From: Glenn Morton (glennmorton@entouch.net)
Date: Fri Jul 18 2003 - 17:22:20 EDT
Hi Walter,
You wrote:
>-----Original Message-----
>From: Walter Hicks [mailto:wallyshoes@mindspring.com]
>Sent: Friday, July 18, 2003 3:18 PM
>Sounds good but how does it explain why so many species got sight
>at more or less the
>same time? Sight would be great of course but why not just in a
>dominant species
>instead of the entire life system at that time. Is this question
>approached at all?
I did address it in the note, but only tangentially. The fact that
light-sensitive spots were found on precambrian animals gives some ability
of the animals to observe shadows. Light-sensitive spots are quite common,
being on leeches worms, jellyfish and bacteria. Animals like these, which
took evasive action when things darkened, probably had a slightly higher
chance of survival. That then allowed those who had mutations which allowed
better seeing (moving towards image formation) to have even a better chance
of survival. Now, if you evove a regionn of light-sensitive cells in a cup
shape, it can actually tell the direction of light (and laternatively the
direction of shadow. That is one simple step up from a mere light-sensitive
spot. It is also a step towards an image-forming eye which has a higher
survival value than merely a light spot. If the cup then becomes deeper,
all it takes is a cover with a pinhole to make an image-forming
pinhole-camera-style eye. After that, a lens is all that is left. This will
not take tens of millions of years given the selection pressure at the time.
That is why other animals also evolved eyes after the first predator was
loose. They either did or they died. (See Dissembling Dawkins, Climing Mount
Improbable, pp 138-197
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