Primate milk: Proximate mechanisms and ultimate perspectives

Abstract

To understand the evolutionary forces that have shaped primate lactation strategies, it is important to understand the proximate mechanisms of milk synthesis and their ecological and phylogenetic contexts. The lactation strategy of a species has four interrelated dimensions: the frequency and duration of nursing bouts, the period of lactation until weaning, the number and sex ratio of infants that a mother rears simultaneously, and the composition and yield of the milk that mothers synthesize. Milk synthesis, arguably the most physiologically costly component of rearing infants, remains the least studied. Energy transfer becomes energetically less efficient, transitioning from placental support to milk synthesis just as the energy requirements for infant growth, development, and behavioral activity substantially increase. Here we review primate lactation biology and milk synthesis, integrating studies from anthropology, biology, nutrition, animal science, immunology, and biochemistry, to identify the derived and ancestral features of primate milks and enhance our understanding of primate life history.

Holsteins Favor Heifers, Not Bulls: Biased Milk Production Programmed during Pregnancy as a Function of Fetal Sex

“…Milk synthesis is unlikely to be at the maternal optimum because of parent-offspring conflict [32][33]. Rather milk reflects a complex physiological and behavioral negotiation between the mother and offspring [34][35]. Functional development of the mammary gland initially occurs during pregnancy and is orchestrated by maternal and placental hormones, particularly placental lactogen, estrogen, and progesterone [36][37][38].…”

Imprinting, latchment and displacement: a mini review of early instinctual behaviour in newborn infants influencing breastfeeding success

“…Evolutionary success requires close maternal contact and frequent breastfeeds to provide nutrition for the promotion of brain metabolism and optimal growth of myelinated white matter 39, 40.…”

Allomaternal Nursing in Humans

“…Hewlett and Winn acknowledge that not all instances of infants at the breast are actual suckling, but the rates of pacification versus milk intake remain unclear. Milk intake varies between infants and is largely controlled by milk supply and demand (Hinde and Milligan 2011); the amount of milk produced by a mother or allomother is not likely to be representative of the amount of milk that an infant ingests, making estimates of energy consumption difficult to determine (Miller et al 2013). Among human biologists studying lactation, behavioral observations of breast-feeding are the least desirable measurement of infant milk intake because they are notoriously unreliable (Scanlon et al 2002).…”

“…Hundreds of bioactive constituents are present in milk. These include fats, carbohydrates, proteins, minerals, vitamins, hormones, immunofactors, and water (Hinde and Milligan 2011), all of which vary among mothers and are therefore likely to vary among allomothers as well. As such, allomaternal milk in many cases may be a mismatch with mother's milk.…”

“…Allonursing raises questions in addition to donor interests. Lactation is the most intimate maternal-offspring link postpartum, influencing a range of outcomes across the life span (Hinde and Milligan 2011;Lanigan and Singhal 2009), and attendant behaviors produce epigenetic and intergenerational modifications (Champagne 2011;Meaney and Szyf 2005.…”