Scarred for Life
Belly buttons aren’t evolutionary leftovers. Technically, belly buttons are scars. They’re the remnants of the umbilical cord and placenta, which connect a baby to its mother while in utero. Once the baby is born, the umbilical cord is severed and tied off, scar tissue forms in the place where the umbilical cord attached to the abdominal wall, leaving us with the strange formation we know as a belly button.
All mammals have belly buttons, from mice to whales, because all mammals give birth to live young. Even animals born in litters, like dogs and cats, have their own placenta, so they have a belly button, too. Rather than being the noticeable marks that they are on humans, animal navels tend to be smoother and flatter, often nothing more than a thin line. Plus, the fact that they’re covered with fur tends to make them harder to see.
Are You In or Out?
About 90 percent of humans have concave belly buttons, or “innies.” In concave belly buttons, the scar tissue develops inward, growing toward the abdominal wall. Convex navels, or “outies,” protrude away from the stomach, with extra scar tissue causing them to stick out. Infants start life as outies and in the first few months of life, the remnants of the umbilical cord shrivel and fall off, forming the navel the child will have the rest of her life. No one knows why some navels become concave and some become convex. It’s not a genetic trait; it’s simply random chance. We do know a few things about them though—they have nothing to do with the skill of the doctor severing the placenta or how the cord is cut, since that’s done several inches away from the body. A person’s belly button also has no bearing on his health or vitality.
Sometimes, an outie is not really an outie. A protruding navel can actually signal an umbilical hernia, which is not uncommon in infants. If the abdominal muscles don’t seal off properly after the umbilical cord is cut, part of the intestine can force its way through the opening. Most umbilical hernias close up on their own by about age one, although some take a bit longer to heal, and could potentially require minor surgery. There’s an easy way to tell whether a baby’s protruding navel is a hernia or just a standard-issue outie: hernias only protrude when a baby cries and normal outie navels are always protruded.
During pregnancy, the pressure from the growing fetus can cause a woman’s innie to pop out and become an outie, but after childbirth, most women find that their navels return to their original configuration. Not all women experience changes with their navels, but it’s a perfectly normal occurrence during pregnancy. Unfortunately, a popped-out navel isn’t like the button on a turkey, and doesn’t mean the baby is ready to be born.