To put it simply, the navel is the scar. When a child is in the womb, with the placenta it connects the umbilical cord is a hollow long tube in which are one vein and two arteries. The arteries take the blood from baby to the placenta, where it is purified from the metabolic products of the fetus and is saturated with oxygen, nutrients, in short those that ate mom. Ago and already returned to Vienna.

After birth the umbilical cord clamp and cut (sometimes this task trust "happy" dads who on his head happily decided to attend the childbirth), leaving a portion of the umbilical cord, while holding a special pin.

After a time the umbilical cord disappears by itself (simply withers) and remains circular scar. As in the genetic code there is no information about what should be the navel, every person is unique, even among twins (by the way, on the navel-they are distinguished in the hospital).

In traditional medicine, the navel is used as a reference when separating the stomach into the visual sector. If the belly button has changed its position (for example, was a neat round hole, and began clumsily bump), then it may indicate some diseases (increased intra-abdominal pressure or enlargement of the liver, or umbilical hernia).
As for the aesthetic plan, the strong half of humanity (some) considers this part of the body is very attractive, if not more – sexy. Than willing to use girls, reinforcing this view piercing and decoration of the navel all sorts of pendants and earrings.
In some religions, the navel, the center of mass of qi energy. In Christianity regarding this on is not the first debate. In many paintings of different eras and Adam and eve are depicted what do you think? Properly, the very one with the navel. But here I do not understand them like no one gave birth to (remember Adam from clay, eve from Adam's rib).
You can argue long, one thing is clear – if not in this life then in the life in the mother's belly, the umbilical cord played a major role in actually our very existence. My opinion is that the navel, it's us as a reminder that often need to hug and tell your mom "I love you".