Colourblind people: evolutionary advantage?

[jovan]

@engineer_comp_geek

Rods see black and white (they give you your detail vision) and see in low light conditions.

Nitpick: in the daytime, rods do not contribute significantly to vision, as the rods are completely inhibited by the brightness. (Somewhat un-intuitively, retinal receptors are inhibited by light, they fire less and less, the brighter the light.) Furthermore, more receptors does not necessarily translate to greater visual acuity. In the case of rods, the greater number of cells allows larger “sensor sizes”, with the output of several rods being summed before leaving the retina. Overall, rods have much lower spatial acuity than cones. Even with cones, the signal that goes out of the eye goes through spatial filters that involve several neighbouring cells.

@Colibri

As mentioned above, some primates, including Old World Monkeys, apes, and humans, and a few New World Monkeys, re-evolved a third color receptor. This is probably an adaptation for locating fruit, which was already brightly colored so birds could find it.

That’s the common view, but there is also a hypothesis, championed by Mark Changizi, that the purpose of the third cone is to allow primates to better read each others’ skin. The argument goes that dichromats that depend on fruit don’t have that much problem finding them so the evolutionary pressure isn’t huge there. Trichromat primates all have naked skin visible on their faces, whereas dichromats do not. The peak spectral sensitivity of the L (red) and M (green) cone perfectly match a spectral peak and trough of skin spectral reflectance that are due to oxygenated hemoglobin. In other words, primates who have L and M cones are able to tell the level of oxygenation of others’ capillaries. With a naked face, we’re able to tell when others blush, are angry, or sick. For social animals that need to intensively care for their newborns, this is a great advantage. That it also allows you to better judge the ripeness of fruit is a secondary advantage. Or so goes the argument. (Changizi has a bad tendency to overstate his case in his popular writing.)

[clairobscur]

@Colibri

It’s really impossible to understand how colors we can’t perceive might look to an animal which can see them. How would you describe the sensation of “red” to a color-blind person?
.

That wasn’t was I wanted to ask. Rather, I wanted to know if they could see two kinds of “red”, or rather two kinds of “blue”, or whether it depended on the specie, or maybe if it was something weirder than that.

But Broomstick’s mantis shrimp is weird enough. Not only is it dodecachromat (while I was making up this word fully expecting that no creature would be like that), not only have they eyes mounted on stalks that can move in any possible direction, not only do they see in the infrared and the ultraviolet, but they also see stuff I didn’t even know existed like “circular polarized light”. :eek:

[clairobscur]

@thelurkinghorror

Colibri covered it, but for example see spectral sensitivity curves. A new cone would work best if it is in a area of “low coverage,” e.g. ultraviolet to the left, between S/M in middle, or infrared to the right. Most suspected human tetrachromats would have a fourth cone close to the L, M, so no mindblowing changes.

.

Interesting. It seems that our “coverage” isn’t optimal at all, with two close peaks.

As for tetrachromat people I envisioned asking if there were any, then deleted the question thinking it would be too important a mutation to exist, or that if it had existed it would have been so incredibly rare in the history of mankind that it would have gone unoticed. Things are much weirder than I thought, both for animals and humans.

[RaftPeople]

@barbitu8

Some are born with better than 20/20. I knew someone who had 20/10. Many pilots have better than 20/20. I was told by an optometrist that the difference is in the number of cones. If this is not so, how do you explain vision better than 20/20?

Based on the link I posted above, it would seem (possibly) it relates more to the structure of the visual cortex.

[thelurkinghorror]

Broomstick: I don’t know where you got that I suggested color normals do not adapt to their environment. The point is: if you run tests on a person’s physiology and then make an assumption on what they see, you would be making an error. Anomalous trichromats have much better color vision then their physiology suggests, due to post-receptor factors. Their difficulties only show up in very specific situations. Thus, the only way to “prove” what someone sees is to test their behavior, not what pigments they have or neural connections.

and re: flight, I think there are different rules/criteria for exclusion between the FAA, military, European groups etc. Some people are in the odd position of being excluded from flying in one and allowed in another. The lease stringent test accepted by many has you discriminating between red, green, and white lights at various brightnesses. I am glad that it worked out for you, 99% of people with color deficiencies are likely at little risk while flying. It would be better if non-opposing colors were used on planes however.

