Baby monkey get signals from their mothers' breast milk that help shape both their behavior and their temperament, a new study found.
Katie Hinde led a team from UC Davis and The Smithsonian Institution that looked at variations in the breast milk of rhesus macaque monkeys living in the outdoor enclosure at the California National Primate Research Center.
The experiment was based on the fact that mothers who are heavier and have raised previous offspring tend to produce more nutritious breast milk than new mothers or mothers who weigh less. This is true even though these monkey are all fed the same diet and live together in the same environment.
After analyzing the mothers' breast milk, the researchers looked at the behavior of their babies when they were three or four months old. According to Science Daily:
At 3 to 4 months old, each infant was temporarily separated from its
mother and assessed according to its behavior and temperament. The
study found that infants whose mothers had higher levels of milk energy
soon after their birth coped more effectively (moved around more,
explored more, ate and drank) and showed greater confidence (were more
playful, curious and active). Infants whose mothers had lower milk
energy had lower activity levels and were less confident when separated
from their mother. Mothers and infants were reunited immediately after
The scientists think that cues from the breast milk may discourage behaviors that are risky in times of scarcity. For example, if food is scarce, a young monkey shouldn't waste energy playing around.
By the way, there's pleny of reason to assume this would hold true for humans. In fact, rhesus monkeys are often used in research on human diseases and drugs.
We know that a human baby's brain development is strongly influenced by experiences after birth. It certainly seems like nutritional cues could play a bigger role than we normally think.