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 Christopher S. Baird, PhD, assistant professor of physics at West Texas A&M University in Canyon, TX.
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 fetus is incubated for much less time, so their need for in-utero nutrition is less. After birth, they crawl up to mom’s pouch and latch on to a nipple, and do the rest of their fetal 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.
It’s teeming with bacteria
Despite its proximity to you, the belly button goes largely ignored, unless you adorn it with body jewelry or are fond of midriffs. But it’s actually one of several body parts that accumulate weird gunk. A 2012 study in the journal PLOS One found that there are at least 67 groups of bacteria organisms found in each belly button, with six different types making up the majority in more than 80 per cent of people.
Belly button plastic surgery is a big deal
Not everyone is keen on their belly button, which is why belly button plastic surgery is kind of a big deal. (The procedure is called an umbilicoplasty.) It turns out that we have a general preference for navel aesthetics. In one study in 2017 in Plastic and Reconstructive Surgery, an oval-shaped belly button was deemed the most attractive.