The Perfect Eyesight of Hunter-Gatherers

In modern, industrialized nations such as the United States and Norway, where I live, it’s the norm rather than the exception to have suboptimal eyesight. A lot of people are either near or farsighted, and many also develop cataracts and macular degeneration as they get older. These conditions are so common nowadays that having issues with one’s eyes and vision is sometimes considered a natural part of being human.

What’s frequently overlooked is the fact that most of our evolutionary journey took place in a natural environment and that our ancestors needed to be able to see clearly in order to survive, and eventually reproduce. This is important to note, because it implies that the eye-related problems that plague the modern man aren’t necessarily intrinsic to the human condition, but rather develop as a result of a gene-environment mismatch. Indeed, modern hunter-gatherers appear to have excellent eyesight (1, 2). There’s no reason to think that the situation was any different in the distant past.

Why do hunter-gatherers have such good eyesight?

An answer to the above question quickly presents itself when a dose of Darwinian logic is added to the equation. Hunter-gatherers need good eyesight in order to track down animals, locate wild, edible plant foods, evade dangers, and otherwise survive in the natural environment in which they live. A myopic hunter-gatherer would be at an obvious disadvantage in the struggle for existence. He certainly wouldn’t be favored by natural selection.

Given that this is the case, it’s not surprising that myopia, as well as other similar eye-related conditions that compromise survival under natural conditions, are rare among people living under conditions that resemble those under which our ancient hunter-gatherer forebears lived.

Why do modern, industrialized humans have such poor eyesight?

This question is somewhat more difficult to answer. It’s clear that myopia and many other eye-related disorders develop largely as a result of evolutionary mismatches: the relevant genes have been around for a long time; however, it’s only recently that they’ve started becoming problematic. What not perfectly clear is what types of mismatches that are the most important in this respect. There’s no general consensus among Darwinian researchers. Many explanations and theories, some better than others, have been proposed.

Personally, I’m inclined to think that the main reason why the modern man has such poor eyesight is that he spends many hours every day staring at a computer or phone; an explanation that it very much scientifically sound (2, 3, 4). Just like any other organ, the eye changes in response to the stimuli it’s exposed to. Not that unlike a muscle that grows more powerful or larger in response to strength training, the eye modifies itself in accordance with how it’s used.

Given that the body, including the eye, is so malleable, it’s not surprising that the functionality of the human eye changed as we humans transitioned over from living in the wild to eventually spending most of our wakeful hours staring at a light-emitting screen a few feet in front of us. By using lenses/glasses, we’re able to correct some of the complications that arise as a result of frequent, prolonged near work. Unfortunately though, this practise may initiate a vicious cycle and make our eyesight worse over the long-term, as explained below:

If myopia is an adaptive physiological response to prolonged near work, correction of myopia with lenses during childhood may increase the final degree of myopia by requiring further adaptive changes in axial length to neutralise the effects of the lenses. Certainly in animal studies minus lenses do result in ocular growth towards myopia. Whether this implies that myopic children should be undercorrected remains controversial. (5)

I’m also convinced that nutrition plays a role up in all of this. I don’t think it’s as important as what I talked about above; however, there’s no doubt that the food we eat does affect our eye health. Hunter-gatherers don’t eat junk food, cereal grains, or dairy products and they take in a lot more phytochemicals and fiber than we do. In particular high-glycemic, insulinogenic foods appear to be problematic in this regard, as they have been shown to alter the growth of the eye via their hormonal effects (2). This helps explain why the eyesight of hunter-gatherers is a lot better than ours. Basically, they give their eyes what the human eye evolved to need in order to function well.

Can we remedy the situation?

In the evolutionary health community, a lot of attention is devoted to how we – contemporary humans – can resolve the many evolutionary mismatches that lie at the root of the diseases of civilization. Typically, the solution involves adjusting one’s lifestyle so that it more closely resembles that of a hunter-gatherer. That’s often easier said than done though. This is particularly true when talking about the environmental factors that drive the development of conditions such as myopia.

A lot of people use a computer at work and can’t simply choose to not read or use a computer at all – and even if they were to stop working altogether and move into the wild, that wouldn’t necessarily mean that their eyesight would become perfect, seeing as it’s generally a lot more difficult to correct a problem once it’s developed than to prevent it from developing in the first place. Moreover, epigenetic factors may be at play up in all of this.

That said, it’s obviously possible to limit or restrict one’s screen time. This could positively affect one’s eye health. Moreover, anecdotal reports indicate that some people have been able to partly or fully correct myopia by gradually adjusting the distance at which they read books and view their computer screen and/or by altering the strength of their lenses over time. Personally, I’ve never gotten around to adopting and sticking with such a routine; however, seeing as I’m myopic, it’s something I would definitely like to try one day.

When it comes to nutrition, as well as sun exposure, sleep, physical activity, and the like, it’s usually easier to bring about change. By eating healthy, taking care of one’s friendly gut bacteria (the gut microbiota has a long reach, and has been shown to affect the health of the eyes (6, 7), avoiding exposure to artificial light late at night, and spending plenty of time outside, thereby exposing one’s eyes to a lot of natural light (this has been shown to be favorable in the prevention of myopia (8, 9, 10), one maximizes the likelihood that one’s eyes function well – and continues to function well for a long time.

Pictures: 1: Creative commons pictures by Ian Beatty. Some rights reserved. 2: Creative commons picture by Thiery. Some rights reserved. 3: Designed by Freepik.