We humans like to think of ourselves as highly evolved creatures. But if we are supposedly evolution’s greatest creation, why do we have such bad knees? Why do we catch head colds so often—two hundred times more often than a dog does? How come our wrists have so many useless bones? Why is the vast majority of our genetic code pointless? And are we really supposed to swallow and breathe through the same narrow tube? Surely there’s been some kind of mistake.
As professor of biology Nathan H. Lents explains in Human Errors, our evolutionary history is nothing if not a litany of mistakes, each more entertaining and enlightening than the last. The human body is one big pile of compromises. But that is also a testament to our greatness: as Lents shows, humans have so many design flaws precisely because we are very, very good at getting around them.
A rollicking, deeply informative tour of humans’ four billion year long evolutionary saga, Human Errors both celebrates our imperfections and offers an unconventional accounting of the cost of our success.
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About the Author
NATHAN H. LENTS is a professor of biology at John Jay College, CUNY and the author of Not So Different: Finding Human Nature in Animals. He has appeared as a scientific expert in a range of national media, including The Today Show, NPR, Access Hollywood, 48 Hours, and Al Jazeera America. He lives in Queens, NY.
Read an Excerpt
We love to admire physical excellence. We can’t get enough of massive bodybuilders, graceful ballerinas, Olympic sprinters, shapely swimsuit models, and hardy decathletes. In addition to its innate beauty, the human body is also dynamic and resilient. The carefully orchestrated functions of the heart, lungs, glands, and GI tract are truly impressive, and we continue to discover the elaborate intricacies through which the body maintains its health despite the onslaught of a changing environment. Any discussion of the shortcomings of our physical form must first begin with an acknowledgment that the beauty and capability of the human body far outshines the few odd quirks here and there.
But quirks there definitely are. Lurking in our anatomy are some odd arrangements, inefficient designs, and even outright defects. Mostly, these are fairly neutral; they don’t hinder our ability to live and thrive. If they did, evolution would have handled them by now. But some are not neutral, and each has an interesting tale to tell.
Over millions of generations, human bodies morphed tremendously. Most of our species’ various anatomical structures were transformed in that metamorphosis, but a few were left behind and exist now purely as anachronisms, the whispers of days long gone. For instance, the human arm and the bird wing perform totally different functions but have striking structural similarities in the scaffolding of their bones. That’s no coincidence. All quadruped vertebrates have the same basic skeletal chassis, modified as much as possible for each animal’s unique lifestyle and habitat.
Through the random acts of mutation and the pruning of natural selection, the human body has taken shape, but it’s not a perfect process. A close inspection of our mostly beautiful and impressive bodies reveals mistakes that got caught in one of evolution’s blind spots — sometimes literally.
I Can’t See Clearly Now
The human eye is a good example of how evolution can produce a clunky design that nonetheless results in a well-performing anatomical product. The human eye is indeed a marvel, but if it had been designed from scratch, it’s hard to imagine it would look anything like it does now. Inside the human eye is the long legacy of how light-sensing slowly and incrementally developed in the animal lineage.
Before we consider the puzzling physical design of the eye, let me make one thing clear: The human eye is fraught with functional problems as well. For instance, many of the people who are reading this book right now are doing so only with the aid of modern technology. In the United States and Europe, 30 to 40 percent of the population have myopia (nearsightedness) and require assistance from glasses or contact lenses. Without them, their eyes do not focus light properly, and they cannot make out objects that are more than a few feet away. The rate of myopia increases to more than 70 percent of the population in Asian countries. Nearsightedness is not caused by injury. It’s a design defect; the eyeball is simply too long. Images focus sharply before they reach the back of the eye and then fall out of focus again by the time they finally land on the retina.
Humans can also be farsighted. There are two separate conditions that cause this, each resulting from a different design flaw. In one, hyperopia, the eyeballs are too short, and the light fails to focus before hitting the retina. This is the anatomical opposite of myopia. The second condition, presbyopia, is age-related farsightedness caused by the progressive loss of flexibility of the lens of the eye, the failure of the muscles to pull on the lens and focus light properly, or both. Presbyopia, which literally translates as “old-man sight,” begins to set in around age forty. By the age of sixty, virtually everyone has difficulty making out close objects. I’m thirty-nine, and I have noticed that I hold books and newspapers farther and farther from my face each year. The time for bifocals is nigh.
Add to these common eye issues others such as glaucoma, cataracts, and retinal detachment (just to name a few), and a pattern begins to emerge. Our species is supposed to be the most highly evolved on the planet, but our eyes are rather lacking. The vast majority of people will suffer significant loss of visual function in their lifetimes, and for many of them, it starts even before puberty.
I got glasses after my first eye exam, when I was in the second grade. Who knows how long I had actually needed them? My vision isn’t just a little blurry. It’s terrible — somewhere around 20/400. Had I been born before, say, the 1600s, I would probably have gone through life unable to do anything that required me to see farther than arm’s length. In prehistory, I would have been worthless as a hunter — or a gatherer, for that matter. It’s unclear if and how poor vision affected the reproductive success of our forebears, but the rampant nature of poor vision in modern humans argues that excellent vision was not strictly required to succeed at least in the most recent past. There must have been ways that early humans with poor vision could have thrived.
