I’ve been a huge fan of pop science author Mary Roach’s work ever since “Stiff: The Curious Lives of Human Cadavers“, her entertaining book on how we use and dispose of corpses. Her latest book, Gulp: Adventures on the Alimentary Canal (non-affilate link here), is a similar quirky but informative work that focuses on the human digestive system, from the point at which food lands on your tongue to the long trip it takes to the toilet.

Her inspiration for this topic? The “gross” process of digestion has, in Roach’s opinion, relegated it to obscurity:

Feeding, and even more so its unsavory correlates, are as much taboos as mating and death. The taboos have worked in my favor. The alimentary recesses hide a lode of unusual stories, mostly unmined. Authors have profiled the brain, the heart, the eyes, the skin, the penis and the female geography, even the hair, but never the gut. The pie hole and the feed chute are mine. Like a bite of something yummy, you will begin at one end and make your way to the other.

The book appeals to a broad audience, but I think the engineer in me especially appreciates Roach’s curiosity. Eating…and everything that happens after it…is such a routine, mundane, yet hidden and essential process that we don’t perceive it as being complex or interesting, just as we generally ignore the amazingly complex sewage systems that make our cities livable. The best engineered works almost always involve details and logistics we don’t care to think about.

An example from Roach’s book: the flammability of farts. Though great material for YouTube today, this was apparently a serious concern in space exploration. In NASA’s early days, Roach writes, they were so worried about the build-up of human gas in the sealed space capsules that it was suggested that astronauts should be selected only from “that part of our population producing little or no methane or hydrogen.”

Roach’s book covers more than the waste-part of human eating, but I think her most memorable passages come at the end. First, here’s an engineering joke that seems to be told to every incoming freshman engineering class:

An electrical, a mechanical and a civil engineer all sat down one day to try and decide of which of their faculties god must be to design the human body.

The electrical engineer says god must be an electrical engineer, for you only have to look at the complex nervous system powered be electrical impulses.

The mechanical engineer was sure that god must be a mechanical engineer, for the advanced mechanical systems, the heart a pump, the veins pipes and the tendons and muscles an advanced pulley system.

Finally after hearing the civil engineers arguments, both the mechanical and electrical engineer both agreed that god must be a civil engineer, for who else would run a sewer system through a recreational area!

The joke is meant at the expense civy engineer’s lack of aesthetics, but author Mary Roach presents an amusing rebuttal, of sorts; it’s not careless planning, but a bonafide miracle of engineering:

Any discussion of the sexuality of the digestive tract must inevitably touch on the anus. Anal tissue is among the most densely enervated on the human body. It has to be. It requires a lot of information to do its job. The anus has to be able to tell what’s knocking at its door: Is it solid, liquid, or gas? And then selectively release either all of it or one part of it. The consequences of a misread are dire. As Mike Jones put it, “You don’t want to choose poorly.”

People who understand anatomy are often cowed by the feats of the lowly anus. “Think of it,” said Robert Rosenbluth, a physician whose acquaintance I made at the start of this book. “No engineer could design something as multifunctional and fine-tuned as an anus.”

“To call someone an asshole is really bragging him up.”

-via Roach, Mary: Gulp: Adventures on the Alimentary Canal (pp. 216-217). W. W. Norton & Company. Kindle Edition.