The university of life

The belly button

Since one of the main goals of the University of Life is to educate the people we were really interested in the Lecture by Scott Gilbert we recently witnessed in which he proposed to use Evo-Devo (evolution and development) to teach about evolution instead of population biology. Although we are certainly not an expert in the field of Evo-Devo, we want to put forward a case that might be relate to some degree to this field of research. Today's topic will be the navel or belly-button.

There have been many functional studies of the belly button at the UOL and other independent research institutes. And all studies reached a similar conclusion. But first we would like to clarify the nature of the belly button. The navel is a depression into the abdomen usually centrally located. This prominent central location raised the suspicion that the belly button is of great importance to normal functioning of the average human being. The first indication of the function came from many independent reports by medical personnel all over the world stating the occurrence of a strange fluffy substance in the navel. This substance was subsequently named navel fluff.

Researchers traced the origin of the fluff and found that a fluff particle can be located anywhere on the belly to start with, but always ends up in the belly button. The mechanism of fluff collection is not quite clear yet. Some claim that the constant action of clothes moving over the belly causes a random migration of the fluff, and once it hits the belly button it gets trapped. Others claim that their computer models predict that this passive migration is not enough and an additional active process is required. Preliminary studies report the presence of a large number of tiny hairs on the belly distributed in a specific pattern. All hairs point towards the belly button and guide the migration of fluff particles. A controversial study even reported that these hairs actively move fluff, by slowly moving back and forth. Although this work has been received with a lot of skepticism, subsequent studies reported the presence of tiny muscles attached to most hairs.

There might be some controversy about the nature of the mechanism, be it active or passive, all agree that the function of the belly button is to collect navel fluff. Without this collection device the fluff would soon gather in large quantities covering the entire abdomen (as has been shown by experimental studies covering up the belly button). These fluff deposits soon attract a myriad of parasites and forms an obvious health hazard.

And this is how evolution works. Humans started wearing simple clothes about 100.000 years ago. With clothes fluff got introduced onto the body. Survival of the fittest subsequently guaranteed the survival of the individuals with the most efficient means of removing fluff. And the belly button was shaped by evolution. Strangely enough the function of the navel hasn't always been to collect fluff. The belly button is also a classic example of a structure whose function has been reshaped by evolution into an entirely different one.

By looking at early development we get a glimpse of the primitive function of the belly button. Before a human baby is actually born the belly button is actually not present in the shape that is familiar to all of us. Where the belly button should be there is a cord of tissue that connect the fetus to the placenta. In the medical world this structure is also known as the umbilical cord. Once the baby is born this umbilical cord is usually cut away since it serves no purpose and the glorious development of the navel commences.

Comparative studies showed the presence of the umbilical cord in all mammals. It is suspected that in at least primitive mammals the placenta acts as an exchange station for nutrients, oxygen and waste products between mother and fetus. The umbilical cord serves as the hose connecting placenta and fetus. It is not clear if this function is still needed in human development. We do know that this ancient structure, the navel, once only served as a connection point between umbilical cord and baby. In modern man, it gained an all-new and important function, the collection of navel fluff. Evolution did this by modifying the development of the navel structure, which resulted in an almost perfect collection device for fluff. Evolution never ceases to amaze us.


Professor at the UOL

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