It can be said that evolution works on the principle of “good enough.” Consider the bat. While other airborne creatures can glide gracefully across the sky, bats seem to stay aloft by sheer willpower, thrashing as if they’re about to have a heart attack in mid-air. But as long as they can fly well enough to feed and reproduce, evolution figures, eh … good enough.
Human Errors: A Panorama of Our Glitches, from Pointless Bones to Broken Genes is a collection of “good enough” body parts and functions accumulated over time, describing our current grab bag of features, some of which actually cause us harm or prevent us from having children that can walk immediately after birth. It’s kind of like having a very hard look at ourselves in the mirror.
Although it’s not a comprehensive list, author Nathan H. Lents walks us through a number of the bodily flaws that have been retained throughout human evolution. It reads a bit like a listicle of “stuff-you-didn’t-know-your-body-sucks-at”, but it’s an interesting and informative listicle.
Lents devotes separate chapters to pointless organs, unnecessarily diverse dietary needs, useless genes, fertility issues, and diseases. There’s also a chapter on psychological failings, such as our extremely unreliable memory which, depending on where you stand on mind-body duality, can still be construed as a biological failure. Each of these chapters could be expanded to full tomes of their own, but Lents does a decent job of skimming the surface and putting together a fun, easy-to-read rundown of curios for us to mull over.
While it’s interesting to catalogue our many exaptations — features that perform functions beyond their original use — Lents falls short of putting them into a larger evolutionary context, particularly in the chapters dealing with anatomy. It feels like a missed opportunity to provide the reader with a deeper understanding of our evolutionary and developmental past.
Many of our unnecessary body parts or overly complicated wiring likely exist because of an evolutionary bottleneck in fetal development termed the “developmental hourglass hypothesis,” which posits the conservation of the vertebrate body plan is partially due to the developmental constraints of the mid stages of embryonic development . This model has received some molecular support in recent studies, so it seems to be gaining speed.
In human speak, that means all vertebrates, chicken to whale, have to go through a very similar developmental stage, which closely resembles an ancestral one. Lots of further elaborations allow for diversification of forms, but each has to work around those constraints. That’s why the larynx nerve loops around the aorta for no reason, as described in chapter 1. It got stuck there during an early conserved stage and now we have to deal with a workaround.
Another missed opportunity in chapter 1 is the lack of developmental explanations for some of our more interesting body parts. Lents notes humans have added vertebrae in their spinal column, which helps maintain our posture and direct our center of mass over the pelvis. “Apparently, evolution can duplicate bones when needed,”Lents says.
Yes it can, but there is a more interesting explanation as to why it can do that. Humans are like earthworms, in that we’re segmented. Think about our repeating pairs of vertebrae and ribs. It’s “easy” for evolution to add segments by simply turning on a few genes (or even just one). That’s why some people have extra sets of ribs, called either lumbar or cervical ribs, depending on whether they are originating from the back or the neck.
Most of these conditions are asymptomatic, suggesting they can persist in the population without any ill effects. Including these developmental explanations would have put the idea of duplicating or deleting segments into an evolutionary context.
On the other hand, Lents does a good job of explaining the nuances of our strange dietary needs. While we know that humans have lost the ability to synthesize some vitamins, shifting to external supplies derived from food sources, he outlines a complex relationship between the agricultural revolution and the rise of more refined foods, leading to a shortage of B1 vitamin and resulting in a disease induced by civilization itself, beriberi.
Lents falls short, however, of calling out the supplement industry, and in some cases makes claims in need of more support. “Without constant calcium and vitamin D supplementation,” Lents says, “most people would develop the brittle bones of osteoporosis in their golden years.” What’s not discussed is the rates at which these vitamins are absorbed, how bioavailable they are in their most commonly marketed form, and the best way to take them, if the need arises.
The most puzzling part of Human Errors is the epilogue, a meandering bit of writing that casts a very gloomy shadow over an otherwise up-beat book. Here Lents tries to answer questions only tangentially related to our poor design, such as the possibility of extraterrestrial life and if humanity will inevitably destroy itself. It’s not clear how this relates to our basic biology, hinting at our self-destruction as a function of our lack of … empathy? Foresight? Self-control?
On top of that, there are some obvious truisms thrown in, again without reference. Lents states that rain forests are the primary carbon dioxide sinks, but according to a few sources, it’s actually the oceans. This is a systemic issue of the book, general statements that sound true muddled in with the real stuff.
Overall, the text is relatively free of jargon and accessible, no easy feat for scientists used to dry academic writing, Lents’ somewhat stilted jokes notwithstanding. The sparse citations are at least from primary sources, but aren’t noted in the main text, which makes it difficult to identify a source while reading.
Human Errors: A Panorama of Our Glitches, from Pointless Bones to Broken Genes is guaranteed to ruffle some feathers. There are lots of people that continue to hold up the human form as either a pinnacle of evolution or the divine and perfect creation of God. Though the delivery isn’t always pristine, Lents effectively shows it’s just an assembly of available and reworked parts that get the job done, at least for a while.