by Matthew Cobb
I have a student who is writing a dissertation about the evolution of opsins – molecules that respond to light, which we use to see with. These molecules apparently have their origins deep in evolutionary time, long before there were animals, perhaps going back to 3.5 billion years, shortly after the appearance of life. While I was reading a draft, I wondered why organisms that use electromagnetic radiation for clocks and seeing (like us) and those that use it for getting energy (like plants, algae and cyanobacteria) all use pretty much the same part of the electromagnetic spectrum – the ‘visual’ spectrum. No organism can detect X-rays or radio waves (which are at opposite ends of the EM spectrum). Why not?
Unlike Jerry, I use Twitter, so I asked my tweeps why no organism can detect radio waves. Many of the answers fell into these three groups:
• What advantage would there be? Not much radio hitting the Earth.
• What emits radio waves that you would want to detect?
• Radio wavelength too long to provide differentiation at a cellular level?
The clearest answers came from two physicsts, @TommyOgden (a PhD student at Durham University), and from my friend and colleague @Tim_O_Brien, who is the Associate Director of Jodrell Bank radio telescope at the University of Manchester. Here’s my interpretation of what they tweeted. If they (or more likely, I) have made a mistake, chip in below.
Organisms use electromagnetic (EM) radiation to shift molecular energy levels, either for growth (photosynthesis) or in sensation (moving protons through cell membranes). Radio is too low-energy and has too long a wavelength to be able to move electrons from one energy state to another. At the other end of the spectrum, X-rays would be able to do this (they can excite the inner electrons), but there are not very many of them. Visible light is both highly energetic and is mainly what the sun produces.
So the simple answer seems to be – as you might expect – that life has been tinkering, making do with what it can find. The surface of the planet is covered with lots of this energy source, which is uniquely able to move electrons about, leading to the production of sugars in plants and sensory responses in animals (and other organisms).
Later on in evolution, other aspects of visible light – its directionality and its absorbability (?) by pigments led to the evolution of eyes, as areas of tissue shielded the detector from stimulation from all but a certain direction. If you were detecting X-rays, you’d have to ingest a lot of lead to be able to detect directionality.
One final point struck me, about quite how energy-poor radio waves are. Carl Sagan apparently said that all the radio waves detected by all the radio telescopes in the world were less than the energy released by a single snowflake touching the ground. Tim O’Brien was asked on the Jodcast (a podcast produced by Jodrell Bank) whether this was true. If you listen here at around 10:00, you can hear Tim work out the answer with some simple but occasionally mind-boggling sums.
If you don’t have the time, the summary of his answer is that the big dish of the Lovell telescope, detects 10-5 joules per year from Cygnus-A, one of the brightest radio-sources in the sky (800 million light years away). In comparison, a 50 watt light bulb produces 50 joules/second) Meanwhile, his guestimate of the potential energy released by a snowflake hitting the ground is 2x 10-6 joules. This is about five times less than the energy from Cygnus-A detected by Jodrell Bank in a year. So if any organism did have a reason to detect radio waves, it would have to be absolutely massive (much, much bigger than the Lovell telescope) to get any decent amount of energy out of it.
You can find an interesting discussion from a couple of years back of the evolution of transceivers, including references to various science fiction stories where people or animals could detect radio waves, here.
The bottom line of this story is probably the age-old evolutionary one of ‘if they could, they would; they don’t so they can’t’. On the other hand, at least I have a bit more of an idea of why – it’s all to do with physics, man.
h/t Tim O’Brien, Tommy Ogden and a Twitter cast of thousands (OK, six).
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Reblogged this on διά πέντε / dia pente and commented:
I always wondered about this
Wouldn’t 50 watts be 50 joules/second? How’d you get 650?
Yes. Typo will fix.
There’s also the matter of how much there is in the solar emission spectrum, which peaks in the visible; what it takes to excite almost any molecule (few undergo electronic excitations in the near infrared), and what the eye itself can transmit to the retina. So a good Q for Matthew’s students; how come we can’t see near UV but bees can?
If I’m remembering discussions on mammalian eyes vs avireptiles and arthropods, mammalian eyes have extremely poor color differentiation because the basil mammalian eye was evolved for good vision in low light situations where there wasn’t a good range of color being reflected anyway.
