Well fret no more - I have an explanation for the belly button.
I have concluded (after many hours of navel gazing) that the belly button is a one-way valve. It is a safety release for when you burp and fart at the same time. Without it when you expelled gas from both ends the vacuum created in your intestines would be so great that you would implode.
This also explains why there is a build up of belly fluff found in most navels - a natural air filter!
Hope this helps clear things up - now you can move on with your lives.