Re: Why don't animals need glasses?

On Sep 30, 9:55 am, Ron O <rokim...@xxxxxxx> wrote:
On Sep 30, 11:32 am, dkomo <dkomo...@xxxxxxxxxxx> wrote:



Actually, this is a teaser question brought on by ruminating on the idea
that if human beings had to rely on their eyesight to survive today, as
we did in our hunter gatherer days, our population numbers would be far
less than they are.

Here's an amazing fact:

"The global prevalence of refractive errors has been estimated from 800
million to 2.3 billion.[20] The incidence of myopia within sampled
population often varies with age, country, sex, race, ethnicity,
occupation, environment, and other factors.[10][21] Variability in
testing and data collection methods makes comparisons of prevalence and
progression difficult.[22]

In some areas, such as Japan, Singapore and Taiwan, up to 44% of the
adult population is myopic."

http://en.wikipedia.org/wiki/Myopia

What can explain the loss of good vision in our species? Presumbably at
one time vision must have been quite important to our survival, as we're
not gifted with keen hearing or smell as other animals are. If another
species which used to rely on vision to hunt or escape predators started
to develop vision problems as prevalent as ours, it might go extinct
because it would have no way to correct these problems like we do.

Do animals develop myopia? It's probably difficult to test for this.
I'm not aware of any experiments that have been done.

Possible explanations for the spread of human myopia:

1. Reading brings it on.

2. We don't need keen eyesight for hunting anymore, so mutations in
genes that control vision have caused a weakening of eyesight in our
species.

3. In prehistoric times, people with myopia would have been eliminated
from the population by natural selection. Nowadays, wearing glasses
allows people with myopia to lead normal lives and to have offsping,
causing genetic defects producing myopia to spread.

--dk...@xxxxxxxx

There could be environmental factors, but my first guess is that it is
like blind cave fish. Our eyesight only has to be good enough to
survive. Even for hunter gatherer bands there was likely a
distribution of labor. Nearsighted members might not be the best
hunters, but they could set snares, do close in gathering, baskets,
nets, etc. and close in detail work would suit them. These people
might not have been able to use a bow, but they could make one.

Eyes are expensive to maintain. A lot of traits have to be selected
for and against. There is slop in the system, but eyes are one of the
first things to go if they aren't needed.

Ron Okimoto

I concur, kind of. Especially after the beginning of the neolithic -
farmers need decent eyesight ("where's the hut?") but not eagle-eyed
sharpness. As my daughter points out, 20,000 years ago she would never
have been born - her mother and I would never have lived to
reproduce.

The occasional nearsighted hunter-gatherer might live to adulthood,
but sooner or later his descendants would have to dodge an enemy's
spear, or spot the smilodon lurking behind a bush at night. I suspect
that myopia did not become prevalent until agriculture did, and
extreme myopia like mine, was a serious handicap until 100 years ago
(not all eighteenth century peasants could afford glasses). Maybe the
ones with brains were able to get jobs as scribes.

On the other hand, perhaps our modern genes give greater resistance to
plagues, or better interpersonal/political skills, both of which are
helpful in high-population density environments.

My old cat is a fine old girl, and she was born in a litter to a feral
cat in our garage. All of her genes were good cat genes. I'm sure. We
fixed her anyway ;)

Kermit

.

Relevant Pages

  • Re: Why dont animals need glasses?
    ... that if human beings had to rely on their eyesight to survive today, ... we did in our hunter gatherer days, our population numbers would be far ... one time vision must have been quite important to our survival, ... allows people with myopia to lead normal lives and to have offsping, ...
    (talk.origins)
  • Re: Why dont animals need glasses?
    ... that if human beings had to rely on their eyesight to survive today, ... we did in our hunter gatherer days, our population numbers would be far ... What can explain the loss of good vision in our species? ... Do animals develop myopia? ...
    (talk.origins)
  • Re: Why dont animals need glasses?
    ... that if human beings had to rely on their eyesight to survive today, ... we did in our hunter gatherer days, our population numbers would be far ... What can explain the loss of good vision in our species? ... Do animals develop myopia? ...
    (talk.origins)
  • Re: Why dont animals need glasses?
    ... that if human beings had to rely on their eyesight to survive today, ... we did in our hunter gatherer days, our population numbers would be far ... one time vision must have been quite important to our survival, ... allows people with myopia to lead normal lives and to have offsping, ...
    (talk.origins)
  • Re: Why dont animals need glasses?
    ... that if human beings had to rely on their eyesight to survive today, ... we did in our hunter gatherer days, our population numbers would be far ... one time vision must have been quite important to our survival, ... Nowadays, wearing glasses ...
    (talk.origins)