infants’ digestive and immune systems, and with the eruption of infants’ molar teeth, which prompted mothers to bring breastfeeding to conclusion. At this juncture, mothers transitioned to caring for weanlings (rather than nurslings), which meant an end to maternal caregiving being upheld by biobehavioral features of lactation. We argue that absent such support, the costliness of caregiving of weanlings compelled an adapted psychological mechanism, mother-to-child attachment, defined as an affectional bond between ancestral mothers and their former nurslings that was anchored in 3 years of lactation-based caregiving and cohesion.

Keywords: Lactation-based cohesion Lactation-based caregiving Child-to-mother attachment Mother-to-child attachment Breastfeeding Lactation Breast milk Kwashiorkor