Why can't we see infrared?

[Diagoras]

Why did humans not evolve the capacity to see infrared light? Are there animals that can? It seems like it would be a great evolutionary advantage to see a predator's body heat in the dead of night. Could it just be a mutation that never occurred? Is there some sort of physical limitation on the wavelengths our eyes could perceive? Is it not as beneficial as my intuition says it should be?

[godless dave]

Originally Posted by Diagoras

Why did humans not evolve the capacity to see infrared light? ... It seems like it would be a great evolutionary advantage to see a predator's body heat in the dead of night. Could it just be a mutation that never occurred?

I can't answer all your questions, but I will answer the last one. Yes. Just because a trait would be beneficial doesn't make it inevitable that it will appear.

[Professor Yaffle]

Quote:

Some animals can see well into the infrared and/or ultraviolet compared to humans, enough to help them see in conditions humans cannot.

http://en.wikipedia.org/wiki/Night_vision

Quote:

Rattlesnakes and other pit vipers use their eyes to see during the day. But at night they use infrared sensory organs to detect and hunt warm-blooded prey. These infrared "eyes" are cuplike structures that form crude images as infrared radiation hits a heat sensitive retina.

http://animals.about.com/cs/zoology/a/aa061801a.htm

I presume that fact that humans are not nocturnal might have something to do with it.

[Lensman]

Have you ever seen an infrared image?

It's badly lacking in detail, infrared would only be useful at night & we evolved to be dormant at night-time.

[Bikewer]

There are creatures that can sense infrared, notably pit vipers. They don't actually "see" in this range, they sense body heat via the "pits" that lie between eye and nostril.

I don't know of any mammals offhand that have this ability; maybe it's just a variation that's not in the mammalian DNA set.

[JoeEllison]

Well... it wouldn't be very useful compared to how much of a disadvantage it would be. Infrared vision in humans wouldn't be like switching night vision goggles on and off, it would be more information on top of the information we get from the visible light spectrum. Now, imagine seeing heat in the daytime near the equator, the infrared waves reflecting off of every object blurring everything into a nondescript nothing.

[godless dave]

Lots of insects can detect light in the ultraviolet wavelength with their eyes. I don't know nearly enough about biology to know if it would work at the other end, and if not, why not.

[Professor Yaffle]

Originally Posted by Bikewer

I don't know of any mammals offhand that have this ability; maybe it's just a variation that's not in the mammalian DNA set.

Possibly ferrets?

http://adt.waikato.ac.nz/uploads/app...ic/01front.pdf

[Madalch]

Having a wider range of colour vision would not be particularly advantageous, since the refractive index of a material (such as the lens, cornea, and vitreous humour of our eyes) will depend on the wavelength of light passing through it. That's why blue text on a red background looks like it's vibrating- your eye cannot simultaneously focus on both the red and the blue. If your eye tried to focus on ultraviolet as well, it would be even less focussed.

I read (in either Asimov or Clarke) that the first artificial corneas were transparent to ultraviolet, thus allowing the wearers to see a far greater range of blue and purple than normal. But the newer ones are UV-opaque, so that it's easier to focus sharply on whatever it is one is looking at.

[Paulhoff]

Originally Posted by Madalch

Having a wider range of colour vision would not be particularly advantageous, since the refractive index of a material (such as the lens, cornea, and vitreous humour of our eyes) will depend on the wavelength of light passing through it. That's why blue text on a red background looks like it's vibrating- your eye cannot simultaneously focus on both the red and the blue. If your eye tried to focus on ultraviolet as well, it would be even less focussed.

I read (in either Asimov or Clarke) that the first artificial corneas were transparent to ultraviolet, thus allowing the wearers to see a far greater range of blue and purple than normal. But the newer ones are UV-opaque, so that it's easier to focus sharply on whatever it is one is looking at.

I thought that was lens, but you could be right.

Paul

[Olowkow]

Really interesting question and good responses. I have a good friend who is has done research for many years on eyes of all kinds of animals, in vivo and otherwise. Just fascinating stuff. I will email him and post the response.