Humans are one of only a few species of mammals that are even capable of seeing in three primary colors rather than two, and I’m unaware of any non-primate mammals that can see in three primary colors.
Avireptiles (as in, the whole reptile clade including birds) and arthropods have remained primarily diurnal and thus have as a whole much better color vision than mammals. If I recall correctly, many birds can see in four primary colors, though the champion as far as color vision is concerned is the mantis shrimp: apparently, some species can see in as many as twelve colors.
Microraptor,that’s my recollection also. The low light would still be of good colour, if we could only see enough of it, but our most light-sensitive receptors do not discriminate between co9lurs, perhaps because they maximum sensitivity involves respinding to the widest possible wavelength range indiscriminately. But it isn’t actually relevant to why insects can see into the UV whereas we can’t.
I wonder, experiments have given rats trichromatic vision by giving them a gene for a different opsin.
Is it so simple that we could give animals UV opsins, but only insects & (some) birds vs plants have coevolved to utilize UV colors?
Torbjoern, do you have a reference for that work? Sounds possible and interesting, and I’d like to know more. Most mammals have two-colour vision, corresponding to our blue-green. A gene doubling event in green, followed by drift into a new function, gave old world monkeys and their descendants three-colour vision, so I presume there’s no physical reason why your enhanced mouse couldn’t be 3-colour.
I was just thinking of the short pathlength in the insect eye and the fact that protein absorbs near UV, albeit rather weakly. I have read that even two-colour vision can be traced to a yet earlier gene doubling event. So the cladistics of all the different optical opsins (I think there’s one organism with 11!) would be a neat little problem – I’m sure some work of this kind has been done already.
Indeed it has! http://genomewiki.ucsc.edu/index.php/Opsin_evolution:_trichromatic_ancestral_mammal
A complicating fiddle. The genes for one of the visual pigments are located on whichever of the sex genes it is that women have two of, to men’s one … OK, I worked it out ; must be the X chromosome, because Y genes trace paternity while mitochondrial DNA traces the maternal line.
Anyway, because of that, a small proportion of women with an uncommon ancestry inherit four different genes for visual pigments – the 2 non-x ones, plus two different alleles for closely related but different visual pigments. Which gives them tetrachromic vision, not normal trichromic vision.
At least one such woman has been identified, and when tested, her tetracromicity has been demonstrated.
Old news – about a decade ago – but a cool piece of genetics. Even I looked up from my fossils for long enough to remember some bits of it.
I suppose I’ll find seven better recitations of the story, with references, the moment I post this.
As I understand it, blue and green are carried on non-sex chromosomes, and red on X. Defective red is recessive. A female with one abnormal X will still have normal colour vision. But I’d really like to know more about tetrachromatism in humans!
I think trichromacy is fairly common in primates.
The interesting thing is that the receptors in reptiles (and fish) are not all the same as those in trichromat mammals. Trichromat mammals evolved from dichromats. One of their receptors is actually a recent descendent of one of the two dichromatc receptors, and has a different color (frequency) sensitivity than any of the ancestral receptors.
This reminds me of a Stargate Atlantis episode where the sea creature there could detect a solar flare building far enough in advance that they could hide in the shield of the city for protection.
Many animals are said to demonstrate irritability before an earth quake. Perhaps there are animals which are sensitive to non-visible light EM spectrum, but how would we know? There are British folk that claim to be ‘alergic’ to cellular signals. Why couldn’t animals also be sensitive in ways that we simply have not tested for nor been able to observe for the obvious reasons that such energy is not readily visible.
“There are British folk that claim to be ‘alergic’ to cellular signals.”
There are Americans who make the same claim. They’re crazy. It’s not real. It’s been studied.
I did say ‘claim’ ….
Plenty of birds and insects have been shown to have vision that extends into the UV range and quite a few fish are able to sense electric fields.
That may be, but low-frequency sound is a more likely earthquake signal. (What in an earthquake would be generating EM?)
I was only pointing out that there are senses that animals have that we are still discovering. Because we do not know of an animal which is sensitive to EM does not mean that there is not one or 70 that are. We manage to discover a new species every week or so, or find long thought extinct species etc. We know that animals have evolved some very special senses. Even if it is not likely we should not rule it out in this case. To wit: the god helmet experiment may have been hokey yet it does demonstrate a certain sensitivity to EM/magnetic energy in the mammalian brain. I think there was enough there to hypothesize that there are lots of portions of the brain which might be sensitive to non-visible spectra.
