Misc. questions on the biological history of eyesight problems.

May 28, 2004 4:29 AM

Have we always had poor eyesight? I know, of course you are going to exclaim "yes!", but in the days of people not having glasses, shouldn't natural selection have weeded out people like me? How did we cope without vision correction, from an objective viewpoint?
posted by Keyser Soze to Science & Nature (30 answers total)

Oddly enough, relaxing on the couch with a good book wasn't very high on the priorities list for homo erectus.

Basicly, getting eyes that are guaranteed not to get fucked up during body formation would cost more resources than its worth. Unless your eyesight is really bad, your hunting/gathering skills should still be within a few percent of those of someone with average vision.

Of course, there might be an eye design that is much better but not resource-expensive, but evolution hasn't found it yet.

Evolution takes an infinite amount of time to find the optimal creature for a certain environment, or possibly even that isn't enough. But that's more of a mathematical issue.
posted by fvw at 4:45 AM on May 28, 2004

FVW's argument is the one I've heard. Nearsightedness is an offshoot of the very necessary ability of your eyes to adapt to correct.

Evolution seems to do remarkably well with substantially less than infinite time. I am always surprised how optimal evolution gets, especially given time.
posted by rudyfink at 4:53 AM on May 28, 2004

Life was harsh and the value of life wasn't what it is today. The value of life wasn't even that of today a couple hundred years ago. It was common to abandon infants with obvious health problems (which nearsightedness wouldn't be seeing as babies are born fairly blind) so I don't think there'd be much of a problem with abandoning a nearsighted person either.

On average good eyesight might have been less common then since it's possible that those with really poor eyesight might be weeded from the genetic pool before they took a dip. If your eyesight isn't too poor you can get by with squinting for some tasks. Your eyesight can be a lot poorer as even a hunter than you think if you don't have a firearm. Rocks, spears and bows and arrows have fairly limited range compared to even a cheap 22 caliber rifle.

As life became less harsh there would be more things for people to do with poor vision. You can grind grain, weave etc.
posted by substrate at 5:09 AM on May 28, 2004

I think our ancestors had other skills and attributes that made them worth keeping around the tribe/clan/pack/etc, whether brain-wise or skills-wise or looks-wise or something. Also, other people would have watched out for us, I think. (Like what substrate said, but i think we were kept around even earlier than farming or weaving started)
posted by amberglow at 5:14 AM on May 28, 2004

Response by poster: How ironic the value of life has increased proportionately with the increase of life.

"getting eyes that are guaranteed not to get fucked up during body formation would cost more resources than its worth."

Forgive my naive interpretation of evolution, but since (at least in Oregon, USA) we are given a near excellent place to be born, be fed food, and recieve proper care, why wouldn't our bodies focus on formating the "perfect" eye?
posted by Keyser Soze at 5:17 AM on May 28, 2004

Response by poster: Ok, formating is not a word. Forming?
posted by Keyser Soze at 5:18 AM on May 28, 2004

I read a theory somewhere that the cavemen with the poor eyesight had to stay home and guard the cave while the other menfolk went out hunting. The cave-women, sitting around bored after picking berries for a few hours, proceeded to take advantage of these left-behind cavemen and shortly thereafter gave birth to poor-sighted babies...
posted by Gortuk at 5:35 AM on May 28, 2004

I'd buy that theory, Gortuk. Also we could have been in on the hunts but stayed in the back to help harvest the bodies and carry them back to the cave/whatever.
posted by amberglow at 5:45 AM on May 28, 2004

Consider also that our ancestors started having babies when they were in their mid-teens and shortly after fleeing mama's protective wing. Evolution is not about adult abilities, but surviving childhood.
posted by mischief at 5:54 AM on May 28, 2004

Also, the short sighted cave people could breed with the uglies.
posted by biffa at 6:01 AM on May 28, 2004

Someone - was it Aldous Huxley? wrote a book on improving one's vision. His theory was that glasses are a crutch and only make the eyes weaker and that eyes can be exercised and made stronger thereby. There may be something in that.
posted by orange swan at 6:12 AM on May 28, 2004

Keyser: You can't really expect evolution to sit up and take notice of that last handful of generations (or probably less) that had all the food they needed provided they were at least marginally capable of work.

biffa: I applaud your creativity in this matter, but alas not breeding with the uglies if there's something better you can get is an evolutionary pro.
posted by fvw at 6:13 AM on May 28, 2004

KS: Why isn't evolution directed?

Because (unless you accept the devine), evolution has no intention. There's no biological endpoint that our bodies are evolving toward. Evolution works by accident.

