Cephalopod camouflage, or: turning invisible is easier than it looks

i-82e420e4939b377f9fc00c2e618c326a-octo_camo.jpg
Octopus vulgaris reacting to a diver (predator).

The initial change from camouflaged to conspicuous takes only milliseconds due to direct neural control of the skin. Full expression of the threat display (right) is two seconds. Video frame rate is 30 frames per second. Watch the video clip.

Everyone here is familiar with the incredible ability of cephalopods to change their appearance, right? If you aren't, review your cuttlefish anatomy and watch this video. A few frames from the video are shown on the right.

This is an amazing ability, and the question is how do they do it? Roger Hanlon has been spending years tinkering with cephalopods, trying to puzzle it out and come up with an explanation. There are a couple of things a master of disguise needs.

  • A good visual system. To match the background, you need to be able to see the background at least as well as the predator trying to see you.

  • Fast connections to the effector organs. Cephalopods have motor nerves that go straight from their brains to the chromatophore organs with no synaptic delays along the way.

  • The hard part: cutaneous chromatophore organs that can change intensity and texture with a fair amount of spatial resolution. Cephalopods have tiny, discrete sacs of pigment scattered all over their body, each one ringed with muscles that can iris shut to conceal the pigment, or expand the sac to expose the pigment. There are also muscular papillae that work hydrostatically to change the texture of the skin from smooth to rough to spiny/spiky.

  • An algorithm. A set of rules that translate a visual field into an effective skin pattern that hides the animal.

One of the minor surprises of this work is that that last item, the algorithm for generating camouflage, may not be that complex. By studying many camouflaged organisms, they've categorized camouflage techniques into just three different strategies.

The three are responses to the coarseness of the patterns in the environment. If the background is fine grained and simple, blend in by generating a uniform skin pattern that matches the average intensity. If the background is a mixture of small objects of varying intensity, take on a mottled appearance to blend in. And finally, if there are relatively large objects with a fair amount of contrast around, instead adopt a disruptive camouflage scheme, which has the function of breaking up the outlines of the body. These three categories are illustrated below.

i-265094f6be76bb19af6bff6bed175e8e-camo_patterns.jpg
A visual sensorimotor assay for probing cuttlefish perception and subsequent dynamic camouflage.

Row 1: visual backgrounds with different size, contrast, edge characteristics and arrangement are perceived by the cuttlefish, which quickly translates the information into a complex, highly coordinated body pattern type of uniform, mottle or disruptive (left to right in each row of photographs). Row 2: examples of how small sand particles elicit a uniform pattern in Sepia officinalis; slightly larger gravel particles of varying higher contrast elicit a mottle pattern; and large light and dark particles elicit a disruptive pattern. Row 3: simple visual stimuli -- such as uniformity or small to large high-contrast checkerboards -- can elicit uniform, mottle or disruptive camouflage patterns in cuttlefish. The chief difference in the latter two backgrounds is the scale of the checker. Both the visual background and the body pattern can be quantified so that correlations can be made between visual input and motor output. Row 4: enlarged images of the uniform, mottle and disruptive body patterns. Note especially the diverse shapes, orientations and contrasts in disruptive.

Hanlon was also testing their abilities experimentally by placing cuttlefish on computer generated backgrounds and challenging them to try and match them. As you can see, they don't do as well as they do on natural textures, but you can also see how what they're trying to do fits in with the categories. Note in the bottom right that the animal really isn't trying to make an exact duplicate of the checkerboard pattern below it—it has created a pale square in its midsection that isn't aligned with the grid, but in a natural environment would catch the eye of a predator as a white square, rather than a tasty cuttlefish.

Another interesting observation is that cephalopods are thought to be color blind—they have one visual pigment with a peak sensitivity at 492nm—and that was tested with checkerboards of various colors but similar intensity at 492nm, and the cuttlefish can't see them. A checkerboard of blue and yellow squares that is painfully contrasty to our eyes is seen as a uniform gray by the cephalopod, which then adopts a uniform gray-brown skin color. How they do any kind of color matching is not known, but it may be that they simply don't: in an environment lacking many bright primary colors, sticking with natural shades of gray and brown may be adequate.

They may not have color vision, but they do have an ability we lack: the ability to see the plane of polarized light. Their skin also contains a class of pigment cells called iridiphores that are under neural control and that reflect polarized light through the overlying chromatophores. Changes in the plane of polarized light would be completely invisible to us, but quite apparent to the cephalopods—they could be sending secret signals to one another right under our noses by subtly rotating their iridiphores.