No, I would have no idea of how to test that, but it’s a thought. I’m more than happy to be proved wrong.
If you’ll allow me to put on my skeptic’s hat…
Re: “we don’t know everything so it’s possible”, which you are happy to be proved wrong about. I think that misses the point. For one thing, “it is possible” arguments are difficult or impossible to prove wrong. What matters whether the idea is _plausible_. After all, it could be true that somewhere there are arboreal pigs: we haven’t looked everywhere for them.
Oh, I agree with you. I think I fairly said I have not shown a good case for plausibility nor have I said I know how to test for it. I guess I should have said something like it doesn’t seem likely but we shouldn’t dismiss out of hand ideas that an animal is reacting to EM in some way. I would think that animals at the poles might be more likely to react in some way. Geese AFIK use a kind of compass to migrate. While the power levels of EM are low, there are ways to magnify the effect of the energy. Perhaps those animals living at the poles might have a better chance of interacting.
Yes, just because some animals use the magnetic field of the earth does not mean there should be animals who use other EM energy.
No, I have not shown plausibility per se. I don’t mean to suggest that it is highly probable, only that life on Earth has shown that if it’s possible to use a thing, it will get used… more or less.
Our forays into space have shown that human optic systems are sensative to other EM – astronauts see flashes of light when particles are detected, even if this is not well understood. The idea that animals could detect EM radiation other than light is not far fetched and does seem possible.
So a hypothesis that some animals use EM radiation for some reason would be odd, but ruling it out seems premature given the phenomena we have actually observed.
Fascinating. Thanks
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OT: As a Durham alumnus it struck me that Tommy Ogden has a very appropriate name for a Durham postgrad.
(Tommy, if you’re reading this, say “Hi” to Prof. Glover from me.)
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Well, the radio waves do not interact with molecules easily. Most of the organics are translucent to radio waves. I think that abundance of light from sun in certain spectrum and ease of interaction with molecules are the most important factors here. I would gladly see some comparisons using real data…
Really? Surely radio broadcasting requires more energy than that of a snowflake touching the ground, doesn’t it? If so, where does all that energy go? Is it just hopelessly diffuse?
Well, they are talking about natural sources, most of which are extremely low power because they are so far away. Signals from human made transmitters are much more powerful, but only because they are right here on Earth.
Actual modeling of radio transmission power losses over distance quickly gets very complicated, but in very general terms the loss is proportional to the square of the distance between the transmitter and the receiver (the surface area of a sphere is the basic starting point for modeling). So, yes the power of a radio emission diffuses quickly.
Yes, power is very diffuse at typical distances from a radio source. Transmitter power output (the energy in the radio waves themselves) ranges from 40W for an FM radio station that can be heard from 8-10 miles, to 20kW for some of the biggest stations out there. Imagine you were standing three miles away from the broadcast tower and had a ‘radio wave eye’ the size of your entire body. The amount of radio-wave power incident on your enormous eye would be only about 0.003 Watts. This is diddly-squat next to sunlight, which would deliver about 7,000 Watts to an eye that big! (And delivers about .003W through our tiny pupils.)
Besides, when evolution was happening, there were no radio towers, and thus the situation was even more extreme. 🙂
What an informative post. Thanks, Matthew.
What is the fraction of energy emitted from the sun infrared and ultraviolet (not visible) spectrum energy?
Astronomers model star emission as a simple blackbody spectra, modified by star atmosphere absorption bands. It is the blackbody peak temperature that sets the star temperature, our G2 sun having a ~ 5 800 K temperature. [ http://en.wikipedia.org/wiki/Sun ]
But, as Gregory Kusnick comments, it is mostly our planet atmosphere that decides what light reaches us. You could integrate the blackbody spectra but then the absorption physics complex – it is better to just find a spectral description of Earth’s daytime surface irradiance.
At the Earth’s surface here are the energy figures:-
5% UV [300-400 nm]
43% visible [400-700 nm]
52% near-infrared [700-2500nm]
Peak energy is in the visible band
A lot of animals are sensitive some way into the ultraviolet. Mammals aren’t, but many birds, reptiles, and insects are. The problem is that I don’t think there is much ultraviolet light and night, and the mammalian visual system is tuned to working at night and dawn/dusk, so the receptors that were not helpful for that were lost.
