Most of my life I've wondered what would have happened to me if I had lived in a time before eyeglasses. I'm pretty nearsighted. Without glasses, anything more than a few feet away starts to get blurry. Which would have been a serious problem for most of human history. If I had been born thousands of years ago, would I have been able to hunt? Would I see an animal before it saw me? Would some predator emerge from the blur and eat me? And if bad eyesight was that much of a disadvantage, why didn't evolution eliminate it?
Turns out our ancestors generally weren't nearsighted. At least not anything like we are today. Myopia is relatively uncommon in hunter-gatherer populations. And researchers have watched it increase dramatically when populations move indoors, enter schools, and adopt modern lifestyles. In some indigenous arctic communities, myopia went from almost non-existent to affecting more than half of younger generations within a remarkably short period of time.
Today, researchers have also found that children who spend more time outdoors are less likely to become nearsighted, even when you account for genetics. Because your eyes don't simply arrive fully formed. They develop in response to the environment you put them in. When children spend more time outdoors, their developing eyes are exposed to levels of natural light they almost never encounter inside. Put those same developing eyes indoors for hours every day, surrounded by books, worksheets, and now screens a foot or two from their face, and you've radically changed the visual environment those eyes are developing in.
Which made me think about when I got my first pair of glasses. Third grade. Right around the age when school starts becoming much more about reading. I remember sitting in class and realizing I couldn't read what the teacher had written on the board. So my parents took me to the eye doctor. But no one ever asked why my eyes were becoming nearsighted in the first place.
Civilization can change our environment faster than evolution can prepare us for. We take an organ that developed in a world of sunlight, enormous distances, and constantly changing visual demands, put it indoors under artificial light, surrounded with things a foot or two from our face. And when the eye develops differently in response to the environment, we assume there's something faulty in the person.
Maybe there was never anything particularly wrong with my eyes. Maybe my eyes were doing exactly what eyes have always done. Adapting to the world they were placed in. Which finally answered the question I'd been wondering about all those years. Why didn't evolution eliminate nearsighted people? Because for most of human history, many of us who wear glasses today probably wouldn't have needed them.
