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Ask Marilyn: Nearsightedness and Evolution
Stu Lewis of Prairie Village, Kansas, writes:
Marilyn: I think there were some better answers you could have given about evolution and nearsightedness. (September 9, 2012) One could respond to your answer by asking why the body has not developed better defenses against this condition.
(1) Nearsightedness primarily affects one's ability to read. This became a survival skill relatively recently in human history, too recently to have been affected by evolution.
(2) This condition normally occurs later in life. Evolution affects only characteristics that appear before or during one's child-bearing years.
You imply that myopia also may have been common throughout human history, but because it didn't affect survival until recently, it hasn't been affected by evolution. I don't agree. Myopia affects the ability to see clearly what one holds in one's hands and what one does with one's hands, which has certainly been a survival skill throughout mankind's existence. And I don't believe that the ability to read standard-size print can be classed as a survival skill, regardless.
Also, nearsightedness usually begins in school-age children, then worsens gradually. You can read an American Optometric Association article on the subject. Possibly you're thinking of presbyopia, a condition that normally occurs later in life. Presbyopia is caused by the increasing inability of the lenses to change shape and focus on nearby objects. That's why nearly everyone needs "reading glasses" when they get older.