In the column asking about bad vision caused by sitting too close to a TV or reading in dim light: http://www.straightdope.com/classics/a5_105.html
It was mentioned that some people have suggested that there is something about civilization that causes nearsightedness, and an eskimo population study was brought up. I realize that the study was called into question for not being random, but there are other options. It ocurred to me that prior to modernization, those with myopia might not live as long as those without. As my wife is fond of saying, with no glasses around, she would have been eaten by a sabretooth while she was young. Note that the 59+population segment had 0% myopia in the study.
Just my $0.02!
-Tiki