That’s a great answer. Obviously, there is some variation in where the boundaries of “visible” light lie for different organisms, but there had to be some reason that they are all in roughly the same range of frequencies.
Yep. For EM radiation, the shorter the wavelength the more energy per photon (its a wave and a particle, and a floor wax and a dessert topping!). Visible light packs enough energy per photon to be able to boost electrons to higher energy levels. Much shorter than that, however, and photons pack enough energy to start doing actual damage to biochemicals (e.g. UV exposure causing genetic damage that leads to skin cancers). If our planet was bathed in enough such high-energy radiation, DNA-based life would be impossible, at least on land.
So vision, photosynthesis, and other light-dependent processes can only use radiation that’s energetic enough to interact with matter, but not energetic enough to do much damage. On our planet, that’s also the majority of the radiation that reaches the surface from the Sun. This is not conincidental–life has evolved in the environment of this particular star and atmosphere.
‘Growth’ is of course only one of the products of photosynthesis. As for sensation, I don’t know a single mechanism of sensory transduction, certainly not vision, that involves ‘moving protons through cell membranes’. Maybe ‘ion’ is meant instead of ‘proton’? (Although the biochemistry of vision actually works by transducing EM energy into a decrease in sodium ions allowed to move across a membrane).
Another way of looking at the issue is by asking what information radio or X-ray would give an organism.
Radio waves pass through most things in the environment (at least most things the size of organisms), so even if one could detect them, they wouldn’t provide any information about what was in the environment. There’s evolutionary advantage to detecting something that doesn’t impact survival.
At the other end of the spectrum, X-rays and higher frequencies aren’t common enough, and so again don’t provide any useful information. (One might speculate that in a world with a lot of radioactive material on the surface, any organisms that evolve might develop sensory apparatus that makes use of it.)
I do not think radio waves conveyed much information useful to an organism before humans began broadcasting. Perhaps an impending thunder storm, but detection of compression waves does that adequately.
Interesting.
Related question: Why isn’t the ability to see IR and UV more common than it is?
Part of it has to do with atmospheric transparency, which varies by wavelength. UV is strongly absorbed by the atmosphere, as is most of the IR spectrum. The latter accounts for the greenhouse effect, in which visible light reaching the ground is re-emitted as IR, which cannot easily escape back to space.
Another factor is that IR vision would be of little use to warm-blooded creatures, whose own eyeballs emit enough IR to mask the emissions from other creatures. IR is good only for looking at things significantly warmer than you are (e.g. pit vipers hunting rodents).
Visible light occupies the sweet spot of peak solar emission, atmospheric transparency, and the ability to excite molecules without destroying them.
IR is a very good point. If you were a hunter of warm bodied prey then wouldn’t IR vision be incredibly useful? Personally I’m not knowledgeable enough to do more than speculate. I also couldn’t comment on its prevalence or scarcity in the Natural World.
And in fact this exists – pit vipers!
http://en.wikipedia.org/wiki/Infrared_sensing_in_snakes
That is awesome. Thanks to both Gregory Kusnick (who in many ways answered my queries before I posted) and Tyle.
When I read Gregory’s points I realised, “Of course, your own heat is all you’d sense!” But then Tyle pointed out that it could work well for cold-blooded creatures who hunt warm-blooded creatures. Fascinating.
And cheers for the link, Tyle. I love the bit ‘a blind rattlesnake can target vulnerable body parts of the prey at which it strikes’. Now there’s an evolutionary advantage if I ever saw one! (no pun intended!)
Not sure about UV. In order to detect IR, your receiver/detector must be kept cooler than the surrounding. In order to detect a warm bodied prey, the retina/eye should be cooler than the temperature of the warm body. This would mean keeping our eyes cooler than the rest of the body? Perhaps the inability of stumbling upon a suitable cooling mechanism is what prevents evolution from endowing organisms with IR vision.
In fact our own “eyes” in space suffer from this problem too. The ESA’s infrared space obesevatory – Herschel is about to run out of the liquid Helium that kept its detectors and science instruments at very low temperatures. That’s end of life for that spacecraft.
