This question already has an answer here:
- Bad Eyesight and Evolution 4 answers
Poor eyesight might have been a major impediment to survival and reproduction in early man (say, 100,000 years ago), but, with the advent of agriculture, major cultural changes, and modern medicine, one might imagine that genes for poor eyesight would persist more easily.
Is that true? Has selection on eyesight been relaxed, or changed significantly, in modern humans? If so, when? Do we know what might explain relaxed selection? If there are any genes associated with, for example, myopia, has their population frequency increased through human history, or has it remained constant?
This New York Times article discusses genetic changes 8 to 4 thousand years ago related to skin color, amino acid absorption, and eventually milk digestion, but it does not mention eyesight.
Background on why I find the question interesting:
A friend of mine speculated that human eyesight is worse today than it was only a few centuries ago, due to the invention and widespread adoption of glasses: a person with poor eyesight genes will now survive and have children, whereas in 1600 they might have died without reproducing.
I'm skeptical: first, glasses became widespread only a few generations ago; second, blurry vision plausibly has little effect on evolutionary fitness. I see no reason why someone with slight myopia would on average have significantly fewer offspring than someone with 20/20 vision, even in a tribe of hunter-gatherers. A short-sighted person could specialize in making hand-axes, for example, and trade them for food -- so I find it plausible that eyesight-related allele frequencies have not changed much over time.
However, I recently heard someone on the radio speculate that eyesight might have worsened significantly a few thousand years ago with the invention of agriculture; the story is that above-average eyesight is a major fitness advantage for a hunter, but not for a farmer. What does the evidence say?
Side note: I realize that eyesight is affected by more than just genes -- for example, age as well as time spent reading books probably both affect eyesight. That's not what this question is about -- I'm interested in genetic selection.
Edit: this question is indeed similar to Bad Eyesight and Evolution, but it isn't identical. That question asks why poor eyesight can persist at all, while mine asks whether evolutionary pressures have changed over time. In particular, do we know of any genes associated with, say, myopia? Do we know whether their allele frequencies have changed over human history?