Re: Why did color vision evolve?
- From: drosen0000@xxxxxxxxx
- Date: Wed, 14 Feb 2007 13:49:10 -0500 (EST)
On Feb 13, 11:43 am, "KoosHopeloos" <kooshopel...@xxxxxxxxxxx> wrote:
L.S.,Probably it evolved separately in different lineages for
Perhaps a very simple question, but why did (color) vision evolve?
different reasons. However, I conjecture that the big breakthrough in
color came when the flowering plants first evolved. The flowering
plants evolved colored pigments, in parallel to insects that developed
the color vision. Most flowering plants use insects to carry their
pollen to the ova where the seeds are pollinated. The first flowering
plants probably used scents to attract insects for this purpose. Smell
evolved among animals evolved much earlier, to find food. However,
plants evolved colored pigments to further entice the insects and
insects probably evolved color vision to find the flowers. The feed
back loop resulted in highly colored flowers and highly developed
color vision among insects.
The birds probably followed once the flowers and insects had
developed their symbiotic relationship. Once the flowers had color
pigments, the fruit developed by the flowers probably tended to retain
some of the same colored pigments. Then, some birds evolved the
ability to see colored pigments in order to find and eat the fruit.
Birds that eat fruit sometimes end up carrying the seeds long
distances, on their feathers or in their intestines. So some plants
with slightly colored fruit developed even stronger colors to attract
the birds. This probably started still another feedback loop where
fruit became colored and birds developed feedback loops.
Of course, some fruit eating monkeys eventually evolved colored
vision to take find the colored fruit. And here we are, eating fruit,
birds, and honey.
Probably not as much investment as you think. At least not
Much is known and speculated on how from a rudimentary eye, vision and
color vision might have evolved, but it seems like a big energy
investment. Also the brain would have to adapt or be able to
interpreted the signals.
starting from an animal that already has an image processing visual
system. Any eye that uses an imaging system has to use an array of
specialized cells to sense light from pieces of the image. The nervous
system of such an animal would have to already have evolved to process
the image coming from that array. All that is necessary for color
vision is that some of the cells have a different spectral sensitivity
curve than other cells in the array. That would initially come about
due to minute differences in chemical environment.
As an example, the cone cells in human being (a fruit eating
monkey that has recently diversified its diet) have different spectral
sensitivity curves. However, the chemistry of these cones cells is
almost identical. The difference in spectral sensitivity is caused by
slight differences in pH. There is no difference in the pigment
molecule that absorbs the light (rhodopsin) or even in the protein
that embeds the rhodopsin. However, a difference in pH shifts the
absorption curve of the rhodopsin by a very small amount.
Another question would be how the flowering plants evolved
pigments. I may have started with plants that had a variety of
scenting compounds (for attracting and repelling insects). Differences
in the molecules would cause differences in absorption spectra (i.e.,
color).
Not for finding fruit.
But still, why did (color) vision evolve? Wouldn't it be enough to see
in black and white?
....references?I currently have no references on the evolution of color vision.
However, for a general description of the physiology of vision I
recommend two books.
1) Brian A. Wandell, "Foundations of Vision" (Sinauer, 1995). ISBN
0-87893-853-2
Color vision Chapter 9, pp 287-340.
2) David Regan, "Human Perception of Objects," (Sinauer, 2000) ISBN
0-87893-753-6.
Color vision Chapter 3 pp 207-266.
Yes, there are uses for "half-color vision."
.
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