Didn’t read all the comments above! Gregory above makes the same point.
It is not correct that an IR sensor can only sense an object that is warmer than the sensor. Thermal imaging cameras do this all the time. The signal that an IR sensor outputs is the sum of the background from itself plus that due to external IR impinging on the sensor. Subtracting the background reveals the signal of interest. The IR wavelengths from a warm body peak at 10x to 20x longer than visible light and are hence 10x to 20x lower in energy which makes them difficult to detect by chemical means. Some IR sensors are cooled in order to improve the signal to noise ratio, usually because they are looking at very small signals.
I once took a nuclear engineering course. The professor said that students had found that Dyticidae would dive when exposed to gamma rays. He wanted me to pursue the matter, but I did not. When taking photos of insects with my digital camera, I noticed that some of the little dolichopodids seemed to sense the rays that the camera bounces off the subject in the process of auto-focusing and would be gone before the shutter tripped. Given the diversity of invertebrates, I suspect that there is a lot to be learned about what sorts of waves some of them can sense.
Gamma rays are energetic enough that they could be sensing them indirectly through a secondary effect of the gamma rays hitting matter.
Another great example of the question “Why is life this way? being answered by the response “Because it JUST IS this way.”
Far less satisfying to many, than the answer “Because Radome the Emitter deemed mankind unworthy of his X-ray blessings.“
“Because Radome the Emitter deemed mankind unworthy of his X-ray blessings.“
—
Peter Hitchens would say: “You may be right”
I’m afraid that I can’t really add anything useful to the discussion, but I would like to say thank you for a fascinating post (and subsequent comment section). If I may be so bold as to plead, more of these please! 🙂
The post is great, but the issue can also be usefully framed in terms of temperature:
http://en.wikipedia.org/wiki/Planck's_law
http://zebu.uoregon.edu/2003/ph122/bb3.jpg
The visible spectrum is potentially useful because there is a very large object nearby at the corresponding temperature (the sun). The infrared spectrum is also potentially useful, since there are lots of interesting biological objects at this temperature (not as big, but closer).
So, we get eyes that see sun-temperature light. And we also get eyes that mammal-temperature light!
http://en.wikipedia.org/wiki/Infrared_sensing_in_snakes
But can’t mammals and reptiles sense UVB radiation? Sure, we don’t form ultraviolet images with this sense but our skin undergoes chemical changes that stimulate the hormones that control circadian rhythms. And this is with some of the more high frequency types of UV rays.
?
I think you are confusing melanin with melatonin.
Hi Matthew. I hope you understand my point of view. I was thinking about light and photons. I’d like to ask your opinion. Do photons shine? Why do we see light?
Do you see? (Point of view)
No. The photochemistry of rhodopsin & iodopsin.
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I think that photons don’t shine, because otherwise we would be surrounded by the shine and couldn’t see anything but light.
I think that photons give impulses into the brain through the fine-tuned receptors. And the brain creates the image or the colourful landscape before the eyes wonderfully.
Sadly the bodily senses grow weaker.
http://en.wikipedia.org/wiki/Near-death_experience#NDE_as_proof_that_consciousness_can_function_outside_the_brain
But what frequencies of radio are we talking about? We’re constantly bombarded with radio waves from the air – and in fact the atmospheric emissions can interfere with astronomical observations, which is why instruments in space would be able to make observations which we can never make on the ground – but that’s true of the visible, UV, and infrared as well. Visible light is not only the most abundant form here on earth, but it is also the only one abundant enough to be of much use. UV works as well, but the fluorescence of many proteins and the damage done by the light due to its high energy make it less useful than plain old visible light. The same problem goes for X-rays – even if they were abundant enough, it’s doubtful they would be of any use to biological organisms in sensing or imaging their environment. Visible light is also refracted nicely by biological tissues and calcite, allowing animals to produce images with protein based lenses or calcite based lenses. Good luck producing an image with X-rays; it’s pretty tricky even when you know what you’re doing.
Another important factor in why life on earth reflects/absorbs only wavelengths in the visible range is that the elements of life (H, C, O, N) constrain the kinds of light that can excite our cells.