Human vision is even more pitiable when compared with the excellent vision of most birds, especially birds of prey such as eagles and condors. Their visual acuity at great distances puts even the sharpest human eyes to shame. Many birds can also see a broader range of wavelengths than we can, including ultraviolet light. In fact, migrating birds detect the North and South Poles with their eyes. Some birds literally see the Earth’s magnetic field. Many birds also have an additional translucent eyelid that allows them to look directly into the sun at length without damaging their retinas. Any human attempting to do the same would most likely suffer permanent blindness.
And that’s just human vision during the day. Human night vision is, at best, only so-so, and for some of us it is very poor. Compare ours with cats’, whose night vision is legendary. So sensitive are cats’ eyes that they can detect a single photon of light in a completely dark environment. (For reference, in a small, brightly lit room, there are about one hundred billion photons bouncing around at any given moment.) While some photoreceptors in human retinal cells are apparently able to respond to single photons, these receptors cannot overcome background signaling in the eye, which leaves humans functionally incapable of sensing just one photon and thus unable to perform the sorts of visual feats that cats pull off so easily. For a human to achieve conscious perception of the faintest possible flash of light, she needs five or ten photons delivered in rapid succession, so cats’ vision is substantially better than humans’ in dim conditions. Furthermore, human visual acuity and image resolution in dim light is far worse than that of cats, dogs, birds, and many other animals. You might be able to see more colors than dogs can, but they can see at night more clearly than you.
Speaking of color vision, not all humans have that either. Somewhere around 6 percent of males have some form of colorblindness. (It’s not nearly as common in females because the screwed-up genes that lead to colorblindness are almost always recessive and on the X chromosome. Because females have two X chromosomes, they have a backup if they inherit one bum copy.) Around seven billion people live on this planet, so that means that at least a quarter of a billion humans cannot appreciate the same palette of colors that the rest of the species can. That’s almost the population of the United States.
These are just the functional problems with the human eye. Its physical design is riddled with all sorts of defects as well. Some of these contribute to the eye’s functional problems, while others are benign, if befuddling.
Table of Contents
Introduction: Behold the Blunders of Nature ix
1 Pointless Bones and Other Anatomical Errors 1
2 Our Needy Diet 35
3 Junk in the Genome 65
4 Homo sterilis 93
5 Why God invented Doctors 127
6 A Species of Suckers 157
Epilogue: The Future of Humanity 197
Most Helpful Customer Reviews
I came across this on NetGalley but as it had already been published I decided to purchase a copy for myself as I haven't bought a medical text for a few months. I am always drawn to books with a medical element to them and this sounded as though it would be incredibly interesting with the added benefit of learning more about myself. This intriguing non-fiction book details the design flaws us humans have and their advantages and disadvantages too. Sometimes purely fact driven writing can come across as both tedious and heavy but I didn't feel this at all here. I have mentioned before that I read quite a few books that I can learn something from and this fits perfectly into that category. Nathan H. Lents has ensured that the writing is straightforward and easy to follow so that it can be read and understood by those who are not part of the medical profession, and has excelled in penning a thoroughly engaging narrative for readers to appreciate. Highly recommended to everyone! I mean, who doesn't want to learn more about their own body and its evolution?
[NOTE: I received a copy of this book through NetGalley.] I found this to be both an informative and entertaining read. While the author doesn’t delve very deep into details (each subject in each chapter would probably warrant a book of its own), and although I wish there had been more developed explanations at times, I’m also aware that one book couldn’t tackle everything in one go—and he nevertheless provides enough information for a reader to go on research some more later on a given topic. I already knew some of the ‘human errors’ presented in the book (such as junk DNA and mutations), but definitely not others, such as why we get so many headcolds (our sinuses placed the wrong way), why we do actually make our own B12 vitamin but can’t use it (same with other vitamins—and this is why we need a varied diet, with all the problems it entails), or why our ways of procreating are, in fact, very inefficient compared to those of other mammals. So, discovering all this was fascinating, and the explanations provided also satisfy the unavoidable ‘why’ questions that rose immediately after (I’m very much a why person; every physician who attended me since I’ve learnt to speak can testify to this). For instance, we lost the ability to make our own vitamin C, whose absence will lead to scorbut and kill us; but the mutation that led to this defect wasn’t erased through evolution because it happened in areas where fruit was easily available, and a diet of fruit would compensate for our rotten GULO gene… until the latter stuck, happily passed around to descendants. I liked that some explanations went a bit further: it’s not only about this or that physical defect, but also about how we’re still wired for survival techniques and reactions dating back to prehistoric times, and how some of our modern behaviours are thus impacted. An extended example would be gambling, and why people in general have irrational reactions such as ‘now that I’ve lost ten times in a row, I -must- win, there’s no other way’ (though statistically, you could lose an 11th time), or will bet more and more when they’re on winning streak, and risk losing it all or more, rather than save those earnings. Those would go back to the way we interpreted situations to learn from them and survive (man sees a lion in a bush, concludes bushes often hide a lion, and then avoids bushes). Same with optical illusions, due to our brains’ ability to ‘fill in the blanks’. On the side of actual errors, I noticed a few (redundant words or phrases, that a last editing pass would probably remove). Nothing too bad, though. Conclusion: Due to the lack of deeper details and general simple writing, this book is probably more for laypeople rather than people with a strong scientific background—but even then, there’s still a chance that some of the ‘human errors’ may still be of interest to them.