Maybe a kid will be born with a more perfect eye than yours or mine. Will her kids have more kids than yours or mine? If yes, then more humans in the future will have better eyes. If no, then better eyes don't matter.
posted by bonehead at 6:16 AM on May 28, 2004

Two thoughts:

(1) A number of genes or sets of genes which code for otherwise "undesirable" traits are linked to other genes which code for "desirable" traits. If the benefits to fitness of the desirable traits outweigh the impact of the undesirable traits, the undesirable traits will propagate and survive right alongside the desirable ones. One way this can occur is chromosome linkage.

(2) Another explanation which avoids evolutionary explanations entirely: deterioration of eyesight is not in all cases an inheritable trait. Some eyesight problems are thought to be genetic, but not all. If poor eyesight is caused by, in at least some cases, embryological factors or other environmental factors later in life, and not genetic factors, then evolution won't have much of an impact on those non-genetic causes of those traits.
posted by monju_bosatsu at 6:19 AM on May 28, 2004

Hello! - this question concerns phenotype as much as it does genotype :

"Children who read more than 2 books at week are at greater risk of developing short sighted vision than those who read less, according to a large study being presented at the XXIXth International Congress of Ophthalmology in Sydney this week.

Researchers at the National University of Singapore and Singapore Eye Research Institute have been studying 2000 children aged from 7 to 9 for the past 2 years.

They found that children who read more than 2 books a week were 3 times more likely to develop myopia (short sightedness) than those who read fewer books.

They also found that children with the same reading patterns were 10 times more likely to develop myopia if both parents suffered from it.

People who have myopia have poor distant vision and objects appear blurred. They tend to squint if the myopia is left untreated. Their near vision is usually not affected although it can deteriorate with age.

Head of Epidemiology at the Singapore Eye Research Institute Assistant Professor Seang Mei Saw said that the interaction between genes and the environment was significant in increasing people's risk of myopia.

She said the message for parents was not to limit the time children spent reading, but to be more vigilant with eye testing, particularly if there was a family history of myopia.

Assistant Professor Seang Mei Saw said that 'near work' activities, such as reading and computer use, contributed to the development of myopia. Poor night lighting was also an issue.

Incidence of myopia is high in developed countries such as Australia, which have a strong focus on education."

Google search - "myopia,childhood,reading"

So - you could blame civilization, I suppose.
posted by troutfishing at 6:30 AM on May 28, 2004

[ as well as genetic factors ]

The reading/myopia theory exactly fits my family : among my siblings and myself, the two heavy readers during childhood now wear glasses full time for myopia. One moderate level childhood reader has slight myopia but rarely wears contacts or glasses for vision correction - it's just not enough of a problem. One sibling who read only occasionally has good vision.

I recall encountering this explanation - the shape of the eye develops to some extent during childhood, and so heavy childhood reading encourages the development of an eye shape specialized for close focus.

Over time, for many, myopia can gradually self correct. The general tendency, with age, is for a gradual shift towards farsightedness. This is curiously fitting.
posted by troutfishing at 6:42 AM on May 28, 2004

I met someone trying the Huxley vision-improvement a few months back. He was getting mixed results: His vision had improved a bit, but unfortunately his glasses were rendered useless in the process. So he couldn't see slightly better than before.
posted by kaibutsu at 7:04 AM on May 28, 2004

You'd be surprised at how much your other senses sharpen when you can't see well. I've gone without my glasses for periods of months in the past, and I found myself much more aware of noises and smells, not to mention my brain interpreted my poor vision input in different ways. For example, I became incredibly good at recognizing people from a distance based upon their posture or their gait and way of walking.

I have this persistent neurotic side of me that occasionally obsessively wonders what we would do if modern civilization collapsed and technology went with it. It's an unlikely scenario, but what if all the glasses and contacs in the world no longer existed? I suspect that the adaptations and ingenuity required by blurry vision, despite its obvious disadvantages, might even be a net advantage in survival, including hunting, self-defence and warfare.
posted by Shane at 7:09 AM on May 28, 2004

It's true that what might be mildly defective vision is made much worse over time by the use of glasses.
posted by IshmaelGraves at 7:30 AM on May 28, 2004

If I recall correctly from my introduction to evolutionary theory class, needing glasses has very little to do with genetics. Supporting evidence included a comprehensive longitudinal study of an Alaskan native village, starting from well before there was any written communication (100% illiteracy). At that point, there was nearly no need for glasses. (Nearly 0%) Starting with the advent of writing and books being introduced to the village, the need for glasses steadily grew, until literacy was hovering in the high 90%, and the need for glasses was a few percentage points behind: the relationship was almost perfectly linear. Likewise, there is the common-sense notion that having spectacularly bad eyesight (as many people in this modern age do) would prove to be less than advantageous in the survival derby, and should, if genetically inherited, decrease in gene frequency.
posted by Eldritch at 7:45 AM on May 28, 2004

I think you can look at the makeup of modern armies and compare them directly to a hypothetical hunting party of long ago.

