Human Errors by Nathan Lents

Photoreceptors in our eyes face backwards instead of, you know, facing forward where all the light is. Octopi and other cephalopods don’t have this problem. Nobody know why this happened.

See the image below from Wikipedia:

Our maxillary sinuses (sinuses are empty spaces located within the bones of our skull and face) have drain holes on the top instead of, you know, the bottom where all the mucus could drain our because of a thing called gravity.

What kind of plumber would design sink with the drain pipe located at the top?

This happened because “As our primate ancestors evolved, however, there was less reliance on smell and more reliance on vision, touch, and cognitive abilities. Accordingly, the snout regressed, and the nasal cavities got smushed into a more compact face.“. See the image below.

The recurrent laryingeal nerve takes an unnecessary detour. It has to go from the brain to the larynx but instead of taking the direct route it first loops around the aorta before returning to the larynx. Its cousin, the superior laryngeal nerve, does not engage in any of this nonsense (see the image below from Wikipedia).

This happened because once upon a time when we used to be fish, the larynx was actually the gills and the nerves connecting to the gills weaved around the tubes of the heart for space saving (since there’s not much of it to spare in a fish’s body), but as we evolved into vertebrates the design persisted and here we are.

The Brain is protected by the skull, the heart and lungs by the rib cage, but the connection between them, the neck, is left unprotected: The neck, whose integrity is vital to our survival, is one is most vulnerable parts since it is devoid of any bony protection, and the trachea is literally “protected” by only a thin layer that can be easily punctured.

Also, why do we have the same tube for breathing and swallowing? What can possibly go wrong? “It also doesn’t help that the human instinctual physical reaction when startled is to gasp.“. Very good, make sure that piece of food really gets stuck down the wrong tube.

“The anatomical adaptation to upright walking never quite finished in humans.“.

The mesenteries attach to the back of the abdominal cavity instead of the top. Mesenteries are thin sheets of tissue that keep your intestines held together in place.

The Achilles tendon is not only unprotected, it also lacks redundancy and takes most of the strain of the ankle joint. But at least it can be strengthened through exercise, unlike the ..

… ACL, that you cannot strengthen through exercise and (as an added bonus) is put under much more strain than it was designed for. A gift from the good old days when we evolved from being on all fours to standing and the muscles that used to share the load got free while the bones and tendons took on the added responsibility.

Also, “In all vertebrates except us, the spinal disks are positioned in line with the normal posture of that animal … In humans, the vertebral disks are in an arrangement that is optimal for knuckle-draggers, not upright walkers.“

Our wrists have too many bones, so do our feet.

“The seven bones of the human ankle (shown in white) are fixed in place relative to each other. No engineer would design a joint with so many separate parts, only to fix them together — yet incredibly, most humans manage just fine with this jumbled arrangement.“

We also a have a tailbone but no tail.

Essential vitamins and minerals are called “essential” not because they’re required any more than the “non-essential” ones but because our bodies cannot make them on its own, we must consume them in our food. A problem that many other animals do not have.

Take vitamin C for example, other animals can synthesise it inside their bodies just fine, but humans (along with fruit bats for some reason) cannot. What do we get instead? Scurvy. The gene that contains the instructions to make vitamin C, GULO, is unreadable in humans, more specifically, became unreadable due to a random mutation.

In fact, deficiency of any of the essential stuff leads to a host of diseases like beriberi (vitamin B1 deficiency), goitre (iodine deficiency), rickets (vitamin D deficiency) – So one would think that evolution would’ve made sure that the genes that code for the stuff needed to make these would remain intact, but alas that is not how evolution works, and here we are.

There are essential amino acids as well, again, called essential because our bodies have lost the ability to manufacture them, there are nine of them.

Then there are essential fatty acids, there are two of them.

The reason that we didn’t die off when we lost the ability to make this essential stuff is likely that our ancestors manage to put together a diet that provided them with the stuff, so the lack was never felt. Their lineage only found out about it much later when for some reason they could not eat the essential nutrients.

