Umbilicus as a fitness signal in humans.

Typically, mammalian umbilical cord forms a tiny, stable, and asymmetrical scar. In contrast, humans have a clearly visible umbilicus that changes with age and nutrients gathered. Based on this, I propose that umbilicus, together with the surrounding skin area, is an honest signal of individual vigour. More precisely, I suggest 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. The idea is supported by a comparative study where symmetrical t-shaped and oval-shaped umbilici of fertile females were considered the most attractive. Further support comes from observations that abnormal velocity of umbilical cord has been associated with fetal brain development, diabetes, and other fitness-related properties with a strong genetically or maternally inherited component. In addition, umbilicus and the umbilical skin area may reveal nutrimental competitive ability, and need for social care in small children and pregnant females. The novel hypothesis explains why umbilicus has aesthetic value, and why umbilicus has had a distinctive role in different cultures. If further research confirms the signalling hypothesis, female umbilici may be routinely measured to detect risk pregnancies of several fetal abnormalities.