Basically, you'd think if you can't see an animal and aim well enough to kill it, you probably wouldn't have survived, but look at modern armies. Not everyone is a sniper. A select few marksman are chosen because of their abilities and pushed to the front to do their magic, while the rest protect them. You could likely see the same thing in a hunting party of say, 10 guys. Probably 2 or 3 had great eyesight and coordination and probably were the lead hunters, while the rest were there for protection and support. Also, even in ancient times, those with poor eyesight would have made fine farmers or even gatherers.

I agree with previous comments here that reading small print in the last few generations probably has the most to do with the wide use of glasses today.
posted by mathowie at 11:06 AM on May 28, 2004

I can barely see a hand in front of my fiace without my glasses on. If I tried to go without them long enough to hone my other senses, or to try some vison-improvement technique, I would definitely die of some serious fall or collision with a heavy object. It wouldn't take long.

Also, I read a lot in my childhood, but so did my younger brothers, one of whom has only started to need glasses occasionally in his late twenties, and the other (who has been looking at computer screens since he was six), has perfect vision.
posted by bingo at 11:47 AM on May 28, 2004

Obviously cave-bingo would have died, but most people would have just watched his blurry body fall off a cliff and made a note to avoid that area.
posted by dness2 at 1:11 PM on May 28, 2004

My pet theory on this subject is that the increase in poor vision is a fairly recent development - the result of the hours younger people now spend in front of their TV & computer monitors. My anecdotal evidence is that neither of my parents nor my wife's parents wear glasses even in their 50's and 60's, none of our eight grandparents wore glasses until they were retired. My wife and I both got our first sets of glasses while we were still in high school.
posted by Jaybo at 1:26 PM on May 28, 2004

Response by poster: I was engrossed in books all the time when I was young, and I am engrossed with computers as an adult. This eyesight thing doesn't surprise me.
posted by Keyser Soze at 3:36 PM on May 28, 2004

I think if it was totally environmental, far more people would be nearsighted, and everyone that uses a computer all day would be. I know I come from a long, long line of 4-eyed people, so I'll stick with the "we had other talents" theory.

'-O-O-'
posted by amberglow at 4:46 PM on May 28, 2004

'-O-O-'

- I'm stealing that - it matches (".) nicely!
posted by dash_slot- at 5:19 PM on May 28, 2004

remember also that a disability that happens when you're 25-30 has been meaningless for most of our evolution, as you wouldn't have survived much longer than that anyway. Also, eyesight is very environmentally dependent, as people said. Also, humans didn't have to read, they just had to be able to find food, and avoid big animals.

linkage is unlikely, if you accept that the "bad eyesight" gene is significantly detrimental linkage is not a strong enough force to keep it in the population. linkage does occur, but our genes undergo recombination quite a bit. it explains things like freckles and red hair, but if freckles were bad for you and red hair good, we would just lose the freckles.

More likely our vision impairment either isn't as bad as it seems evolutionarily, either because it's environmental, or because people died of other causes before it mattered.
posted by rhyax at 10:00 PM on May 28, 2004

So basically, the whole stereotype of people who wear glasses being smarter is true if you buy, as I do, the theory that reading as a child makes you blind. That would also explain why it looks genetic - children who read a lot are more likely for environmental reasons to have parents who read a lot.

Also, I guess my mother was right to yell at me for reading under the covers. Too bad I didn't listen.

"Why Miss Jones, you're BEAUTIFUL!"
posted by CunningLinguist at 6:38 AM on May 29, 2004

there are no muscles in your eye to make you see things in the distance, only muscles to help you see things close by. in theory, the lens in your eye focuses at "infinity" when relaxed. when you want to focus on something closer, muscles squeeze the lense to change the shape. when you want to return to looking at something further away the muscles relax and the lens bounces back to its default shape.

short-sighted people have a lens that is already focussed at a point closer than infinity (the lens is too strongly curved for the eyeball shape). they can focus closer by squeezing the lens with the appropriate muscles, but no matter how much the muscles relax, they cannot see things in the distance properly because when the lens "goes back" to its normal shape, it is still not "good enough".

so it's not possible, if that is correct, to train your eyes (as an adult) in a way that cures short sightedness.

this is why the reports above of children reading books and becoming short-sighted mentions development. it appears that the lens (or eyeball shape) is still developing as a child, and the "correct" shape becomes distorted.

as you get older, the lens becomes more rigid and/or your muscles weaken, so focussing closely becomes more difficult. with age, therefore, people tend to become longsighted. but this cannot correct for short-sightedness. it simple reduces the range over which you can focus - it doesn't extend it to longer distances that you couldn't focus on before.

that, at least, is what i understand of eye conditions. no idea where i learnt it from - perhaps my optician. it is supported by the information here.
posted by andrew cooke at 7:56 AM on May 29, 2004