Human Errors #2: Sinuses

After the eye, Nathan Lent looks into the “design defects” of human nasal sinuses in Human Errors. They are those huge cavities (there’s a lot of empty space in our skull) with mucus membranes. When we breathe air, it passes through these “filters” to prevent dust and germs from entering the body. In addition, they also warm and humidify the air we breathe. Of course, eventually the mucus gets saturated, at which point it is dumped into the stomach:

“(Stomach is) the safest place for the mucus, since the bacteria and viruses it contains can be dissolved and digested by the acid there.”

 

Sinus problems start when this system gets “gummed up”. At that point, the bacteria aren’t getting cleared, accumulate enough to form colonies, and in the worst cases, sometimes manage to enter the (rest of the) body.

 

So why do humans suffer more sinus problems than almost any other species? There are many reasons, and one of the important ones is that:

“The mucus drainage system is not particularly well designed.”

Specifically:

“Putting the drainage-collection point high within the sinuses is not a good idea because of this pesky thing called gravity… What kind of a plumber would put a drainpipe anywhere but at the bottom of the chamber?”

When we have a cold, the mucus thickens, the body’s mechanism struggles to push up this thicker and more-viscous-than-normal stuff to the drainage point.

 

But why is the drainage system at a higher level? Evolution has the answer. In most mammals, smell was the most important sense (ergo, the elongated snouts). But in primates, other senses became important too, and so the “snout regressed, and the nasal cavities got smushed into a more compact face”. In humans, the faces got smaller than the other primates, and the brain got bigger. Everything else in the skull had to “adjust”:

“This rearrangement produced a suboptimal design that has left us more susceptible to colds and painful sinus infections than perhaps any other animal.”