Why are we short-sighted?

SuperHans

Being short sighted myself, I often wonder how people survived in pre-corrective lens days. I can imagine myself stranded on a desert island without glasses and really struggling to get around the place effectively.
This begged the question in my mind: Surely early humans with bad eyesight couldn't function effectively and therefore over time(hundreds of years), these humans would have become more and more scarce until bad eyesight was not a major issue(ie. it affected only a small minority of humans).

A quick google suggested that bad eyesight is actually not genetic, and was not a major issue(in terms of the percentage of the population which had it) until modern times. It is apparently a uniquely human trait, and it is now believed that a starchy westernized diet is a contributory factor towards the phenomenon(if it can be called a phenomenon).

So can anyone out there who is well informed shed some light on the matter as to why we are short-sighted?

Here is the a link to the article that I read:
http://www.second-opinions.co.uk/myopia.html

I myself am a bit sceptical on it's validity as I don't think that it's particularly well written, so would appreciate other's views on it.

The_Minister

Because you touch yourself at night.





The idea of it being down to diet doesn't gel with the extremely high numbers of Asians who are short-sighted.

http://www.straightdope.com/columns/read/1107/will-sitting-too-close-to-the-tv-reading-with-bad-light-etc-ruin-your-eyes

You have to remember that even after millions of years of evolution, messed up kids are born to all species, every day. It's just that in the wild they die off, but we keep them alive. For example, near Chernobyl, in the danger zone, wolves have made a major comeback, because there are no humans to hunt them. Sure, some of their babies die from mutation, but many don't, and they just make more.

Sangre

I wonder if the reading/writing stresses the eyes a lot more than previous generations. Especially now with TVs and computers.

The_Minister

Sangre wrote: »

I wonder if the reading/writing stresses the eyes a lot more than previous generations. Especially now with TVs and computers.

Thats one of the longest standing theories, but doubt has been thrown on it recently.

doolox

Consider this.
Humans can reproduce at 12-13 yrs old and babies can usually scratch around for food at 4-5 yrs old so all a human had to live to was about 20 yrs if they wanted to continue their genes to the next generation.
In evolutionary terms therefore a 20-yr old human capable of avoiding danger and getting probably one meal a day would be considered a success.
Eyesight is only one of the five senses animals use to get by in their world and many animals have far worse eyesight than we have and still get along.
It is possible that the badly sighted humans carved out a niche in the early dawn of time, gather food in ways that did not require good eyesight. Probably better sense of smell, better hearing etc helped.
Modern ways of living, with its emphasis on taking in large quantities of highly detailed visual information, places a huge emphasis on good eyesight.
Outside of war and some sports, old lifestyles didn't.
Bad eyesight was there in the old days but simply wasn't recorded as such.
Chances are badly sighted people who chose to ignore their problem and go to war with clear sighted people were killed off. The others adopted other survival strategies, had babies and their successors are here today.

dresden8

Not to mention the family/social structure protected those without great eyesight, they could still do work.