In 2008, evolutionary anthropologist Katie Hinde began studying breast milk from rhesus macaque mothers. What started as a routine study turned into a groundbreaking discovery. She found that mothers raising sons produced milk richer in fat and protein, while those raising daughters had different nutrient balances. This led Katie to a radical conclusion: milk is not just nutrition—it’s information.
Her research revealed that milk shapes behavior, not just growth. For instance, first-time mothers produced milk with higher levels of cortisol, influencing their babies to grow faster but also become more anxious. Katie also discovered that milk changes based on the baby’s immune needs. When a baby is sick, the mother’s milk quickly adapts by producing more white blood cells and targeted antibodies.
Katie’s work, which challenged the scientific consensus, was largely ignored. She launched a blog, Mammals Suck Milk, to spark discussions, and her findings, including that every mother’s...