Re: Why don't animals need glasses?
- From: r norman <r_s_norman@xxxxxxxxxxxx>
- Date: Sun, 30 Sep 2007 16:50:31 -0400
On Sun, 30 Sep 2007 15:22:36 -0400, "Daniel T."
<daniel_t@xxxxxxxxxxxxx> wrote:
dkomo <dkomo871@xxxxxxxxxxx> wrote:
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.
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.
(Aren't explanation 2 & 3 basically the same?)
I expect that all three explanations have something to do with it. For
another example, read up on asthma. As we find cures, the asthma rate
(as a percentage of the population) is increasing dramatically. Some,
maybe even most, of the increase is probably due to environment, but not
all.
As is usually the case, bringing in facts merely confuses the issue.
The major problem of myopia is that the eyeball grows too much in the
axial (from lens to retina) dimension. The growth of the eye is
regulated by both genes and experience. Many animal experiments with
defocusing the eyes using external lenses have demonstrated that there
are retinal feedback mechanisms controlling eye growth. That is,
there are physiological mechanisms that can produce abnormal growth on
the basis of use (or disuse). There are also genetic studies
indicating a clear genetic factor for myopia with rather high
heritability implicating at least on at least four chromosomes. Still,
there has been a really significant increase in myopia in recent
decades in industrial societies both Eastern and Western and that
can't be attributed to evolutionary shifts in gene frequency. I have
seen a suggestion that sustained near work with high cognitive demand
is an important factor, one that accords with both the observed growth
in myopia and the known physiological mechanisms to have eye growth
regulated to adjust particularly for near vision.
.
- References:
- Why don't animals need glasses?
- From: dkomo
- Re: Why don't animals need glasses?
- From: Daniel T.
- Why don't animals need glasses?
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