By David P. Barash

Among the many misconceptions about evolution -- "it's only a theory"; "it works for the good of the species" -- one is that evolution generates biological perfection. If only! In "The Evolution of Imperfection," Laurence D. Hurst, a professor of evolutionary genetics at the University of Bath, does a nearly perfect job of showing how and why, as his subtitle indicates, "we aren't and can't be perfect."

Mr. Hurst begins with an account of how natural selection creates extraordinary adaptations of the sort that biologists are proud of identifying and studying -- stick insects perfectly resemble sticks; some flowers mimic female bees, deceiving male pollinators; bats use sonar to detect flying moths who in turn have evolved acute sensing mechanisms that help them avoid predators. "Given the commonness of apparent perfection in nature," Mr. Hurst observes, "it might seem somewhat perverse to be writing a book about the evolution of imperfection. Isn't it like having the best meal ever cooked for you and complaining that the napkins weren't folded to your liking?"

His goal isn't to complain, but to open our eyes to how evolution really works and to explain the perplexing development of traits that do not enhance evolutionary fitness. Humans can't synthesize their own vitamin C, for instance -- our ancestors lost the ability because they had access to plenty of fruit. But this was bad news for the 18th-century British sailors who developed scurvy on a diet of hardtack and salt pork. Higher blood pressure during pregnancy helps get extra nutrients to the fetus, but the skyrocketing blood pressure of preeclampsia results from an evolutionary tug of war in which the fetus tries to get more nutrients than is healthy for the mother.

Such a catalog of biological imperfections undercuts claims that we, or any other creatures, result from intelligent design. Instead, evolution is a result of natural selection, a mindless iterative process that works with whatever material is at hand. It cannot plan ahead and is therefore susceptible to many suboptimal outcomes, so long as they are better than available alternatives.

Following an unusually palatable review of modern genomics -- the study of the whole of an organism's DNA -- Mr. Hurst offers insight into how mutations happen and why they often persist, especially if they're recessive. He describes the immense amount of noncoding DNA, only recently recognized, that holds on to a huge reservoir of potentially troublesome genetic errors. Attentive readers will learn about introns, exons, pseudogenes and defective jumping genes, all prime candidates for generating genetic blunders.

"The Evolution of Imperfection" usefully summarizes the sources of most suboptimal outcomes. For one thing, evolution takes time, hence the phenomenon of "evolutionary lag": Many generations are required for it to have significant effect, and humans have relatively long lives. At the same time, some short-generation organisms change rapidly, so slow-breeding Homo sapiens is frequently unable to adapt to fast-moving pathogens such as Covid-19, malaria and flu.

One reason we are sometimes ill-suited to our world is that cultural evolution has far outstripped its biological counterpart. Our ancestors evolved to take advantage of fats and sugars whenever possible, but now we tempt ourselves with harmful excesses of both. Similarly, the "hygiene hypothesis" suggests that modern cleanliness has reduced exposure to nonlethal antigens, rendering us more vulnerable to asthma and autoimmune diseases.

Evolution is a tinkerer, not a creator. It deals with existing structures, rarely producing new ones from scratch. And so our knees and lower backs -- adapted for the horizontal posture of a quadruped -- are frequent pains in our, well, knees and lower backs. Similarly, men are stuck with a poorly engineered prostate and women with a birth canal that is sometimes too narrow for a newborn's big-brained head.

"Perhaps the strangest of all parts of our biology," as Mr. Hurst puts it, "is how bad we are at making babies. Surely after millions of years we would at least have gotten this right!" But no. Human embryos are especially prone to anomalies in chromosome number, though most of those result in death before pregnancy is even detected. Such imperfections arise largely because, for most of our evolutionary history, we had relatively small population sizes, which deprived our ancestors of potent selection opportunities for more efficient baby-making.

Mr. Hurst focuses mostly on our many genomic liabilities. He is especially adroit with metaphors: He conjures dartboards, staircases and roulette wheels while providing a solid introduction to such concepts as the evolution of the sex ratio (why it's nearly always 50/50), frequency-dependent selection (in which a trait is positively selected when rare, but disadvantaged when abundant) and neutral mutations, which troublesomely clutter the genome. Readers will also encounter a complex and valuable explanation of why human DNA is especially, perhaps uniquely, susceptible to accumulating lots of mutations. Also -- crucially important -- Mr. Hurst presents a thoughtful expert's account of the perils and prospects of gene therapy.

Add up our genetic liabilities -- we are, as Mr. Hurst laments, such aggressive "hoarders of DNA junk" that as a result, "rare diseases collectively aren't rare" -- and it's remarkable that we're such a successful species. Yet he is contagiously enthusiastic about the simple yet stunning reality of our very existence: "It is worth understanding that while we are not the pinnacle of evolution, nonetheless the marvel of life remains glorious, despite our imperfections."

--Mr. Barash is an evolutionary biologist and professor emeritus of psychology at the University of Washington. His next book, to appear this fall, will be "The Soul Delusion."

(END) Dow Jones Newswires

June 29, 2025 11:19 ET (15:19 GMT)

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