We've always assumed our navels are just for piercing, but Aki Sinkkonen has a new theory on the belly button: he believes that they served the evolutionary purpose of signaling fertility to potential mates.
In an article published in the latest issue of The FASEB Journal, Sinkkonen proposes that the "symmetry, shape, and position of umbilicus can be used to estimate the reproductive potential of fertile females, including risks of certain genetically and maternally inherited fetal anomalies." He found that people have very clear preferences for their belly buttons, preferring those that are only slightly indented (so never outies!), t-shaped or oval, and a little hooded. Sinkkonen suggests that abnormal bellybuttons may indicate a risk of several fetal abnormalities. However, in case you are feeling bad about your outie, or heavily-hooded navel, Sinkkonen says: "Don't worry. Nobody's perfect except Angelina Jolie." [LiveScience]