Yes, our bodies no longer had to expend the few calories necessary to synthesise the essential nutrients, but it seems a poor trade-off given this capricious world can rid us of our food supplies pretty quickly (famine, forest fires etc.). Seems pretty short sighted.

And then there is the fact that some nutrients actually prevent other nutrients from being absorbed in the body. For examples, foods like legumes and nuts hinder our ability to absorb iron (same for calcium rich foods like milk) and foods containing oxalates (like spinach) hinder our ability to absorb calcium (so much for my preference for “palak paneer”) – Hence Lents’ sage advice “It’s not enough to eat the right foods to meet our exacting dietary needs; we must eat those foods in the correct combinations.“.

Well, maybe “junk” is an oversimplification and it is likely that we don’t know enough about DNA and mislabel parts of it as being worthless. So, let’s not call it “junk”, okay? Instead, let’s look at that we do know: Only 3% of our DNA is genes that actually do something. Genes lead to proteins and proteins do stuff in our bodies that results in us being alive. “… most of the remaining 97 percent is gobbledygook.“. Useful or not, our bodies dutifully duplicate everything in the 46 chromosomes every time a cell divides. How many times? Roughly about a million times a second. Why spend all that energy duplicating data that is not very useful? “You expend a few dietary calories every single day just to copy your largely useless DNA.“.

By the way, in all that duplication there is a chance for DNA replication errors. Even though DNA replication is a very high fidelity affair, due to the sheer number of things that need to be copied, mistakes are bound to happen (we call these “mutations“). Now, since most of the stuff in our DNA is not very useful most of these mutations do not impact us. But if we happen to get a mutation in a part of DNA that is actually useful then it is bad news as it can disrupt the functioning of the gene and lead to genetic diseases like Sickle Cell Disease or Huntington’s Disease and even cancer. And if the mutation happens in the sperm or egg cell then it will also be carried down generations.

There are pseudogenes, which are like broken copies of genes. They look a lot like normal genes, but due to mutations that happened in our evolutionary past, they no longer function properly. Think of them as old, non-working versions of genes that got “turned off” over time – like the GULO gene I mentioned previously. These pseudogenes can still be found in our DNA, but they don’t produce any proteins or have any active roles in our bodies. We have close to twenty thousand pseudogenes in our DNA, almost as much as we have useful ones.

Then there is the viral DNA inside our DNA courtesy retroviruses. Retroviruses are viruses that insert a copy of their RNA genome into the DNA of a host cell, using an enzyme called reverse transcriptase, which converts their RNA into DNA. Once integrated, the viral DNA becomes part of the host’s genetic material, allowing the virus to replicate along with the host cell’s DNA.

For the virus this is great news, since it need not do any more work for propagation. It’s not so much good news for the host human, but thankfully the viral DNA in our DNA is so heavily mutated after all these years that it does not harm us. Around 8% of our DNA is viral DNA, more than we have useful DNA.

Finally, there are transposable elements (TEs). They are also known as “jumping genes” – sequences of DNA that can move or “transpose” themselves to different positions within the genome. “Nearly half of human DNA is made of autonomously replicating, highly repetitive, dangerously jumping, pure genetic nonsense that the body dutifully copies and maintains in each one of its billions of cells.“.

Um, I’m not so sure about this, because while this repetitive behaviour can sometimes disrupt genes and cause mutations, it also plays a role in genetic diversity and evolution. Over long periods, these elements can contribute to the development of new genes and regulatory sequences, adding to the complexity of an organism’s genome.

“We are some of the most inefficient reproducers in the animal world because we have errors and flaws throughout almost the entire reproductive process, from the production of sperm and eggs to the survival of our children.“.

Human female attain puberty later than other primates. Not a good strategy for evolution because the females can die before being able to bear kids.

