[extropy-chat] why the vertebrate eye might not be suboptimal after all

[The Avantguardian]

--- Russell Wallace <russell.wallace at gmail.com> wrote:

> On 7/7/06, The Avantguardian
> <avantguardian2020 at yahoo.com> wrote:
> >
> > I agree with your friend, Damien. If ID were
> correct,
> > you would think that humans would have the best
> eyes
> > of all. We would have stable retinas with forward
> > facing photoreceptors and no blind spot. We would
> have
> > the night vision of cats, the distance vision of
> > hawks, the polarized vision of squids, and the UV
> > vision of honey bees, and a third transparent
> eyelid
> > like birds.
> 
> 
> While I don't know enough about the subject to know
> whether the advantages
> of the current arrangement cited actually outweigh
> the disadvantages (though
> I find it interesting that the matter appears to be
> debatable), there is a
> long-standing tradition of criticizing the work of
> evolution; what is
> interesting is that most of the time the error turns
> out to be on the part
> of the critics.

True. Most critics underestimate the resourcefulness
of natural selection operating on the scale of deep
geologic time.

> From the above list, for example:
> our night vision is
> inferior to that of cats because (or at least partly
> because) the layer
> behind the retina is black rather than reflective,
> but this cuts down on
> glare in daylight; we could see UV if our lenses
> were transparent to it, but
> the opacity is a feature rather than a bug, it helps
> protect the eye from UV
> damage;

Both of these points are correct. Although keep in
mind that I was merely indulging in a flight of fancy
as to the perfect designer eye I would like to have.
Reality didn't really enter into it. Keeping in mind
it is merely a pipedream, one could argue that the
polarizing lens of my hypothetical eye would prevent
glare and the transparent third eyelid could operate
as a UV shield that could be lowered when one actually
wanted to view things in that wavelength.

> and someone correct me if I'm wrong, but I
> believe hawks, while they
> have superb distance vision, can't focus sharply on
> nearby objects.
> There
> are always tradeoffs; neither evolution nor
> intelligent designers can
> provide all possible features in a single design.

Your overall point on tradeoffs are correct.
Constraints favor specialization over generalization.
Thus you can design a swiss army knife that is
incredibly versatile, but an axe is preferable for
cutting firewood and you are better off with a hunting
knife to skin game. 

As far as hawks go, however, your belief is false.
Hawks and other diurnal raptors have both excellent
distance vision and incredible accomodation. Their
lens can change shape much quicker than ours can to
track prey close up as well.

It takes but a moment's consideration to realize this
is true. What good is it to be able to see a mouse
from a mile away if when you come within striking
distance at high speed, you lose sight of it?

Hawk eyes are also unusual in that they have two high
resolution foveas (areas of retina densely packed with
photoreceptors) one in the center of the retina like
ours and another on the side which we do not have.
This means that a hawk's peripheral vision at certain
angles is as high resoultion as its direct gaze. Truly
beautiful and amazing. 

Hawk eyes do however have their tradeoffs as well.
They are incredibly large. If you look at a hawk's
small areodynamic skull, it is almost all eyesocket
leaving room for only a tiny brain.  
 
> As it stands, we are lucky if we have
> > 20/20 vision. I sure don't w/o corrective lenses.
> >
> 
> Me neither. Since there is substantial variance
> among humans in visual
> acuity, and I would have expected evolution to mop
> that up, here's a
> question to which I'd be interested in the answer if
> anyone knows it:
> 
> Do populations which followed a hunter/gatherer
> lifestyle until recently
> have the same variance in visual acuity as those
> which have been farming for
> a few thousand years?

I am unaware of any actual data on this subject but I
would be willing to bet that hunter gatherers have a
higher average visual acuity and smaller variance.
Just my gut feelings as a biologist. :)

Stuart LaForge
alt email: stuart"AT"ucla.edu

"God doesn't play dice with the universe." - Albert Einstein

"Einstein, don't tell God what to do." - Neils Bohr

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