We have a belly button because this was the place that used to attach us to our mothers before we were born. We were attached by a thing called the ‘umbilical cord’ and this provided us with food and oxygen while we were developing in our mum’s tummies. When babies are born, you have to cut the umbilical cord to separate them from their mothers. The belly button forms in the place on the baby where the umbilical cord used to be. All warm blooded animals have them.