Why do we have belly buttons?
For grown-ups: the science
A belly button is the healed spot where the umbilical cord connected you to the placenta before you were born.
The umbilicus is the scar left after the umbilical cord is clamped and separated following birth. During pregnancy, the cord connects the fetus to the placenta, which exchanges oxygen, nutrients, and waste products between fetal and maternal blood without the two blood supplies normally mixing directly. Belly button shape varies because of healing and anatomy, not because of how the cord was cut.
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Transcript
Look at the little spot in the middle of your tummy. Why do we all have a belly button?
Before birth, a cord joins the baby to the placenta in the pregnant parent's uterus. It brings oxygen and food to the baby.
After birth, the cord is cut, and the small piece on the baby dries and falls off. The healed spot is the belly button.
A belly button is a small scar from where the cord was connected. It is a reminder of how you grew before birth.
So your belly button marks where your birth cord was connected. It does not need to do that job anymore.