Color Blindness Is Evidence of Evolution

Started by stromboli, April 25, 2014, 10:35:14 PM

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stromboli

http://www.skepticink.com/smilodonsretreat/2014/04/24/color-blindness-and-how-easy-evolution-really-is/?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+SkepticInk+%28Skeptic+Ink+%29

......"One new thing I learned was particular interesting given my interest in the creationist movements. One often hears about how difficult it is for complex things to evolve. Take vision for example. The eye is really complex and all the parts have to work together or there’s no vision. Well, that’s true… now. But it hasn’t been true throughout the history of life. The eye has evolved to be more complex as those animals with really good vision were simply better at surviving. But a scientist named Jay Neitz (featured in the third episode of Your Inner Fish) and several other scientists reported on just how easy it is to change the vision systems in the eye. The paper was in 2009 in Nature. [1] PDF First we need to talk about how color vision works. Humans have three types of cone cells in the eye. These are designated S, M, and L by the types of EM radiation that those cones respond to. Remember the phrase ROY G. BIV? That’s the visible light spectrum (a rainbow). Red is the longest wavelength, while violet is the shortest wavelength.  S-cones is our eye respond best to short waevlengths, the violet and blues, and very weakly to the other colors. The M-cones respond strongly to yellows and greens, but weakly to blues and reds. While the L-cones respond strongly to reds and oranges and weakly to blues. The combination of how these cones react give us a full spectrum of color vision. Well, most of us. Some people have a mutation in one of the genes (there are several) that controls the light sensitive pigments in our eyes, called opsins. The genes for these opsins are on the X chromosome.[2] This is why there are more males with color-blindness than females.  Females have two X chromosomes, so they have a ‘backup’ copy of the gene if one is damaged. This also explains the concept of tetrachromacy, which MAY mean that some women have four different cones instead of the usual three. Perhaps, they can actually differentiate more colors than us plain old trichromacy people. What I learned from Your Inner Fish was that the blue/green opsin in the L/M-cones seems to be a relatively recent innovation in evolution. They are really close together on the X_chromosome and they are really very similar. It’s almost as though the gene segemnt was duplicated, then one gene mutated and now responds to a different part of the spectrum than the other. That’s one hypothesis. Dr. Neitz was wondering if it’s really that simple. Could such a single change, a few mutations in a gene, really allow an animal to see more colors? Or would the brain simply not be prepared for it. In squirrel monkeys (Saimiri sciureus), some females have trichromatic vision, but all males are red-green color blind. The authors trained some male monkeys (I hate that term) to identify the part of a touch screen that had different colors.  If they got the selection correct, they got a treat.

These tests are exactly like the color-blindness tests that you get at the optometrist’s office.  Except the monkey’s got a reward for getting it right. After testing for more than a year, two males were injected with a virus that had been modified for a gene therapy role. The recombinant virus contain a human L-opsin gene with an L/M opsin enhancer and promoter. And yes, the three injections of viral particles was just underneath the retina. Shudder. If the opsins were all that were needed to see three colors, then the monkeys would be able to see colors that they hadn’t seen before. But if some rewiring of the brain was required, then the monkeys still wouldn’t see red/green even with the gene producing the L-opsin. A brief aside here. This is also a test of creationist claims. If things like color vision are as complex as creationists think, then just a simple change like this shouldn’t change anything in the monkeys. But if we do see a change in the monkeys ability to see colors, then the creationist claim is wrong. Simple changes to genes can produce very dramatic changes. Twenty weeks after the injections, the two males were no longer color blind. They could register all color differences. In fact, if I’m reading this paper correctly, it appears that the human L-opsin is superior to the squirrel monkey L-opsin because the males could actually see colors more effectively than the females. So, we see that the monkey brain can handle the additional inputs in an entirely different color spectrum. And it can readily use that additional information in a direct (profitable) way. And all that is required is a gene. This supports the claim that gene duplication followed by mutation is a method by which new abilities can be generated in populations of organisms. The other exciting thing is that this procedure may provide a way to restore full color vision to humans with certain types of color-blindness.

[/b]

More links
http://www.straightdope.com/columns/read/3037/is-colorblindness-an-evolutionary-advantage
http://http-server.carleton.ca/~btansley/psyc3702/notes/Evolution%20of%20colour%20vision.pdf

I love me some science.  :biggrin:

PickelledEggs

That's pretty neat. So I guess I have old vision genes, since I'm colorblind.

stromboli

Quote from: PickelledEggs on April 26, 2014, 08:47:06 PM
That's pretty neat. So I guess I have old vision genes, since I'm colorblind.

You would make a great hunter. During WW1 and WW2, color blind guys were picked for snipers becasue they aren't fooled by camouflage. Color blindness actually was a selected trait for that reason, back in the hunter/gather days. Successful hunters got the women, and passed on the genes.

You probably never thought about it, but if you go into Walmart, even today if you compare the colorfulness of women's clothing versus men's, you'll see men still tend to select drab or darker colors like tan, knaki and grays over bright colors. Women needed to be able to select by color, telling ripe from not ripe or over ripe, gathering fruits and vegetables.

PickelledEggs

So does that mean that colorblindness is an advantage? As in it evolved after regular color vision?

