If God created man in His own image, He must have had remarkably poor eyesight. In the United States and Europe, roughly 40 percent of the population is nearsighted, requiring glasses or contact lenses to see clearly at a distance. In many Asian countries, the figure is nearly twice as high. Human vision, compared to other animals, is hardly something to brag about.

The human eye, long celebrated as a marvel of biological engineering, is riddled with design flaws. Chief among them is the inverted retina, in which the light-sensitive cells face backwards, forcing incoming light to pass through several layers of neural tissue before reaching them. This arrangement also requires the optic nerve to punch through the retina, creating a blind spot and leaving the retina vulnerable to detachment. It would be a bit like an engineer designing a new television with the power cord running through the middle of the screen.

If the human eye is the product of intelligent design, what are we to make of the fact that other animals, presumably fashioned by the same designer, manage to avoid many of its pitfalls? Cephalopods, for instance—including octopuses and squid—have non-inverted retinas, eliminating the structural problem that leaves humans with a blind spot. Additionally, eagles enjoy visual acuity more than twice that of humans, cats see far better in low light, and mantis shrimp possess up to 16 types of photoreceptors, compared with just three types of cones in the human eye. Meanwhile, approximately 6 percent of human males are colorblind, unable to distinguish even the relatively limited spectrum of colors available to the rest of us.

The list of eye disorders is long: cataracts, glaucoma, macular degeneration, retinal detachment, and even the annoying floaters that drift across our field of vision, just to name a few. But the faulty wiring remains the most telling defect—and makes one wonder why God managed to install the retina correctly in an octopus but couldn’t get it right in his supposed crowning achievement.

Perhaps God is not the best explanation for our jerry-rigged eyes.

Biologists now believe the inverted retina is largely a consequence of our evolutionary ancestry. Vertebrate eyes evolved from light-sensitive structures in which photoreceptors developed facing away from incoming light and toward the underlying retinal epithelium. Rather than redesigning this arrangement, evolution worked with what it had by modifying the existing structure over hundreds of millions of years. The result is a functional but imperfect arrangement in which light must pass through layers of neural tissue before reaching the photoreceptors, and the optic nerve must penetrate the retina, creating a blind spot. Octopuses, which evolved camera-type eyes independently, developed a non-inverted retina and avoided this particular compromise.

Evolution, in other words, explains what intelligent design cannot: why human vision is burdened with so many glaring design flaws, even when other species have evolved far better solutions to the same problems.

But our anatomical flaws reach far beyond the human eye. We could catalogue dozens, if not hundreds, of other anatomical quirks and biological shortcomings, from head to toe, that point either to an astonishingly incompetent designer or to the unmistakable fingerprints of our evolutionary past. The more we learn about biology, the more difficult the evidence becomes to reconcile with intelligent design. Either an unguided evolutionary process imperfectly sculpted the human body, or its supposed designer is guilty of some spectacularly poor engineering. Omniscience, it seems, is off the table.

Consider just a few examples: Why would an intelligent designer give us a tailbone without a tail, a laryngeal nerve that takes an absurd detour around the aorta before doubling back toward the neck, an appendix that can become dangerously inflamed and rupture, a shared passageway for air and food that leaves us vulnerable to choking, wisdom teeth that often have nowhere to grow, a spine poorly adapted to the demands of upright walking, and a disabled gene that prevents us from synthesizing our own vitamin C—leaving us susceptible to the debilitating disease of scurvy?

Humans, in fact, have more dietary requirements than almost any other animal in the world. In addition to our inability to synthesize vitamin C, we must obtain several essential amino acids and fatty acids from our diet, and depend on a steady supply of vitamins and minerals to keep our bodies functioning. Even our canine companions are spared some of these defects. As the biologist Nathan H. Lents observed:

So how can dogs live on meat and rice, neither of which has any vitamin C whatsoever, and not develop scurvy? They make their own. In fact, nearly all animals on the planet make plenty of their own vitamin C, usually in their livers, and thus have no need for it in their diets. Humans and other primates are nearly alone in the need for dietary vitamin C (although guinea pigs and fruit bats have this problem as well). This is because, somewhere in our evolutionary past, human livers actually lost the ability to make this micronutrient.

In this one example alone, God could have spared millions of people from centuries of needless suffering and death simply by giving us a functional gene for vitamin C synthesis—one that works perfectly well in our pets but is defective in most primates, including ourselves.

So which explanation is more plausible: that our omnipotent creator somehow managed to equip a chihuahua with a functional vitamin C gene but left humans with a defective one, or that the gene simply accumulated mutations during our evolutionary history, leaving us dependent on dietary sources of a vitamin our ancestors once produced for themselves?

We could fill an entire book with the design flaws of the human body, each one a testament to our evolutionary history. In fact, biologist Nathan Lents has done exactly that in his excellent book Human Errors. I highly recommend giving it a read. But we need not belabor the point here; the evidence is already overwhelming. The human body is not the product of intelligent engineering but an evolutionary patchwork of inherited features, makeshift adaptations, and compromises accumulated over millions of years. It’s why your bodies attack themselves (autoimmune disease), grow malignant tumors, and necessitate yearly trips to the doctor.

So let’s move beyond the obvious. The human body is a product of evolution, and the mind is no exception. Our brains, after all, are organs too, shaped by the same evolutionary forces and subject to many of the same compromises, constraints, and imperfections as the rest of our bodies. Evolution doesn’t stop at the neck.

And it is these evolutionary inheritances—our cognitive biases, tribal instincts, emotional drives, and moral intuitions—that lie at the heart of the human condition. They help explain not only how we think and behave, but also why our efforts to build a more rational and humane world are so often frustrated. These are the questions we’ll explore in Evolution and Human Nature, a new section devoted to understanding the ancient evolutionary forces that continue to shape—and sometimes undermine—our modern lives.

Further Reading

Nathan H. Lents — Human Errors: A Panorama of Our Glitches, from Pointless Bones to Broken Genes