And, as we all know from Neil Degrasse Tyson by now, it’s not a coincidence that the most abundant elements in the universe are H, C, O, and N. This fact, coupled with the fact that our sun’s primary emissions are in the visible and ultraviolet range, suggests why radio-detecting organisms never evolved.
I recall someone, maybe George Gaylord Simpson making the argument that radio waves carried no useful information, and therefore there was no selection for being able to detect them.
Maybe we can rephrase this observation as follows: Organisms have three basic requirements, to find lunch, to avoid being someone else’s lunch, and to find a mate. Doesn’t seem to me that radio waves of any frequency would help any of these three.
FWIW, I just saw this on “Biological Fe oxidation controlled deposition of banded iron formation in the ca. 3770 Ma Isua Supracrustal Belt (West Greenland)”.
The erstwhile problem with Isua metamorphism having troubled fossil observations may have gone away, leaving an unambiguous biological signal:
“the metamorphism can neither explain the range in Fe isotope compositions across bands, nor that between hand samples.”
“the data can be well modeled by anoxygenic photosynthetic Fe(II) oxidation.”
So likely photo-utilizing biochemistry going back at least ~ 3.8 Ga bp,* consistent with a roughly ~ 3.5 Ga bp origin.
Physics, the elephant in the biological room.
* Of course, such early photosynthesis could strain timing of earliest life, now often considered as ~ 3.8 Ga bp even without the above putative fossils. Even simple anoxygenic systems had to have a lot of ion pumping membrane machinery in place.
Biology – the gnats in the physicist’s Brontosaurus pen.
Sorry, “Apatosaurus“
Well, I do like the thermodynamic results on RNA and replicators recently.
Before that, and outside of vision and size scaling, not so much. :-/
Illuminate me. This doesn’t quite trigger my braincell.
I’m surprised to have been the only one to remember the tetrachromats. Oh well.
Not the only one, but I couldn’t remember more exact details and haven’t googled it yet. 🙂
Related, but static (source dependent) sensing/signaling: electrostatic sensing & communication, magneto-“static” taxis.
I had always imagined that it was due to two effects:
First, the visible spectrum is the only region of the spectrum where water is transparent. If you look up a plot of water’s absorbtion spectrum, you will see very dramatic trough right around the visible spectrum. Frequencies even slightly higher or lower than visible are highly absorbed by water (which is why microwaves heat moist things so well). If early life was in the ocean only light in the visible spectrum would reach it, as seen in this plot: http://arthropoda.files.wordpress.com/2010/04/attenuation.jpg
Second, the sun’s spectrum peaks right around the visible spectrum. Thus, most of the light available for vision and energy comes to us at visible frequencies.
As was mentioned earlier, many animals can see well outside the human “visual” spectrum. The problem is that the mammalian visual system was tuned to night and dawn/dusk conditions, so we lost a lot of the color range that our closest relatives have.
To put it another way:
4 color receptors (other tetrapods) -> 2 color receptors (mammals) -> 3 color receptors (primates)
And note that one of the 3 primate color receptors is a descendant of one the other two, it is not the same as any of the original tetrapod receptors.
Not only that, but there are UV-sensitive aquatic creatures. For example the mantis shrimp sees well into the infra-red and ultraviolet, in fact it has better color discrimination in the UV range alone than we have in total.
That’s possibly putting the cart and the horse in an inefficient geometrical configuration for propulsion of one by the other. Surely our visual system has developed to use the most abundant available form of radiation.
I’m trying to think of a cat simile. “Putting the kibble behind the kitty”? “Letting the cat out to play in the snow”?
Very interesting post.
There is one thing that has been omitted- the ‘imaging resolution’ that one can achieve with light is much finer than radio frequency. Think of features that organisms can sense. Radio frequency can only resolve at the coarse level of a few centimeter of resolution. This may have been too coarse for early organisms to make much sense out of. The underlying reason for this being useless of course is outlined in this blog post, but I think at a higher level, the concept of imaging resolution is germane to the discussion.
Good point! A rule of thumb for imaging resolution is the Rayleigh criterion, which is computed as:
sin(theta) = 1.22 * wavelength/aperture diameter
where theta is the angular resolution. Even if we only consider very short wavelength radio waves, say 1mm, a typical human-size pupil of 6mm in diameter will only give an angular resolution of 11.7 degrees! Using a middling visible light wavelength of 550nm, a perfect eye with a 6mm pupil has a resolving power of .006 degrees or about 20 arcseconds! To get the same resolution from the 1mm radio wave, you need an aperture that is almost 11 meters in diamter! Thats a big pupil!
