Your belly button marks where the umbilical cord used to be
The belly button marks the area where the umbilical cord used to be attached, says Dr Christopher S. Baird, assistant professor of physics at West Texas A&M University.
When a baby is in the womb, the umbilical cord attaches to the navel at one end and your placenta – an organ that develops during pregnancy that’s attached to the uterus – at the other. The umbilical cord transports nutrients from the mother to the baby.
Once a baby is born, the umbilical cord becomes useless. The body responds to the transition by closing up the point where the umbilical cord connected to the body. The result: A belly button.
Not all mammals have a belly button
You would expect all mammals to have a belly button, but there are some exceptions. One of note: Marsupials (like kangaroos and wombats). When it comes to marsupials, the foetus is incubated for much less time, so their need for in-utero nutrition is less. After birth, they crawl up to mum’s pouch and latch on to a nipple, and do the rest of their foetal development there. Yes, your dog or cat has one – you just may not have noticed them because they’re usually smooth or flat and covered by fur.
Most are “innies”
While most belly buttons begin as outies, the majority fold in during the healing process to form innies, with only 10 per cent of people holding onto their outies through adulthood. That said, if you’re unhappy with yours, chances of it naturally switching are slim to none as an adult.