Ovulation is concealed in humans, so neither the girl nor the guy knows when the time is right (modern health tech. like smart watches may be helping solve this though). Human babies are born too early (altricial stage) because the human female birth canal is too narrow for the baby’s large head to pass through.

This is one of the reason that human birth is more dangerous than births of other primates. Plus a bunch of other issues like failure to implant, chromosomal abnormalities, insufficient HCG secretion and ectopic pregnancy.

Autoimmune diseases like myasthenia gravis, Graves’ disease and lupus. Allergies like ones from peanuts, milk and eggs. Congenital defects and abnormalities: Lents talks about septal defect, transposition of the great vessels and anastomosis but there are many others like spina bifida, congenital hip dysplasia, gastroschisis, the list is long.

And of course, cancer, the “… ultimate bug-and-feature of nature …” per Lents. Cancer is when a cell forgets its place as part of a grand system and starts to selfishly focus on its own growth at the expense of the whole – a little like humans on planet earth.

Lents calls it both a bug and a feature because it is the result of genetic mutation going awry but it is the same principles of mutation that got us here in the first place – a little like human greed was the reason that we developed ingenious ways of getting what we want, but it is the same greed that led to a lot of avoidable waste, harm and suffering.

We fall prey to optical illusions and see motion where there is none, a different image depending on how we look at it, more colours than there are, lines of differing lengths when they’re actually the same, see faces way too often when there are none and of course there is The Dress.

Cognitive biases – I have written about several cognitive biases previously. One of my favourites ones are argument from ignorance and anchoring. Cognitive biases are behind so much sub-optimal decision making in the world. Here is a fantastic image from Wikipedia on the many biases we have.

Faulty memory: It is easy to implant false memory in humans. Even easier if we want to believe what is being implanted. Our minds are not really concerned about the absolute truth as much as it is concerned about a story that makes enough sense that they can live with.

Over reliance on heuristics: Mental shortcuts that we take and end up in the wrong place. Representativeness heuristic, recognition heuristic, affect heuristic are ones I am fascinated by.

The refrain in many parts of the book is some version of: there is “no easy way for evolution to reprogram” [insert limitation/example of poor design/defect here]. This makes sense because evolution is the process of the “good enough” and not the “most optimal”. As long as an organism’s physical design or mental algorithms are good enough for it to propagate its genes to the next generation evolution will see no reason to make changes.

It is also interesting to consider that we’ve somehow slowed down or modified the evolutionary process because of our scientific and technological progress. Lents says “… science has effectively short-circuited evolution …”. Yes, there is truth to this. Modern medicine is able to thankfully give a life to thousands who would have perished a few centuries ago, not to mention the life expectancy which is trending towards 80 years for many countries.

But in doing so, the beings that natural selection would previously have weeded out (pardon the callousness) get to live. The sub-optimal parts of our design that would have faced evolutionary pressure to improve do not any more. Yes, evolution is still taking place, indeed there should be more genetic diversity in humans today), but a favourable mutation is not the decisive advantage it used to be.

Another point is that many of the “limitations” I mentioned till now were (and are) features, that in our rapidly changing modern world, have become bugs. Think of the cognitive biases and mental heuristics that trip us up today, these were made for a very different world. For example, relying on readily available memories helped early humans assess risks quickly (availability heuristic), however, in the modern world, media coverage can skew perceptions of risk, making rare events (like plane crashes) seem more common than they are.

And physical features like wisdom teeth that helped our ancestors to chew a tough, fibrous diet are not needed as much today and are often the cause of pain and discomfort. Or our back: the human spine evolved to support a quadrupedal stance, and adapting it for upright bipedalism has led to a range of issues, including lower back pain and herniated discs. The structure of our spine is not ideally suited for the stresses of modern sedentary lifestyles.

And the great feature/bug – our mind, which as I said before has given us all the great advantages we enjoy today but also the unnecessary suffering we endured to get here – our minds are evolutionary double-edged swords, “… evolution rewarded those of our ancestors who could nimbly switch between cooperation and competition when the conditions suited them.“.