Assuming that long/short sightedness is hereditary why hasn’t natural selection ironed it out of the gene pool?
Eg. Short sighted hunter doesn’t see the tiger until it’s too late, gets eaten and doesn’t pass on the genes.
Thanks and apologies if this has already been asked.
IIRC, James Burke explained that the amount of reading we do in school & life causes near sightedness (far sightedness??). Cultures that are newly introduced to universal education also have a jump in eye problems because focusing on the same distance all the time is bad for your eyes. I can’t recall which book that is in.
Because before the 20th Century no one defined “bad eyesight” as “anything other than 20/20”
Seriously, we slapped a precise number on an organic sensor. So someone with 20/25 or 20/30 could be said to have “bad eyesight” (i.e. “less than perfect”) when the reality is that in day to day life someone with 20/30 functions just as well as someone with 20/20. In fact, as far as I know in all states in the US 20/40 vision does not require glasses to drive a car, and the FAA allows private pilots with 20/40 vision to fly airplanes without using glasses. Obviously this is not much of an impairment
Also, someone slightly farsighted could be said to have “poor vision” these days (and reading might difficult without glasses), but 200 years ago being slightly farsighted might be advantageous. Certainly, before things like binoculars and telescopes were invented or common a farsighted person might find gainful employment as a lookout of some sort. It wasn’t seen as “bad eyesight”, it was seen as an asset.
So, in part, it’s a result of a very very narrow definition of “normal vision”.
There are also theories that the heavy emphasis on reading our culture imposes on young children also affects their eyesight in a detrimental manner. Cecil has mentioned this in a prior column, which I couldn’t find this morning in order to link to it.
Also consider that, in the bad old days, people with REALLY bad eyesight really were functionally blind and really did have serious survival issues. We have more people with bad eyesight these days because it’s a survivable disability now that we have invented eyeglasses and contact lenses.
With the development of corrective lenses, there has been no reason for near- or far-sightedness to be selected against. It’s no longer an obstacle to survival. Just as most Inuit are hairless despite living in a very cold climate – the existence of warm clothing makes hairlessness a neutral trait with no reason to be eliminated from the gene pool.
To survive as a species, we really only needed decent eyesight until some of our key reproductive years, and then the importance of it became less of an issue in terms of passing your genes to the next generation.
Many problems that start to afflict people as they age are related to this evolutionary issue: bear children…spread you genes, and you are succesful. Everything after that is moot. Life expectancy has increased greatly, but it was so short centuries ago that bad eyesight affected few people, since so most people were ‘young’ by our standards.
Surely though people that can see unaided perfectly far, medium and close distance have the proper vision that Nature intended? Particularly as most long-sightedness comes on with old age, it is CLEARLY a deviation/deterioration from the norm.
My personal thought is that because bad eyesight is not a physical disability that makes one unattractive - ie it is not particularly noticeable to other people - it has never got bred out of the genepool.
And since humans found fire and shelter and other ways to protect themselves against wild animals (and other humans), the cavemen Mr Magoos were probably more likely to survive.
And undoubtedly modern living contributes to eyestrain and it would appear myopia, from so much close work, artificial and poor light, and overuse of eyes.
I speak as someone extremely shortsighted/myopic.
I’m reading a book right now on repetitive strain injuries, and they have a section on vision. They claim that research shows that we most likely develop vision problems because of an emphasis on close work (the eye muscles get fatigued by repetitively focusing on books, computer screens, etc.). They cite a study of a community of Eskimos with traditionally very good eyesight. When the Eskimo children attend traditional schools for the first time, they develop vision trouble in proportion with “industrialized children”. The only cite they give is the book “Improve your vision without glasses or contact lenses: A new program of therapeutic eye exercises” by Steven Beresford, 1996.
I would guess that the authors here would claim that even if genetics gave us some predisposition to vision trouble, our behavior is most responsible for the damage. I’m not sure that I would completely agree with this (what about children with vision trouble very early on?), but it is one viewpoint.
My (uninformed) theory is that bad eyesight is a product of living in cities.
Before we lived in cities our eyes would naturally tend to focus on the horizon but since the industrial revolution and the mass movement to the cities our eyes now only focus on the other side of the street. This is unnatural and means our eyes our constantly having to strain to focus on a point closer than God intended.
I try to gaze at horizons as often as I can because I think it relaxes my eyes although it’s possible this is just psychosomatic.