@engineer_comp_geek

Cats, however, despite having some color receptors in their eyes, won’t choose food based on container color. For a very long time, researchers thought that cats were somehow deficient elsewhere, perhaps lacking something in their brain to process the color information from their eyes. It wasn’t until the 60s or 70s that someone was able to prove that cats are not in fact colorblind, and can be trained to select food based on container color. For some reason, though, training cats to do this is extremely difficult. And by extremely difficult we’re talking well over a thousand tries before they finally start to get it right. No wonder researchers used to believe they were colorblind. After trying it a few hundred times with complete failure you’d be tempted to write cats off as colorblind as well.

Terminology: in the scientific context, colorblind means “less color perception than humans.” In other words, dogs and cats are colorblind, as are all mammals besides apes, some monkeys and cetaceans and pinnipeds (those last two can’t normally see color at all). Despite being colorblind, cats and dogs can see many colors. Confusing yet?

@barbitu8

Some are born with better than 20/20. I knew someone who had 20/10. Many pilots have better than 20/20. I was told by an optometrist that the difference is in the number of cones. If this is not so, how do you explain vision better than 20/20?

A number of ways. But I wouldn’t jump to cone count as my first conclusion. See here, the cone matrix (coloration is artificial, they look identical under a microscope). There’s not much room to squeeze new cones in.

@clairobscur

Interesting. It seems that our “coverage” isn’t optimal at all, with two close peaks.

As for tetrachromat people I envisioned asking if there were any, then deleted the question thinking it would be too important a mutation to exist, or that if it had existed it would have been so incredibly rare in the history of mankind that it would have gone unoticed. Things are much weirder than I thought, both for animals and humans.

There are people (females) with 4 cone types, it is still being tested whether there are any actual behavioral differences. I’m not up to speed on the research here. And actually, the peaks I showed in that link are “ideal” numbers, there are tons of different expressions across humans, the main constant is that color normal people have three types, and the types (especially L & M) are sufficiently far apart.

By the way: really cool website. You can simulate the three types of colorblindness on an image from the internet or uploaded.

[Broomstick]

@clairobscur

As for tetrachromat people I envisioned asking if there were any, then deleted the question thinking it would be too important a mutation to exist, or that if it had existed it would have been so incredibly rare in the history of mankind that it would have gone unoticed. Things are much weirder than I thought, both for animals and humans.

Human tetrachromats probably do, in fact, exist (two cases are mentioned here). So far as I know, they’re invariably female. What happens is that a woman who is a carrier for certain forms of colorblindness, the “anamalous” trichromats, winds up with, say, two types of cone cells that respond to green (or red, or whatever the mutation is for). This should give them four different cone cells with different peak sensitivities. It does seem to improve their color discrimination, but there hasn’t been a lot of research done the topic. It might be 2-3% of women worldwide, but no one really knows for sure.

[Snnipe_70E]

@barbitu8

Some are born with better than 20/20. I knew someone who had 20/10. Many pilots have better than 20/20. I was told by an optometrist that the difference is in the number of cones. If this is not so, how do you explain vision better than 20/20?

I doubt that there are many color blind pilots. I would think that being color blind would disqualify them.

I had a few classmates at the Maritime Academy who applied for the deck division. During the physical their being colorblind was discovered. They were told they could not qualify as a Mate so they could not apply to the deck department, but if they changed major to engineering they would be admitted to the Academy.

[Broomstick]

@thelurkinghorror

and re: flight, I think there are different rules/criteria for exclusion between the FAA, military, European groups etc. Some people are in the odd position of being excluded from flying in one and allowed in another. The lease stringent test accepted by many has you discriminating between red, green, and white lights at various brightnesses. I am glad that it worked out for you, 99% of people with color deficiencies are likely at little risk while flying. It would be better if non-opposing colors were used on planes however.

The problem is that finding non-opposing colors that truly work for everyone is nearly impossible. Red/green are problematic, but there are people with other forms of non-normal color vision with different problem pairing, like blue/yellow.

The US’s FAA take the position that what really matters is can you tell the various signal lights apart in a reliable manner. If you can, it doesn’t matter if you can see the correct colors or not because you’ll still respond properly to the signal. Other nations just flat-out say unless your color vision is perfectly normal you can’t legally fly, regardless. This can also play out in driving laws - the US pretty much ignores whether someone is colorblind or not while driving, but some other nations (I think Hungry is one of them) just flat out forbid anyone with any form of colorblindness from driving a car.