[Madalch]

Originally Posted by Paulhoff

I thought that was lens, but you could be right.

I could also be wrong- it's been a long time since I read that article. I'm fairly sure it wasn't the retina, at least.

[CapelDodger]

Originally Posted by Diagoras

Why did humans not evolve the capacity to see
infrared light?

Because we're mammals. Acute hearing is the mammalian USP. We don't need no freakin' infrared. Leave that to snakes and the like.

[Paulhoff]

Originally Posted by Madalch

I could also be wrong- it's been a long time since I read that article. I'm fairly sure it wasn't the retina, at least.

You can't replace the retina, a many a blind peoson will tell you that.

Paul

[BenBurch]

Now, yes, you can replace a retina. But that is very, very recent, and highly experimental and does not work as well as the real thing.

http://artificialretina.energy.gov/

[CapelDodger]

Originally Posted by Professor Yaffle

Possibly ferrets?

http://adt.waikato.ac.nz/uploads/app...ic/01front.pdf

It's late on a Friday night so I don't know quite what to make of that. Brilliant parody, or deeply sad in a whole new way? If I were a Kiwi it would probably be easier.

Quote:

"... their status as potential vectors of Bovine Tuberculosis. There was suspicion that ferrets could detect the infrared light-emitting equipment used ...

Show me a farmer that isn't unshakably suspicious of the wildlife on his patch.

[Paulhoff]

Originally Posted by BenBurch

Now, yes, you can replace a retina. But that is very, very recent, and highly experimental and does not work as well as the real thing.

http://artificialretina.energy.gov/

That is not a retina replacement by a long way.

Paul

[Ron_Tomkins]

Originally Posted by Diagoras

Why did humans not evolve the capacity to see infrared light?

We're already pretty destructive predators. We don't need to go all the way.

[geni]

The thing you have to remember is that the mechanism for seeing is going to be pretty vulnerable to mutations (think the various forms of colour blindness). This means that there has to be a fairly strong selective pressure to keep it intact. Now in the case of basic vision and colour vision there is such a selective pressure (no sight is a major disadvantage colour-blindness less so but still enough to be selected against). There may not be enough selective pressure for UV and IR vision to be formed let alone kept.

[plumjam]

Originally Posted by Ron_Tomkins

We're already pretty destructive predators. We don't need to go all the way.

http://i127.photobucket.com/albums/p...dator1Head.jpg

You've got to feel for Gene Simmons. He isn't aging at all well.

[Ron_Tomkins]

Originally Posted by plumjam

You've got to feel for Gene Simmons...

I'll pass.

[plumjam]

Originally Posted by Ron_Tomkins

I'll pass.

Given that we don't have infra-red vision, about half the time there's just no option but to have to feel for him.

[BenBurch]

Originally Posted by Paulhoff

That is not a retina replacement by a long way.

Paul

Sure beats total blindness...

[Jeff Corey]

Originally Posted by Madalch

... That's why blue text on a red background looks like it's vibrating- your eye cannot simultaneously focus on both the red and the blue. If your eye tried to focus on ultraviolet as well, it would be even less focussed. ...

I might be wrong but this strikes me as totally incorrect.
I don't see blue text on a red background as vibrating. My eyes can focus on both. And focussing has nothing to do with the perception of color or vice versa.

[Paulhoff]

Originally Posted by Jeff Corey

I might be wrong but this strikes me as totally incorrect.
I don't see blue text on a red background as vibrating. My eyes can focus on both. And focussing has nothing to do with the perception of color or vice versa.

http://www.randomterrain.com/web-des...ckgrounds.html

Paul

[GoodGuysEatPie]

Originally Posted by Diagoras

Why did humans not evolve the capacity to see infrared light? Are there animals that can? It seems like it would be a great evolutionary advantage to see a predator's body heat in the dead of night. Could it just be a mutation that never occurred? Is there some sort of physical limitation on the wavelengths our eyes could perceive? Is it not as beneficial as my intuition says it should be?

