* Nombrilical Cord: Navels are the result of the umbilical cord, which connects the developing fetus to the placenta.
* Placenta: The placenta is a structure found only in mammals. It provides nutrients and oxygen to the fetus and removes waste products.
* Live Birth: For mammals, this umbilical cord is a key component of live birth.
While some other animals, like sharks, have structures that resemble navels on their surface, these are actually scars from yolk sacs that were used for development in the egg.
So, humans are the only animals that have a navel as a result of the umbilical cord and placental connection of live birth.