In one case, the governing authority is saying “we only want normal people to do this” and in the other the authority is saying “if you can understand lights/colored signals and consistently respond in an appropriate manner you can drive regardless of what colors you actually see.” This can happen with one-eyed people as well - the US makes prospective one-eyed pilots take a specific test to demonstrate they can adequately compensate for the lack of stereoscopic vision and if so, they can fly without restrictions. Other countries just flat out say you need two functional eyes to be allowed to fly. While there is no disputing that the one-eyed lack stereoscopic depth perception, that’s not the only way the brain determines depth in what is seen and in fact out past about 50 feet binocular vision is not terribly useful for depth perception, your brain uses other cues. Again, most of the problem is that the mainstream overestimates the impact of the visual anomaly in regards to actual function. Sure, one-eyed vision does have drawbacks in very specific conditions, but those conditions seldom apply in the real world.

By the way: really cool website. You can simulate the three types of colorblindness on an image from the internet or uploaded.

I really wish someone would try to come up with an alogarithim to “color correct” for us anomalous trichomats - so much emphasis seems to be on the “opes” who completly lack a particular color perception, the anomalous seem to get lost.

[thelurkinghorror]

Thanks for the info. By non-opposing, I meant say putting signal lights in red and blue, then it is unlike that the colorblind pilot would confuse then.

Seems kinda annoying: games like Bioshock make an essential discrimination task rely on red vs. green, so truly colorblind gamers are screwed.

Opes are looked at because they are more extreme and “sexy.” Still, the anomalous should get more interest than they do. For example, deuteranomaly is IIRC ~8% of males. It’s pretty common, and it would be nice if there was more interest/recognition in both simulations and aviation and driving.

[RaftPeople]

@Snnipe_70E

I doubt that there are many color blind pilots. I would think that being color blind would disqualify them.

I know a former air force pilot that knew the color blindness would be tested for and he ordered all of the different color blindness tests (different mfg’s) and practiced by looking for any identifying characteristics, serial numbers, other patterns, etc. which allowed him to pass the tests.

[Broomstick]

@Snnipe_70E

I doubt that there are many color blind pilots. I would think that being color blind would disqualify them.

I don’t know about the military rules, but among civilian pilots in the US there are thousands of them, actually most likely in the five digits, because the US rules allow pilots with several types of colorblindness to fly. When I went to take my lightgun test the gent testing me said he’d had about 10 other women show up over his career for the same test, which given how small a percentage both women in aviation and colorblind people are is pretty interesting. He’d seen hundreds of male applicants for the test, most of whom apparently passed without much problem. The test is pretty straightforward, you can either do it or not.

Even the “opes” are allowed to fly in the US, they just aren’t allowed to fly at night or in situations where light signals are used. So they’re restricted, but not barred. I know there are some out there flying because I’ve met them.

If 8% of pilots in the US are colorblind that would be about 60,000 colorblind pilots. 8-9% is the rate in the general population, not sure if that would apply to US pilots or not.

[Broomstick]

@thelurkinghorror

Thanks for the info. By non-opposing, I meant say putting signal lights in red and blue, then it is unlike that the colorblind pilot would confuse then.

The thing is, they use three colors for light signals, so it’s not just pairing.

Currently, they use white/green/red. For deuteropes, that’s a problem because they wouldn’t be able to distinguish green from white. For the deuteranamalous, such as myself, the green is often seen as blue so, in essence, for me the triad actually is white/blue/red - which has occasionally caused a bit of confusion when I say “see the blu— er, green signal”

But if we went to officially red, blue and white the protanopes wouldn’t be able to distinguish the red from the white. I’m not sure what a protonamalous person would see - white/yellow/blue?

Seems kinda annoying: games like Bioshock make an essential discrimination task rely on red vs. green, so truly colorblind gamers are screwed.

It IS annoying. Even as an anamalous there are a couple places in World of Warcraft I have some trouble, although WoW is implemeting a “colorblind” mode not just for red/green problems but for something like 10 different forms for colorblindness, including monochromacy. I’ve seen some of the testing for it and it’s really helpful. That, and some of the color normals have mentioned using the modes for “mood lighting” as it were, or role playing Worgen (I guess since they’re “werewolves” some folks imagine they have the color vision of dogs rather than apes). There’s a bit on it here

With something like 10-11 million subscribers that works out to what, about 800,000 colorblind WoW players assuming the 8% rate applies? Yeah, probably worth the effort given that those subscriptions run to about $1,200,000 a month.

Other solutions involving labeling options for various features. But yeah, being colorblind in a gaming world can be annoying.

It’s pretty common, and it would be nice if there was more interest/recognition in both simulations and aviation and driving.