Sent via your mom


Poison Tree

Quote from: PickelledEggs on April 26, 2014, 11:16:55 PM
So does that mean that colorblindness is an advantage?
That would obviously depend on the situation. I think the color blind would be at a disadvantage finding ripe fruit/berries. On the other hand, it is my understanding that they can often spot/see through military camouflage and this *may* also mean that they could spot naturally camouflaged animals easier. I've even seem some random people on the internet go so far as to speculate (without any evidence as far a I could tell) that color blindness--which occurs in females much less frequently due to their two X chromosomes-- is (one of) the reason(s) men were hunters and women were gatherers in "primitive" society--if you put any stock into internet speculation
"Observe that noses were made to wear spectacles; and so we have spectacles. Legs were visibly instituted to be breeched, and we have breeches" Voltaire�s Candide

PickelledEggs

Really interesting. I guess based on what your role was to your tribe, way back when, certain traits flourished more than others.

Sent via your mom

stromboli

http://www.straightdope.com/columns/read/3037/is-colorblindness-an-evolutionary-advantage

Dear Cecil:

I heard about a soldier who had been a spotter in helicopter patrols because, being colorblind, he could pick out camouflage from background foliage more easily. I vaguely remember reading about a study linking colorblindness in animals to selective pressure. Is there an evolutionary advantage to being colorblind?

â€" Luke, via the Straight Dope Message Board

Cecil replies:

This may seem counterintuitive, but the answer sometimes is yes.

Let’s put this squarely. The case can be made that acute color vision is a primitive trait that tends to disappear as organisms and societies become more advanced. In fact, we’ve already lost acute color vision once in our evolutionary history, then got a version of it back later. If you’re the feisty type, you can argue that color vision is an obstacle to progress, and that in the perfect world of the future, we’ll see everything in black and white.

OK, I’m exaggerating, but you can’t dismiss the idea out of hand. Let’s start with the claim that colorblind soldiers are better at seeing through camouflage. This notion has been kicking around in military and scientific circles since at least 1940, but despite the obvious usefulness of such an ability, for a long time no one bothered doing any formal investigation other than one unpublished military study indicating there was nothing to it.

More recent research, however, suggests maybe there is.

In a study published in 1992, scientists flashed a pattern on a video monitor: a 30-by-30 grid of small rectangles, all of them oriented vertically except within a randomly located 7-by-7 "target area" where the rectangles were horizontal. Test participants were asked to press one of four buttons to indicate what quadrant of the screen the target area had appeared in. Some test participants had normal color vision, while others, so-called dichromats (I’ll explain below), had severe colorblindness rendering them incapable of distinguishing red from green.

In the first trial, all the rectangles were the same color, and participants in both groups had little difficulty spotting the target. In the next trial, the rectangles were randomly colored red or green. This time around, those with normal color vision did poorly â€" all they saw in the brief time the pattern appeared (a fifth of a second) was a jumble of red and green.

The dichromats, on the other hand, kicked butt. Without color to distract them, they spotted the target as easily as with a monochrome pattern. The same held true when each target rectangle was replaced with a capital A while the background rectangles were replaced with Bs. Despite this conspicuous difference, randomly coloring the letters red or green completely flummoxed those with normal color vision. The dichromats, on the other hand, were unperturbed, picking out the target as effortlessly as before.


http://discovermagazine.com/2007/apr/the-upside-of-color-blindness

Color blindness is not always a disadvantage, according toUniversity of Calgary primatologist Amanda Melin and her colleagues,who found that wild color-blind capuchins in Costa Rica are better atdetecting camouflaged insects than individuals with broader colorvision.

To determine how color vision affects insect hunting, theresearchers used DNA samples to distinguish capuchins that werepartially color-blind from those with a wider spectrum of color vision.Observations of capuchins foraging for surface-dwelling insects showed that color-blind capuchins made nearly 20 insect-capture attempts perhour, compared with only about 16 for those with normal color vision.

PickelledEggs

So basically I'm higher up in the stages of evolution  :fU: :super:

Poison Tree

It would seem that color blindness would be a disadvantage for driving, although I don't know how much of a selective pressure that would be (if I had to guess I'd say minimal). Normally for stop lights a color blind person could just think "stop on top, slow in the middle, go on the bottom" but driving at night, especially in snow or rain, may result in the driver being unable to tell if the light is top, middle or bottom. Then there are places, like Nebraska, that have stop lights sideways and an out of state color blind driver may not know if left or right is stop. Even worse, an older (distant) relative of mine grew up in a small town where, to save money, the stoplight was built to use only 3 bulbs to light all 4 direction--east/west colors were (top to bottom) red, yellow, green and north/south were green, yellow, red so when the top light was on east/west was told to stop and north/south to go.
"Observe that noses were made to wear spectacles; and so we have spectacles. Legs were visibly instituted to be breeched, and we have breeches" Voltaire�s Candide

PickelledEggs

Quote from: Poison Tree on April 27, 2014, 01:22:22 AM
It would seem that color blindness would be a disadvantage for driving, although I don't know how much of a selective pressure that would be (if I had to guess I'd say minimal). Normally for stop lights a color blind person could just think "stop on top, slow in the middle, go on the bottom" but driving at night, especially in snow or rain, may result in the driver being unable to tell if the light is top, middle or bottom. Then there are places, like Nebraska, that have stop lights sideways and an out of state color blind driver may not know if left or right is stop. Even worse, an older (distant) relative of mine grew up in a small town where, to save money, the stoplight was built to use only 3 bulbs to light all 4 direction--east/west colors were (top to bottom) red, yellow, green and north/south were green, yellow, red so when the top light was on east/west was told to stop and north/south to go.
I can identify red and yellow lights without a problem. It's the green ones that give me trouble. They're too bright and close to white for me to tell the difference. If I'm at an intersection that I'm unfamiliar with (and there are no cars around to serve as some reference), I don't even know there is one there when it's green.

Essentially harmless so far as I can tell.

stromboli

I believe color blindness most commonly runs in the blue-green region, for some reason. I happen to have a slight dficiency in that area myself.