I always think of it in terms of the range of wavelengths that would give us the most information. The Sun gives off light that is a spectrum across all wavelengths. However, because of its temperature, it gives off some wavelengths more than others: visible light. Our atmosphere effectively blocks out many of the other wavelengths (gamma rays, X-rays, most UV, much of the infrared (at ground level anyway)). Since infrared isn't the dominant light reflecting off of things, it doesn't make sense for us have an adaptation that allows us to see it.

If we were nocturnal, then it might. For humans, even during the primitive stages, I'm not sure there were many large carnivorous predators that were also nocturnal (maybe somebody here knows the answer to that). Because of that, I don't think it would have been a major advantage to have IR senstivity, even at night.

Now...if the Sun were a few thousand degrees cooler in surface temperature, we all might have adapted to see in the infrared...

~ggep~

[UserGoogol]

Originally Posted by JoeEllison

Well... it wouldn't be very useful compared to how much of a disadvantage it would be. Infrared vision in humans wouldn't be like switching night vision goggles on and off, it would be more information on top of the information we get from the visible light spectrum. Now, imagine seeing heat in the daytime near the equator, the infrared waves reflecting off of every object blurring everything into a nondescript nothing.

Speculating out of my ass, there's no particular reason why perception of infrared has to be treated the same as the typical red-blue-green, so that the brain could just ignore infrared information during the daytime or whatever. Of course, there are costs to having the brain do that sort of work, so it could easily be not worth evolution's while to go down that path generally speaking.

(Plus, I would imagine that generally speaking evolution would "try" to minimize the numbers of colors it has to focus on, (since the more colors you can pick up, the more cones you have to have, which wastes precious resources) and as such adding infrared would have to pay off fairly well just to justify adding more stuff to the eye.)

[Jeff Corey]

Originally Posted by Paulhoff

http://www.randomterrain.com/web-des...ckgrounds.html

Paul

Well. that site is dead wrong. Check their example of red text on a blue background. Does it "vibrate" for you?
The lens of the eyes focusses on a surface or object depending on the distance of that surface or object from the eye. Color has nothing to do with it.

[JoeEllison]

Originally Posted by UserGoogol

Speculating out of my ass, there's no particular reason why perception of infrared has to be treated the same as the typical red-blue-green, so that the brain could just ignore infrared information during the daytime or whatever. Of course, there are costs to having the brain do that sort of work, so it could easily be not worth evolution's while to go down that path generally speaking.

(Plus, I would imagine that generally speaking evolution would "try" to minimize the numbers of colors it has to focus on, (since the more colors you can pick up, the more cones you have to have, which wastes precious resources) and as such adding infrared would have to pay off fairly well just to justify adding more stuff to the eye.)

True enough... and, considering "color blindness", there's little reason to assume we'll even hold on to the color range we currently have. There could be a time in human evolution when we see fewer colors, not more colors.

[casebro]

Perhaps there is a range in which eyeballs work? It's a trade off- better high freq reception means worse low freqs? So what we have is a happy medium, considering the sun's frequency range?

Now don't confuse better night vision with IR either. Animals with better night vision have bigger eyes, bigger pupils, basically gather more light, over the same freq range. Or maybe they lose color vision all together, a lesser range, not a greater one.

[Paulhoff]

Originally Posted by Jeff Corey

Well. that site is dead wrong. Check their example of red text on a blue background. Does it "vibrate" for you?
The lens of the eyes focusses on a surface or object depending on the distance of that surface or object from the eye. Color has nothing to do with it.

Under low lighting it does vibrate when moved, I remember this happening to me as a child looking at a cardboard box with red letters on a blue background.

Sure your not red and green color blind.

Paul

[Paulhoff]

Also red and blue to not focus the same, I have camera lens that have marks for helping to focus infrared when using that type of film.

Paul

[Madalch]

Originally Posted by Jeff Corey

Well. that site is dead wrong. Check their example of red text on a blue background. Does it "vibrate" for you?

Yes, it does, actually.

Quote:

The lens of the eyes focusses on a surface or object depending on the distance of that surface or object from the eye. Color has nothing to do with it.

