Human navel gazing probably started with the Neanderthals 50,000 years ago and hasn’t stopped since. Our belly button does not heal over because there is nothing between it and our stomach except a few thin layers of skin.

The belly button is merely scar tissue of the umbilical cord where the cord has detached following birth. It is of no medical significance. Therefore, medical and anatomy texts pay it little or no attention.

Nevertheless, any animal that has been nourished in the womb must have a belly button, although it may not always be easily seen. According to Dr Edward Feldman of the School of Veterinary Medicine at the University of California at Davis, "the scarring may be less obvious in some animals than in others, especially if it is covered by fur".

Where does belly button fuzz come from?

Belly button fuzz (or lint) comes from the clothes you wear. Some fabrics shed more than others. Some shapes of belly buttons are better collectors. A hairy belly button will collect fuzz better than a hairless one.

What is behind my belly button?

According to the punch line of an old joke: "If you unscrew your belly button, your bottom falls off." In reality, the umbilical vein comes from the afterbirth or placenta, which carries blood enriched with oxygen and nutrients to the developing baby.

The umbilical vein runs from the navel to the fetal liver and through a bypass vessel (the ducted venosus) to the fetal heart. After birth, the umbilical vein remains open for a time, but soon afterwards it closes and shrivels up to become a fibrous cord. It crosses the abdominal cavity in a fold of the abdominal wall lining forming the round ligament (the ligamentum teres). Sometimes things don't close as they should and an umbilical hernia develops.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au

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