Advantages of vision defects?

February 9, 2009 5:34 PM

Evolutionary advantages of far-sightedness and partial color blindness?

I've read that partial color blindness can improve night vision and the ability to spot certain forms of camouflage, however I haven't been able to find much about the mechanism behind this. I'm looking for anecdotes or articles about this, or about any other advantages that color blindness or far-sightedness might confer (if any), either from an evolutionary standpoint, or in modern life.

posted by paradoxflow to science & nature (16 comments total)

I can't imagine that this would be advantageous in any way, but then I think about stuff like periphery vision and realise I really haven't got much of a clue about anything.

So:

Talk Origins on the Evolution of Vision

Anecdote 1, Anecdote 2, Discover article
posted by turgid dahlia at 5:43 PM on February 9

No snark, but if you Google "color blindness camouflage" you'll find a bit of stuff.
posted by turgid dahlia at 5:45 PM on February 9

It is a common mistake to suppose that apparently maladaptive traits provided some sort of selective advantage at a past point in evolutionary history. This is not necessarily the case. While anecdotes and just-so stories can fit this mistaken preconception, they usually provide only poor evidence for it.

I am not saying that you hold this mistaken preconception, or that these traits did not provide some sort of advantage (turgid dahlia provides some good evidence that suggests that they did), but that one should be cautious about taking it as a premise.
posted by grouse at 5:56 PM on February 9 [2 favorites]

Most likely there is no evolutionary advantage - although I'm no expert on evolutionary biology my guess is there's just not enough of a disadvantage for it to have been selectively bred out.
posted by fearnothing at 6:02 PM on February 9 [1 favorite]

My vision defects gave me some excellent nerd cool from my NHS specs.

Seriously, not everything confers an evolutionary advantage. I kind of like being an evolutionary cul-de-sac.
posted by arcticseal at 6:12 PM on February 9

I wasn't making any assumptions about there necessarily being any advantages to those defects (especially far-sightedness), but since I was surprised to hear about the night vision/camouflage perception advantage, the main question was whether or not there were any other such advantages I hadn't heard about.

Thanks for the answers so far.
posted by paradoxflow at 6:30 PM on February 9

the main question was whether or not there were any other such advantages I hadn't heard about

Well, I don't know how much currency this argument has among the evo pros since I've read very little literature, but it's my opinion that our bodies falling apart after age 40, when our progeny are fully independent, is an evolutionary advantage for them and thus for our shared genes. This is prolly echoing something in The Selfish Gene I would think.
posted by troy at 6:44 PM on February 9

There are two types of visual receptors in your eyes - rods and cones. One type is colour sensitive, the other is not but is far more sensitive to intensity and change. So presumably the mechanism is that in some cases of colour blindness, either there are more rods than cones active in the retina, or the person is more dependant on their rods than usual.
Other advantages to seeing with more rods than cones would presumably be being more able to notice small/quick movements.

As for advantages of colour blindless that you haven't heard of, perhaps Human tetrachomacy - where the right combination of colour-blind genes can theoretically produce a female able to see colour with greater acuity than normal people. (This is why your mom tells you your clothes don't match, and for the life of you, you can't figure out why not :-)
posted by -harlequin- at 7:18 PM on February 9

With my farsightedness, I can see what bus is the one arriving at the bus stop way before anyone else can.

May seem minor, but the nearsighted at the stop are grateful when I can tell them what route it is.
posted by spinifex23 at 11:28 PM on February 9

Well, the theory goes that certain types of color blindness can see through camouflage, right? So, that would be helpful for picking out berries.

Just on a whim, think of what that would mean for your ability to distinguish various forms of tartan. Ponder that for a second, the conditions under which tartan was worn and might be important in the life-or-death sense, then go look up the incidence of color blindness in the Scottish. Hrm.
posted by adipocere at 12:12 AM on February 10

You definitely want to be careful when discussing the evolutionary advantages of colour blindness (or other vision defects), for the reasons outlined by grouse and fearnothing above.

I would like to add that some people believe that protanopia (red-green colourblindness) is, in fact, an indication that the blue cone was evolved first, then followed by the red and green -- that we, as a species, have not completely evolved the distinction between red and green. Indeed, the photoreceptors for red and green are extremely similar in both their responsivity spectra: whereas the blue cone (labelled here as S, for its sensitivity to light of short wavelength) is off to the left of the graph, the green and the red (M and L for medium and long wavelengths, respectively) overlap greatly. In this sense, red-green colourblindness is not really a defect, but rather a remnant from our earlier evolutionary history. According to this interpretation, it becomes hard to talk about potential advantages of being colourblind.