No, because the lens of the eye bends light to focus the image. It does this by refraction. The refractive index of the material depends on the wavelength of light being refracted (that's why prisms work). The wavelength of light determines the colour.

[wollery]

Most animals see in the visible range because that's where most of the Sun's energy comes out. It's why the Sun is yellow. Very little IR or UV make it to the ground, relative to the amounts of visible light. That's why IR and UV telescopes are best placed in orbit.

[Olowkow]

As promised, my friend who is living in Asia at present emailed me back this evening. He has been doing research on animal eyes for a long time. Here is what he wrote:

Quote:

As for infrared, most species evolve visual systems that use the predominant wavelengths available from the sun, as transmitted by the atmosphere, or by the atmosphere plus water for marine organisms. For example, depending on the nature of the water in which fish live (turbid, clear, salt, fresh, etc), the transmitted light differs significantly, and the fish that live in each kind of water have their receptor cells tuned to the local conditions. Some of this is genetic, but apparently some fish retain the ability to turn on and off genes for retinal receptor molecules to tune themselves to the local conditions should they change.

So, one reason that we don't have sensitivity in the infrared is that there's not much to see in the infrared anyway. Another reason is that the longer the wavelength, the lower the resolution, so that we would have poorer resolution for infrared.

This being said, some animals are sensitive in the near infrared. As you noted, the "pits" in pit vipers (like rattle snakes) are infrared-sensitive eyes. These don't have a lens, but form crude images like a pin-hole camera. These, however, are used to sense warm prey, rather than infrared imaging via the general illumination. Also, a lot of insects have sensitivity into the infrared and/or ultraviolet.

Hope this makes sense.

[Jeff Corey]

Originally Posted by Paulhoff

Under low lighting it does vibrate when moved, I remember this happening to me as a child looking at a cardboard box with red letters on a blue background.

Sure your not red and green color blind.

Paul

As I said in Post # 24, I might be wrong. But I do have plastic lenses where my old cataracts used to be. I don't see any vibration in the red on blue background. But any explanations involving difficulties focussing on red and blue because of prismatic effects strikes me as wrong.

[politas]

Infrared is a huge range of frequencies, far larger than the range of "visible light". There are some insects, such as bees which can see into the infrared spectrum further than we can (but only a tiny bit further, they don't have "heat vision")

We already have three different ranges of frequencies that trigger receptors in our retinas. No singe type of receptor goes even as far as our full range of visible frequencies.

The kind of "heat vision" the OP is talking about comes from a device which converts an large range of frequencies into a very small range which we can see. To get that kind of vision naturally (in gradations of discernable colours) would require a complex array of receptors in our retinas, with either so many different ranges that we would lose visual acuity, or else receptors which fired over very large ranges of frequencies, which would make daylight blindingly bright.

Even if you just wanted monochromatic "heat vision", you'd get that blinding effect during daylight.

[GreyICE]

Because evolution only produces models that are good enough. Infrared would help us, yes. And yes, we can design machines that see over that wide range of frequencies and still aren't blinded.

However, we can survive and reproduce without it, so it never got a chance to evolve.

[CaveDave]

Originally Posted by Jeff Corey

As I said in Post # 24, I might be wrong. But I do have plastic lenses where my old cataracts used to be. I don't see any vibration in the red on blue background. But any explanations involving difficulties focussing on red and blue because of prismatic effects strikes me as wrong.

AIUI, a simple lens (as opposed to a multi-element achromatic lens) cannot focus red and blue images in the same plane, one image being in-plane and the other more focused in front or behind of the sharpest image.

See Chromatic aberration

Dave

[Mr. Scott]

Originally Posted by Jeff Corey

I do have plastic lenses where my old cataracts used to be. I don't see any vibration in the red on blue background.

Thanks for mentioning that. You don't see vibration of red on blue because you don't have normal lenses in your eyes. The vibration for the rest of us is caused by the natural lenses struggling to focus on the red/blue pattern and oscillating between the focus points of the red and the blue. Plastic lenses used to replace cataracts have fixed, not variable focus and won't show the vibration.