Evolution of mammals: lactation helps mothers to cope with unreliable food supplies

Abstract

Lactation is a ubiquitous feature of mammalian reproduction. Because lactating females can draw on their nutrient reserves for milk production, it offers mothers and their dependent young independence from fluctuations in their food supplies. However, converting food to reserves and milk is relatively inefficient at delivering nutrients to offspring. We use dynamic programming to contrast the performance of mothers that provision dependent, refuge-bound offspring optimally from their nutrient reserves with otherwise equivalent mothers that do so directly from the food they find. In this way, we demonstrate formally that the selective advantage to lactating mothers, who can provision-at a cost-without having found food recently, can be substantial with uncertain food supplies and few opportunities for future reproduction under a wide range of circumstances. Hence, it is likely that unreliability associated with the lifestyles of the small, primitive mammal-like reptiles that evolved extended maternal care, selected for fully-developed milk production and consumption, prompting the evolution of true mammals. Moreover, this work suggests that selection for coping with unreliable food access during provisioning may underlie key life-history differences between birds and mammals because the mass constraints imposed by flight restrict the level of reserves that mothers can carry and provision from.

Does breastfeeding prevent the metabolic syndrome, or does the metabolic syndrome prevent breastfeeding?

“…This concept is consistent with evolutionary models suggesting that lactation evolved to allow mammals to nourish their young in the setting of unreliable food supplies. 27 Animal models support a causal association between lactation and retained fat stores: in a murine model, dams who did not lactate had greater visceral, but not subcutaneous fat stores at 2 months postpartum than dams who lactated. 28 …”

The biology of the colonizing ape

“…In the absence of specialized physiology, behavior takes on two functions in niche construction. First, behavior may act on the niche to make it more amenable, and hence fit it to the organism, e.g., mammalian mothers buffering external energy perturbations through lactation (Dall and Boyd, 2004). Second, through behavior organisms may converge on an optimum mode of exploiting the niche, and hence fit the organism to the niche.…”

Effect of lactation on maternal postpartum cardiac function and adiposity: a murine model

“…33 During pregnancy, dramatic changes occur in a woman’s metabolism as she accommodates the demands of “metabolizing for two.” 36 These well-described increases in visceral fat, insulin production, insulin resistance, and circulating lipid levels both support the developing fetus and allow accumulation of energy stores for lactation. 37–38 However, if no lactation occurs, maternal metabolism does not return to prepregnancy state and results in a negative impact on the mother’s health. Our study is a first step towards providing evidence for the “reset hypothesis”.…”