I sometimes quiz my son about our particular advantage in the animal kingdom. Can we fly? No. Can we change colors to camoflauge ourselves? Are we super fast? No. What's our advantage in the animal world? It's our brains! (Yes, opposable thumbs also help. Can't text without those.)
A new study finds that in humans, as well as other mammals, the longer gestation and duration of breastfeeding, the bigger brain a species has.
To be clear, they aren't suggesting that an individual baby gets a bigger brain as a result of breastfeeding, but that the bigger investment a species makes in in utero and nursing is reflected in bigger brain size. Put another way, we are big brained mammals, and developing that big brain requires a long gestation and nursing phase.
The Belfast Telegraph reports:
The anthropologists from Queen’s and Durham’s Evolutionary Anthropology Research Group analysed statistical evidence on brain and body size, maternal investment, and life history variables in mammals, including gorillas, elephants and whales.
They found that brain size relative to body size was most closely linked to maternal investment — the amount of time a mother spends carrying her offspring in pregnancy and how long she continues to breastfeed.
And our milk is reflective of the importance of brain development. Compared to other mammals, our milk is low in protein and fat, but high in carbohydrates including oligosaccharides - a component which includes sialic acid and galactose, which are essential for brain development. Dr. Sears describes this function:
Each species' milk has specific qualities that insure the survival of the young in a particular environment. This principle is known as the biological specificity of milk. Mother seals, for example, make a high-fat milk because baby seals need lots of body fat to survive in cold water. Since brain development is crucial to the survival of humans, human milk provides nutrients for rapid brain growth.
This high-carb, low fat/protein diet is also consistent with the idea that we are "carry mammals." As I posted a while back, this idea is described in Breastfeeding Made Simple:
The carry animals are the most immature at birth, need the warmth of the mother's body, and are carried constantly. Their milk has low levels of fat and protein, and they are fed often around the clock. Humans are most definitely carry mammals. Human milk has the lowest fat and protein of all mammalian milks. That, and our immaturity at birth, means human infants need to feed often and are meant to be carried and held.
And of course, in addition to being protected in this vulnerable state, babies who are kept close to adults have the opportunity to grow and learn and develop their brains.
For more on the nursing patterns of different mammals, check out this podcast interview I did with Dia Michels!