On the other end of the spectrum (literally!), a 6mm pupil focusing x-rays of 1nm wavelength would give an angular resolution of .00001 degrees or .04 arcseconds.
For radio detection to be an advantage, it’s not essential that there be a lot of radio flux in the environment from abiotic sources like the sun. Looking at the stars (or more energetic extragalactic sources) is probably not enough of a function for evolution to build an imaging system, but what about a radio sense that’s only weakly directional, more like smell than sight?
Body size is a problem; most animals are smaller than most radio wavelengths, so can neither ‘see’ nor be ‘seen’ in them. But given that many animals have been shown to have mechanisms for detecting weak electric fields, and some for emitting strong ones, it’s not really obvious that radio communication is not occurring in some species. How hard could it be to grow an antenna, or a parabolic dish, out of biological materials?
Off topic, but I notice that the structure holding the antenna in the focus of the Lowell radio telescope is a small version of the Eiffel tower–probably mathematically the optimal shape for a light but rigid structure.
Well, sure. If you take a vertical slice through a dam or a nuclear power plant cooling tower, you’ll see the same shape again. Or graph atmospheric pressure as a function of altitude: same again.
The thing they all have in common is that the structure at any given altitude has to support the weight of the entire structure above that altitude. The solution to that equation is an exponential curve.
Back to evolution, am I right thinking that there are bone structures that also have exponential shapes?
Well, the thing is that there aren’t many animals shaped like vertical towers, although I suppose a giraffe’s neck might qualify.
We probably need a photochemist here. From my understanding, as you move from the visible to the infrared (ther is a little more output from the sun here than in the visible), transitions become increasingly degenerate. As pointed out by others,sensitivity to ever shorter wavelengths (UV) exposes molecules to higher energies and greater chances of damaging photoreactions.
Photon detection systems based on far UV or infrared may well have evolved in the past. That they do not exist today suggests that they did not provide sufficient advantages in the ecosystems of their time that they would have descendants. The reasons may involve degeneracy in the infrared, high energy in the far UV.
Radio waves? Maybe they would be a much better “solution”, but evolution does not work to solve problems, just random possibilities based on the organics at hand at the time.
Femiglab says:
“Radio waves? Maybe they would be a much better “solution”, but evolution does not work to solve problems, just random possibilities based on the organics at hand at the time.”
Even if we evolved some kind of radio-wave vision, the resolution ~~wavelength, would be miserable, we wouldn’t even be able to find our front door.
Resolution isn’t everything though. Simply detecting light or dark was good enough for early organisms.
“why organisms that use electromagnetic radiation for clocks and seeing (like us) and those that use it for getting energy (like plants, algae and cyanobacteria) all use pretty much the same part of the electromagnetic spectrum – the ‘visual’ spectrum.”
“Radiotrophic fungi are fungi which appear to use the pigment melanin to convert gamma radiation into chemical energy for growth.”
http://en.wikipedia.org/wiki/Radiotrophic_fungus
Fascinating, as Spock said. I will read the PLoS ONE article the Wikipedia entry is based on (always go back to the source!) and post again, with Jerry’s permission (it IS his blog, after all…)
Indeed, it’s interesting to look at the shape of the energy coming from the Sun that arrives to the Earth though the atmosphere.
For example, here:
http://www.ucar.edu/learn/images/spectrum.gif
The visible light is the less attenuated and therefore the organisms are more adapted to detected the radiation in that band.
Even more interesting, if we look at which *colors* it attains its maximum, we observe that it’s in the green. The minimum is in the blue.
Therefore, our eyes can detected easily the green, much more than the blue.
Moreover, our eyes have much more cones dedicated to detect the green color than the blue.
Two articles published on-line in Nature today:
Kirschvink, J.L. Sensory Biology: Radiowaves zap the biomagnetic compass. Nature (2014), doi:10.1038/nature13334,
and
Engels, et al., Anthropogenic electromagnetic noise disrupts magnetic compass orientation in a migratory bird.
Nature doi:10.1038/nature13290