Difficulty Breastfeeding

 Breastfeeding (i.e., sucking the mammary gland to ingest milk) is a defining feature of mammalian infant care. Human mother-infant dyads are unique from other primates with regard to the difficulty engaging in this practice. Unlike most other mammals that breastfeed their young fairly automatically, primate mothers need support and teaching in order to achieve breastfeeding success. Humans are not the only primates that need to be taught how to breastfeed their offspring, yet humans require more learning than our closest primate relatives. However, the learning necessary for successful lactation in human mothers seems to be greater in comparison with other primates.

There are multiple potential explanations for this human difference in breastfeeding difficulty. A human neonate can use smell and reflexive motor movements to instinctually reach the mother’s breast after birth, but cannot do this successfully unless placed on the mother’s chest. This relative immaturity of motor development in comparison with other primates seems to be an evolutionary tradeoff for the benefits of an extended period of development. Human infants also have innate reflexes to gape their mouth open when something is near their mouth and to suck when something is in their mouth. However, successfully withdrawing enough milk from the breast requires proper positioning of the breast in the infant’s mouth (i.e., the nipple at the very back of the mouth), which is difficult for human infants without direct help from the mother. If the mother lacks knowledge of how to help her infant engage in this proper technique, the infant will not get enough milk.

Even with proper education and support, many human mothers cease breastfeeding early or choose not to breastfeed their infant for a variety of social, psychological, and biological complications. Another human-unique complication is sucking technique. Though other mammals use negative suction to extract milk from the breast, human infants engage pressure on the areola – using an intro-oral vacuum in combination with a lowering of their tongue – to remove milk from the breast. This sucking technique is novel in the mammalian world, which likely contributes to the difficulty of human mother-infant dyads in effectively breastfeeding. Another human challenge to successful lactation is the psychological condition of perceived insufficient milk supply (PIM), which is when mothers falsely think they don’t have enough milk for their infant and is the explanation given by 35% of mothers who discontinue breastfeeding. This is not solely a Western phenomenon, as studies have reported equivalent prevalence of cases of PIM in Mexico, Hong Kong, Thailand, and Turkey. More broadly, social support (i.e., from partners, parents, friends, and communities) is also critical to increasing the likelihood of breastfeeding success. However, this is most problematic in the Western world, where the availability and convenience of infant formula provides a simple and widely-accepted alternative to making the effort to learn proper breastfeeding techniques.

Lactation was evolutionarily beneficial by decreasing risk of infant mortality while reinforcing altriciality and the mother-infant bond, so it is unclear why humans evolved to have such a challenging time breastfeeding offspring. One theory is that the learning required to achieve breastfeeding success was a tradeoff between having a very successful innate sucking mechanism in infancy versus having a more flexible, adaptive brain. Breastfeeding was also clearly related to the increased importance of social bonds in human history, as social learning and support from other mothers seems to have been necessary for infant survival via breastfeeding competency. Another potential evolutionary mechanism leading to the unexplained difficulty of human lactation is sexual selection pressure. Human breasts are significantly larger than those of other primates, and they serve as a cue to fertility and sexual desirability. Human males reliably look longest at a woman’s breasts when viewing a nude woman. The pressure from sexual selection may have favored larger breasts despite their inefficiency for nursing. In modern humans, breast size and breastfeeding success are not related, as breast size is attributed to fat pads rather than mammary gland branching.