If there is one thing that infuriates me about the way the human body works, it is the fact that our throat is a passage for both food and air. I am sure that anyone who has gone down in a fit of coughing can attest to this. As Nathan Lents shows in his amusing book Human Errors, that is just the tip of the faulty iceberg.

Anatomical quirks such as the above are probably the ones we are all most familiar with. As mentioned in my recent review of Eyes to See: The Astonishing Variety of Vision in Nature, eyes have independently evolved multiple times and nature offers different solutions for capturing light. Why, then, do the photoreceptors in our eyes face backwards, with the big bundle of nerves exiting the eyeball creating a blind spot? Cephalopods seem to have their eyes wired in a more logical way. You might also have heard of the recurrent laryngeal nerve that innervates our larynx. Rather than running from the brain straight to our voicebox, this nerve takes a circuitous route, looping around our aorta. In long-necked species such as giraffes this means metres of unnecessary nerve!

The answer, as any evolutionary biologist will tell you, is that these faults reveal much about how we evolved from our distant ancestors. Neil Shubin also discussed this in his marvellous book Your Inner Fish: The Amazing Discovery of Our 375-Million-Year-Old Ancestor. That nerve I mentioned? When we were still fish it innervated the gills, the evolutionary precursor of our larynx. With no neck to speak of, the brain, heart, and gills in a fish lie on a more or less straight line and there was no problem with the route this nerve ended up taking. However, once fish evolved into creatures with necks, it started to look a bit dumb. But alas, evolution cannot throw everything out and start from scratch, it has to work with whatever (faulty) material is at hand.

“[…] once fish evolved into creatures with necks, [the laryngeal nerve] started to look a bit dumb.”

And these kinds of bugs and quirks abound. Next to anatomy, Lents covers our dietary needs and our inability to synthesize vitamins that many other organisms make themselves. Our DNA is a veritable junkyard of broken genes, ancient viral DNA (see also Discovering Retroviruses: Beacons in the Biosphere), and stretches of self-copying DNA (or transposable elements). Together, these make up an estimated 97% of our genome and were initially designated “junk DNA”, though there has been a bit of a push-back against the idea that this material is completely useless (see e.g. Junk DNA: A Journey Through the Dark Matter of the Genome or The Deeper Genome: Why There is More to the Human Genome Than Meets the Eye).

And then there is our reproduction, marred by poor fertility and high mortality during childbirth. Autoimmune diseases, allergies, optical illusions, false memories, cognitive biases… True to the promise of the book’s subtitle, Lents offers a panorama of our glitches, and there is something here for everyone to enjoy.

I found the chapter on our brain and its quick-and-dirty heuristics (i.e. problem-solving routines) particularly fascinating. Our cognitive biases and weaknesses regularly drive us to make poor choices, and this knowledge is ruthlessly exploited by advertisers, casinos, or astrologers, to name a few. I also find them particularly interesting as they lead to much irrational behaviour and persistent belief in pseudoscience (for more on that, see amongst others Thinking, Fast and Slow or Suspicious Minds: Why We Believe Conspiracy Theories).

“Our cognitive biases and weaknesses [are] ruthlessly exploited by advertisers, casinos, and astrologers.”

Do not let its focus on our many flaws fool you. Human Errors is an excellent piece of popular science, that, far from being a downer, is more a laugh-out-loud romp that will give you reason to marvel at our ability to be successful despite all our imperfections. Some of these are truly pointless, others result from trade-offs, others still have been turned from bugs into features, and not infrequently things that used to serve us well in our evolutionary past no longer do so now (see e.g. The Hungry Brain: Outsmarting the Instincts That Make Us Overeat, Mismatch: The Lifestyle Diseases Timebomb, or Mismatch: How Our Stone Age Brain Deceives Us Every Day And What We Can Do About It). But with all of them, Lents explains plainly and clearly how evolution works and is shaped by what has come before.

As a final aside, you will notice that I have carefully steered clear of using the word “design” in this review, tainted as it has become by creationist appropriation. But if I must: yes, humans seem poorly designed on many fronts compared to other organisms. If you were an engineer tasked with designing a human, you would make many changes. In this context, Adam Rutherford said that this book shows that: “if there is an intelligent designer, he is comically hopeless”. Quite.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

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