How babies are born knowing the difference between day and night

AI Summary

A developing fetus can receive maternal signals that help distinguish day from night before birth. Melatonin, which is mainly released at night, can cross the placenta, an organ that supplies the fetus with oxygen and nutrients.

Before a baby sees its first sunrise, it is already receiving signals about day and night. Melatonin, a hormone released mainly at night, can pass from the mother through the placenta. The placenta supplies the developing fetus with oxygen and nutrients.