When parents hear their baby’s cries through the monitor in the middle of the night, they run through a mental checklist of all the possible reasons. Maybe he’s cold. Or hungry. Or needs a clean diaper. But a new study suggests a far more nefarious reason: to prevent mom and dad from making another baby.
An evolutionary biologist at Harvard named David Haig describes the theory in Evolution, Medicine, and Public Health. When a baby screams to be breastfed in the middle of the night, he’s actually preventing mom from getting pregnant. It’s essentially sibling rivalry before the other sibling exists — babies don’t want to share mom and dad with anyone.