In general, any discussion of advantages and disadvantages in a specific trait will be highly context-dependent. Farsightedness is, as spinifex23 mentions above, useful when reading faraway signs; it is not so useful when reading a book up close. So, maybe it is more helpful to ask for specific circumstances when non-normal vision can be useful, rather than asking for a general evolutionary advantage.

Anecdotally, I know at least one protanope (red-green colourblind person) who claims that he can perceive some ultraviolet light, although I don't know if his UV sensitivity is directly caused by his colourblindness. My pet theory is that, like with bees, some protanopes' primary colours are UV, blue, and green. This is probably completely and utterly wrong since -- as far as I know -- there is no biochemical reason why this should be. It's still pretty fun to think about, though. As for advantages, I can't think of any specific situations that are not horribly contrived -- e.g., the world is about to end and the only anti-armageddon button is labelled in UV.

Speaking of UV, people without lenses (e.g., due to cataract surgery, etc.) can report UV sensitivity. Normally, the lens blocks out some UV rays, presumably to protect the retina from the energy-intense waves. Obviously, removing the lens exposes the retina to UV light, which means that the photoreceptors can react to the presence of UV.
posted by tickingclock at 1:08 AM on February 10 [1 favorite]

I'm not colorblind, but I think I can see some ultraviolet. Some purple flowers seem dark in terms of color but bright in terms of my eye's reaction to them. I theorise that they're reflecting lots of ultraviolet and that I'm picking this up somehow - perhaps through the rods in my eye?
posted by Joe in Australia at 2:24 AM on February 10 [1 favorite]

Joe in Australia, there are receptors more sensitive to blue light in the ganglionic layer of the retina which is in front of the layer containing the rods and cones; these allow some blind people who lack functional rods and cones to synchronize their circadian rhythms by light exposure:

It turns out that mammals have an additional light-sensitive photoreceptor in the retinal ganglion cell layer (pRGCs) that is directly sensitive to light and is primarily responsible for mediating these responses. These cells are most sensitive to short-wavelength light with a peak sensitivity at ~480 nm, in the visible blue light range. While these studies and others in sighted subjects suggested that this non-rod, non-cone photoreceptor might play an important role in human photoreception, this had yet to demonstrated unequivocally until now.

I would guess the extra level of response you experience from looking at these purple flowers stems from the fact they are stimulating to the ganglionic layer receptors.

Oliver Sacks discusses (sorry about the pay wall; I think the same essay is collected in An Anthropologist on Mars) the case of an artist who lost all color vision as a result of a brain injury from a car accident, and who claims to have gained the ability to see as much texture and detail in dim moonlight as normals can in the brightest sunlight.
posted by jamjam at 9:25 AM on February 10

I'm not colorblind, but I think I can see some ultraviolet. Some purple flowers seem dark in terms of color but bright in terms of my eye's reaction to them. I theorise that they're reflecting lots of ultraviolet and that I'm picking this up somehow - perhaps through the rods in my eye?

Does this happen to you all the time, or only at dusk? If the latter, you might be experiencing the Purkinje effect, which is caused, in fact, caused by the different sensitivities of rods and cones.

Under low light conditions, such as at dusk, rods are activated but cones are not. Because rods also respond to higher frequency spectra (i.e., blue and violet), this means that you become more sensitive to bluish colours -- i.e., experience them to be brighter -- in dim light than in daylight. As a result, purple flowers seem brighter.

On the other hand, if you see the UV all the time, then maybe what jamjam is discussing is more likely. Which, BTW, is a very cool finding!
posted by tickingclock at 11:17 AM on February 10

As I recall, this visual effect happens only in bright daylight. It's hard to be definitive about something so subjective but I don't get any impression of shape; it's just that the flower "looks brighter" than it should. When I look at something white in full sun I get an impression of whiteness, but also glare - it's too bright to look at comfortably. The same thing happens with some flowers in full sunlight: they don't look bright but my eyes feel as if they're being exposed to too much light. They're dark in colour but bright in luminosity.
posted by Joe in Australia at 3:02 AM on February 11 [1 favorite]

They're dark in colour but bright in luminosity.

Yeah, that sounds like extra sensitivity to the high-frequency end of the visible spectrum, possibly bordering on the UV range. Cool stuff!
posted by tickingclock at 1:22 AM on February 14