Human Errors; Nathan Lents; 2018; Mariner Books; 216 pages, index

The errors referred to are design flaws in ourselves. I have always found this topic interesting. We think of ourselves as the peak of creation on Earth, but this is far from the truth when the details are examined. We are not the best at anything except thinking. All of our other traits speak more to a humanity being a jack of all trades, rather than being especially good at anything in particular.

Some of the issues discussed were familiar to me. The most common example of a design flaw is the human eye. It has two problems: myopia and wiring. Many of us are near sighted because our eyes are not the right shape. But more interesting is the wiring of the eye. We have our photo receptors at the back of the retina. In other words, the light we see must punch its way through a cell to get the receptors on the other side, a process that introduces distortions and dimming of the light. In addition, the wiring is also on the wrong (front) side, again blocking the light. All the wiring comes together at one place and then plunges through the retina to get to the optic nerve. This results in our famous blind spot. At some point in our history, nature flipped a coin on eye design when the design chosen did not matter. Then we evolved and discovered our mistake. Mollusk eyes do not have this flaw. Evolution can develop very complex structures. It is very good at that. But when it makes a mistake, it has no capacity to undo the error. Rather, it introduces workarounds or just tolerates the inconvenience, as long as it does not hamper reproduction.

Our hands and feet are full of useless bones that now just cause trouble. Our knees are very susceptible to injury, as any athlete who has blown his ACL will tell you. Our spine is designed for a creature with four walking legs. It started to change when we became knuckle walkers, but back aches are common, and for some, debilitating. The shape of our spine is a kludge stacked on two more kludges. Our air hole and our food hole are side by side, making choking to death possible. We breath in and out through the same hole. This is very inefficient in that stale and fresh air mix all the time. This is called tidal breathing. Think of breathing exclusively through a hose. If the hose is more than a few feet long, you will suffocate. Birds do not have this problem, which allows them to maintain a much faster metabolism. Beating wings is hard work that requires gobs of oxygen. Our brains and hearts are well protected, but one good punch to the throat and you will die. Our sinuses too have not caught up with upright walking. They now drain up, which causes blockages, running noses,  and infections.

But my favorite example is the RLN (Recurrent Laryngeal Nerve). When we were fish, our hearts, lungs (gills) and brain were all up front in the head. The RLN, which now controls the voice box in us, had a short trip to make from  the brain and it did so by running past the heart. As tetrapods evolved (we are all tetrapods), the heart and lungs moved away from the head and we developed necks. In humans, as in all tetrapods, the RLN branches off the vagus nerve, loops around the aorta, and goes back up to the voice box.  This makes the nerve many times longer than it needs to be, and this is the kind of design flaw evolution cannot fix. Think about the sauropods… those giant long necked dinosaurs like Diplodocus. The RLN in them is on the order of 20 *meters* long… to cover a straight line distance of a foot!

Chapter two dives into our diets. Did you know a dog can live a long and healthy life eating rice and meat alone? They can because dogs manufacture the trace chemicals like vitamin C that they need to stay alive. But not us. A lot of our dietary foibles, like scurvy, are probably a result of growing up in a fruit rich environment. One day, the vitamin C gene broke, but since the environment already had a lot of vitamin C (e.g.:  fruit), evolution failed to notice. We are also hard wired for a feast and famine lifestyle. Except we are now in a world of constant feast, which results in runaway obesity.

Chapter three discusses some of the fun that takes place at the genetic level. As most people know, sickle cell disease is a genetic adaptation to malaria. But when a person inherits two sickle cell genes, the result is not good. 

One of the most interesting discussions was about how the immune system trains itself. In loose terms, long before you were recognizable as a human, the body set up a bunch of cells as a test bed, then breaks up various endogenous proteins and feeds them to those cells. If the cell reacts, it is killed. The upshot is all the remaining cells know how to get along with each other. Tuning of the immune system carries on for some time after birth. Allergies and auto-immune disorders are the result when this does not work. BTW: Do not buy "immune system boosters". Your immune system is in a state of balance. If you jack it up, you get  sick; if you suppress it, you get sick. Peanut and related allergies are on the rise. The "hygiene hypothesis" suggests that this is the result of anti-bacterials and over protective parents. This seems likely to be true. So let your kids get dirty… it is good for them. 

The next chapter focuses on reproduction. Why don't the fallopian tubes and the ovaries connect up directly? They should. It would avoid a lot of problems. Human child birth is extremely dangerous for both the mother and the child. Human babies are utterly helpless at birth. Our heads are enormous compared to the small hole we have to squeeze through to get born. These issues are unique to humans. A gnu calf pops out effortlessly for the mother, and is on the run within minutes. It may be that girls mature wore quickly than boys because there are many more things that can go wrong with their bodies. Nature responded by making women mature faster so they are more likely to pop out a puppy before dying.

Cancer is fascinating. If we live long enough, we will die of cancer. We think of the big C as death incarnate. But cancer is necessary for life. Cancer is runaway growth. Growth is what keeps us alive. As we age, our ability to control growth shrinks due to mutation and such, and we get cancer. Without mutation, life would not be possible. With mutation, life is a bitch.

The final chapters went off the rail for me and I only skimmed them. It discusses at length our cognitive errors, such as confirmation bias. I am already familiar with these "errors" and I largely skipped this chapter, and the next, which focuses on the large "why are we here" kind of issues.
This book has its moments, but I thought it strayed from its topic when it came to psychology. It is a good book to draw evolution examples from. In this case, the foot print of evolution is errors and compromises, not design. If all this sounds compelling to you, I recommend the book.      

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