Given how evolution favors traits that lend themselves towards survival and reproduction, why are there still billions of people with near- or farsightedness?
I know I can’t see much of anything without my glasses, much less be able to survive half-blind in a more primitive world. Since corrective lenses are a relatively recent invention, how did the various poor-eyesight genes not get phased out by evolution ages ago?
I can’t help thinking about the old joke about the two men who are being chased by a bear. One of whom says “I don’t have to outrun the bear, I just have to outrun you”. What if 10% of your population is potential lion chow. That gives the other 90% an advantage over being in a group where everyone is at the same risk of being eaten.
Well sure, there are lots of disabilities that only a small bit of the population suffers from, but a large fraction still can’t see properly.
Well, in even fairly primitive societies, mild near or farsightedness probably wasn’t THAT big a deal. Even tribes would protect each other, and it’s not like tigers and such dug pits and hid behind rocks. They have some natural camouflage, but if your vision is only a bit blurry you’re still going to be able to see things like that. So I can see how some people who didn’t have perfect vision survived very early on.
Then, as society progressed, it allowed for further and further deviation for perfect sight, culminating in the evolution of me, who can’t see anything further than 3 inches from my damn pupil. Hooray for evolution!
Besides, the Chinese figured out lenses in like 500 BC or something like that, didn’t they? They just withheld them from the dirty foreigners for awhile.
Seeing as things that strain eyesight, such as reading, writing, and staring at computer screens all day, are still relative newcomers along our evolutionary trail – perhaps natural selection just hasn’t had time to catch up with the trend yet?
Do you have a cite that there is such a thing as ‘eyestrain’ and that it causes acuity problems like near and far-sightdeness? IOW, has the incidence of these problems become more common in modern times, or were they just undiagnosed before?
Are eye problems passed down by genes? I thought they were more of a physical problem. My shortsightedness began after puberty, but my mother was born with eye trouble.
There are more eye-problems causing visual loss than just near and far-sightedness, and many are inherited…and some don’t appear until after a certain age either (ala, puberty for shortsightedness, and early 20’s for primary glaucoma, and later ages for macular issues etc).
My eyesight is pretty bad… I can’t drive or see TV without glasses, and I strain to read fine print without them.
All of which would not necessarily limit me in pre-historic times. While my visual acuity isn’t that great, my field of vision, and ability to detect motion in that field, are probably somewhere in the normal range.
I suspect I could rough it in a pre-historic life cycle with only a very mild disadvantage vis-a-vis someone with 20/20 visual acuity. Which one of us would survive to produce more offspring would likely be a question of chance, or of some other limiting trait in one of us.
So, basically, bad eyesight (within limits) probably just didn’t matter that much…
That’s not what **Ice Wolf **was saying at all. Until a few centuries ago, most people didn’t need razor-sharp eye sight. They didn’t have books and computers and tv and traffic signs to contend with for hours every day. And people with poor eyesight would probably shy away from activities where good eyesight was a factor; but all they had to do was stay alive long enough to procreate.
Just expressing an opinion, kambuckta, that some factors which do affect (ie. worsen) eyesight are relatively new in terms of the total amount of time the species has been around. Sorry, I wasn’t carrying a notebook around when my various optometrists since I was 9 came up with such stuff for your cite. The increases in lens strength over the years has fluctuated depending on how much close work I do. Right now, there’s a lot of that.
Eyesight problems are inherited, yes. I get mine from my mother. But from what my optometrist said last time, eyes also change with age – and increased lifespans is also something relatively recent. My astigmatism is due to age, apparently.
Cheers, panache45.
Here’s some intriguing thoughts on the topic.
Dunno much about the guy who did that site, but – diet as a factor? Gotta admit, that’s interesting.
Many studies show a correlation between myopia and amount of time spent engaged in “near-work” – i.e. reading, drawing, using a microscope, etc. It can be difficult to differentiate cause and effect in these studies. Nonetheless, genetics is still the most influential variable – we learned in class that the greatest risk factor for the development of myopia in a child is having two myopic parents.
(Personally, I think the variable that correlates most highly with myopia is being a student in optometry school. Something like 95 percent of my classmates are myopes.)
So, like with most attributes, there are both environmental and genetic factors, which I guess isn’t very surprising.
Just a WAG, but I think that is because almost all people with eye problems serious enough to not be able to find food, or to outrun a predator, develop them after age 13 or so when they would have reached the age to reproduce.
My wife is an Optometrist, and this is what she was taught in school. So not exactly a site…but it’s what the old Doctors are teaching the young Doctors. She recommends you follow the rule of 20s when doing things up close, every 20 minutes look 20 feet away for 20 seconds (or is it the rule of 15?). Something about accommodation issues.
I remember reading once something about how leaving a baby in a crib or baby bed for too much of the day can cause problems with vision and balance. The problems develop before the age of about fifteen months and include sometimes the loss of much of the vision in one eye and not ever developing a secure sense of balance. Do any of you have more information on this?
Also, who’s to say what “perfect” vision is? We could have 20-20 or 20-10 vision but still envy the ability of an eagle.
My wife and I (both myopes) were rather surprised when our 14 year old daughter was diagnosed long-sighted. Three years on, she has just had an eye test, and her vision is near perfect.
We told her to enjoy the next few years - she will be myopic in a couple of years, and back to wearing glasses.
Si
Most eye problems manifest themselves in adulthood, right?
Evolution doesn’t give a damn about you once you’ve passed genes to a new generation. Evolution doesn’t care about enlarged prostates or arthritis or cancer, because people who typically suffer from these conditions have already had a chance to donate their genes.