You have a little dimple right in the middle of your belly. Some people's poke in, some poke out, but everyone's got one. It's your belly button — the one scar every human being carries from their very first home.

Before you were born, you lived inside your mother's body for nine months. But here's the thing: you couldn't eat food or breathe air in there. Your lungs were full of fluid. Your stomach was empty. So how did you stay alive?

Your mother's body did all the work for you. She ate food, breathed air, and her blood carried oxygen and nutrients everywhere it needed to go — including to you. But your blood and her blood never actually mixed. You needed a bridge.

That bridge was the umbilical cord — a twisty, rubbery rope about as thick as your thumb, connecting you to a pancake-shaped organ called the placenta stuck to the wall of the womb. Blood flowed from your mother to the placenta, then through the cord into your belly, delivering everything you needed to grow.

For nine months, that cord was your lifeline. Every heartbeat sent food and oxygen rushing into you. Every breath your mother took kept you alive. You floated and grew and kicked, tethered to her like an astronaut on a spacewalk.

Then one day, you were born. You took your first breath. Your lungs filled with air. Your stomach was ready for milk. You didn't need the cord anymore — so a doctor clamped it in two places and snipped it right in the middle. It didn't hurt. The cord had no nerves.

A little stump stayed attached to your belly, about an inch long. Over the next week or two, it dried up, turned dark, and eventually just fell off — like a scab after a scraped knee. What was left behind was a small scar.

That scar is your belly button. It's the place where you were once connected to the person who grew you. Every time you see it, you're looking at the mark of your very first address — and the door you came through to get here.