I’m pretty cool with how the FAA handles the issue - it comes down to whether or not there’s a safety issue. They don’t care how you distinguish the colors, just that you can do so. That seems the best way to handle it as far as I’m concerned, but maybe I’m biased, being dueteranamalous

[Hari_Seldon]

I wonder if I have some sort of color anomaly. What she sees as blue, I sometimes see as violet and what she sees as green, I sometimes see as blue. These are borderline distinctions, though. I have no problem with red/green though; they are entirely different.

I don’t understand why the authorities permit horizontal traffic lights. They must be very difficult for red/green dichromats. My father was one and was really disconcerted by the traffic lights in Atlantic City which saved money by having only three bulbs so that the E/W traffic lights had the usual red on top, green on the bottom, while the N/S ones were reversed.

[j666]

I’m still dealing with the fact that someone tried to train cats.

[barbitu8]

@j666

I’m still dealing with the fact that someone tried to train cats.

Yeah. Usually it’s the other way around.

[BigT]

@Broomstick

I really wish someone would try to come up with an alogarithim to “color correct” for us anomalous trichomats - so much emphasis seems to be on the “opes” who completly lack a particular color perception, the anomalous seem to get lost.

The emphasis is because, as you say above, you guys don’t have nearly as much trouble as one would expect distinguishing colors, and thus making sure colors are distinguishable to colorblind people is usually sufficient for it to be distinguishable for anomalous trichromats. An image modifier would be more for scientific curiosity than actual practical use. Not to mention it would have to be fine tuned for each person.

@Hari_Seldon

I wonder if I have some sort of color anomaly. What she sees as blue, I sometimes see as violet and what she sees as green, I sometimes see as blue. These are borderline distinctions, though. I have no problem with red/green though; they are entirely different.

Well, even normal trichromacy is not 100% exactly the same in every person. Both of the two color pairs you mention are often a bit off. It’s not really considered anomalous, though I guess it technically is.

I don’t understand why the authorities permit horizontal traffic lights. They must be very difficult for red/green dichromats. My father was one and was really disconcerted by the traffic lights in Atlantic City which saved money by having only three bulbs so that the E/W traffic lights had the usual red on top, green on the bottom, while the N/S ones were reversed.

Well, for one thing, lights in the U.S. are supposed to have a little yellow mixed into the red and blue mixed into the green. (I personally can see the latter really easily, but the former is a bit harder to see. Red-orange and red always have looked rather close to me.) But apparently the difference isn’t enough for many deuteranopes, either, which sucks.

[Broomstick]

@BigT

The emphasis is because, as you say above, you guys don’t have nearly as much trouble as one would expect distinguishing colors, and thus making sure colors are distinguishable to colorblind people is usually sufficient for it to be distinguishable for anomalous trichromats. An image modifier would be more for scientific curiosity than actual practical use.

Nothing wrong with scientific curiousity - but it WOULD demonstrate to the normal trichromats just how little problem being an anomalous is (in my opinion). It would break that idea that an anamalous trichromat somehow sees the world in monotone or is to be pitied or “fixed”.

Not to mention it would have to be fine tuned for each person.

Why? Anamalous trichromats are shifted a fairly consistent amount, it’s not a unique mutations for each instance.

[2gigch1]

@Hagen

So is there an advantage to being Colourblind?

Yes. It got me out of a LOT of grade school coloring assignments.

Interestingly I am a videographer by trade today, where color knowledge is important. I work around it.

[Ludovic]

@j666

I’m still dealing with the fact that someone tried to train cats.

@barbitu8

Yeah. Usually it’s the other way around.

In Russia, Rasputin trains YOU! There is a cat that really was gone.

[Una_Persson]

@Hagen

I was reading up the article about traffic lights and Colourblind people when I recalled a story relayed to me by a friend. Yep a bad start already, I know. It was told to him by an ex-SADF soldier during the border war who said that he had been a spotter in helicopter patrols because, being Colourblind, he could pick out camouflage from background foliage more easily.

I’ve heard that traffic lights’ red and greens are designed to be different shades so that you can tell them apart (not that I noticed) and vaguely remember reading from an online source about a study linking colour blind animals to some selective pressure.

So is there an advantage to being Colourblind? If so it a learned skill to help one function in a three tone world,or is it intrinsic to the biology? Or is it just more lies and Internet rumours?

Kind regards
Luke

Luke

You will be pleased to know that your question was forwarded on to Cecil by myself, and he chose to run with it in today’s newspaper column. You can find it here:

The Straight Dope: Is colorblindness an evolutionary advantage?

Una Persson
For The Straight Dope