[extropy-chat] Looking for examples of naturally evolved X-ray vision?
pharos at gmail.com
Tue Jan 17 21:15:26 UTC 2006
On 1/17/06, kevinfreels.com wrote:
> I was helping my daughter come up with some ideas for a school science
> project and I stumbled onto a couple unknowns.
> Animals have evolved a wide variety of abilities to seek food and avoid
> predators. Echo-location, color vision, and compound eyes are just a few.
> All provide important information regarding the immediate surroundings. My
> daughter asked me why the visible light spectrum IS the visible light
> spectrum. After all, animals hear at a wide range of frequencies that humans
> cannot, so why not have the same thing occurring in vision? Are there
> animals with X-ray vision?
You need to read up on 'Evolution of Eyes'. Try:
Read a few more as well, to get other opinions.
Basically, he says:
Why Do We See What We See?
All eyes are sensitive to a common, rather narrow range of wavelengths
within the broad spectrum of energy produced by the sun. Why is this?
Why can't we see more of this spectrum? The most likely explanation is
that eyes first evolved in animals living in water, and, water, due to
its fundamental nature, filters out all but two quite narrow ranges of
electromagnetic (EM) radiation.
As shown in figure 1, the range of EM radiation 'visible' for most
organisms is a narrow, sharply defined band, ranging from the very
short wavelengths we think of as having a blue color to longer
wavelengths we identify as red. It is particularly narrow when
compared with the full range of EM radiation produced by the sun. In
our language, we divide this narrow range of perceived wavelengths
into seven names (red, orange, yellow, green, blue, indigo, violet),
also called spectral colors. As is clear from the figure, in this very
narrow band, EM radiation penetrates water better than the adjacent
wavelengths by about 6 orders of magnitude. So, since our ultimate
ancestors existed in a watery slime, the only radiation to penetrate
water must have been the primary selective force. As we see now, this
early selection for the narrow spectrum ultimately drove the evolution
of biochemical mechanisms sensitive to these colors of light. This is
true both for perception of light by animals and for photosynthesis by
plants. Now, five billion years later, though many animal species have
moved onto land where the sun's full spectrum is available, eyes
remain sensitive only to this narrow region. That limit comes now, not
from the filtering properties of water but rather from the biochemical
mechanisms that evolved in response to the limited wavelengths
penetrating the original slime.
*Once selection started organisms down that path, mechanisms that
evolved limited future options.* *(My emphasis)*
It is true that many insect species as well as some species of fish
and birds can 'see' in the ultraviolet, or very short wavelength end
of the visible spectrum. However, they do so with slight modifications
of the same biochemical system that the rest of us use to see, not
with new mechanisms.
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