These individuals explore their environment less. They’re less social with other members of their own species. They react more skittishly to unknown stimuli. They like to play it safe. Babies with low-cortisol milk, on the other hand, explore more. They’re more social. They spend more time playing with their den mates. And when they grow up, their personalities tend to have similar features. While many things go into building an individual’s personality, at least among species we’re able to study in the lab, what’s in the milk they drink is, all on its own, a strongly predictive factor.[*14]