The lesson is that there are sneaky subtleties in cephalopod capabilities, but the general principles of camouflage aren't particularly elaborate—the eye is easy to fool, and just a few general strategies are sufficient. Of course, you still need a fairly elaborate array of controllable pigment elements in order to implement those strategies.


Hanlon R (2007) Cephalopod dynamic camouflage. Current Biology 17(11): R400-404.

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The obvious prediction is that there are some predators whose visual systems have adapted to more primitive forms of cuttlefish camouflage. Any guesses?

Great!

When I was in (aw, explaining this to a non French is near imoossible) well, in something like a special intensive undergrad class in biology, a group of student chose cuttlefish camouflage as research project.

The poor beasts were awfully stressed out and tried to commit suicide by repeatedly colliding with the tank, thus breaking their "bone". but the experiments were extremely cool.

People have probably seen this already, but there's a great cuttlefish invasion off of California:

javascript:cnnVideo('play','/video/tech/2007/06/06/johnson.ca.jumbo.squid.kcal','2009/06/05');

The patterns all look symmetrical, but I'd have thought that would increase apparency to a predator versus an asymmetrical pattern. Is it because of the direct nervous connections to the chromataphores - maybe the same source controls both sides?? Or to reduce the processing required?? As you can tell I don't know much about the wiring in cephalopods.

Whoops, I should have said 'squid', not 'cuttlefish' - don't know where that came from. This is what happens when you let a physicist prattle on about biological topics he knows nothing about. Hmm... maybe I should apply for that DI job...

Sorry to show my ignorance,but do we know how their ability
to change appearance evolved?

Awesome. Even though chuckling at creationists is fun (and culturally important), this is the sort of thing that really makes Pharyngula engaging for me.

I'll second Mel's curiousity about the structure of cephalopod nervous systems. Are there specific, exotic brain structures devoted to chromatophore management? What about skin texture adjustment and mimic behavior (which may be more complex than basic camouflage?

What will really get me excited will be when someone manages to graft or grow a mouse with chromatophores!

By Spaulding (not verified) on 06 Jun 2007 #permalink

This comment is not directly about cephalapods.

I am curious about the fact that the somewhat related site site Panda's Thumb has been shut down today. I know they have been subject to attempted attacks by pathetic, cowardly, authoritarian-wannabe creationist trolls who can't handle the truth recently.

Does anyone know what's going on, and if there's anything anyone can do to help?

I once had the opportunity to observe a small octopus in a tidepool use its camouflage abilities; a literally jaw-dropping experience. I'd read about this subject, but to actually see it... Just astounding.

Thanks for the essay, PZ.

Harold: according to Reed Cartwright over at De Rerum Natura,

"We're having issues today with the Panda's Thumb's server over heating. We are trying to let it cool down so we can access it remotely.

We have a new server nearly ready to go, and we can press it into service if necessary. We're not using it yet because we are deploying a new layout for PT at the same time we deploy the new hardware. We are also switching from MySQL to PostgreSQL."

Great post! Color perception may not be as important beneath the sea, especially the deeper you go, as much of the reds get filtered out and most things are sort of blue or brown. Most of the stunning underwater photos you see are taken with an extra light source which brings back int the bright colors.

They may not have color vision, but they do have an ability we lack: the ability to see the plane of polarized light.

Do we lack that ability? What about Haidinger's brush?

(Then again, I've never been able to see Haidinger's brush)

DaveX:

Photons (particles of light) have a polarization, which can be thought of as whether the particle is oriented vertically or horizontally. Our eyes can't tell the difference but apparently it's not difficult to build a filter that blocks one but allows the other. Or to generate photons with a specific polarization - I remember television broadcasts in the mid or late 80s that used the polarization effect to create 3D movies (you needed special lenses to see the 3D effect of course, and the effect was mild and slightly headache-inducing, which is probably why they stopped doing it. Maybe we'll see them try it again with HD.)

You've probably seen polarized sunglasses for sale - if not, next time you're at the department store, check out the sunglass rack and see if they have 'em. By allowing through only photons that are oriented a certain way, they effectively block 50% of the light, but you'll notice if you stack a few of the lenses behind each other (with the same orientation), you can still see through two or three polarized lenses about as well as you could through one. However, rotate one of the lenses 90° and the result is total opacity. Neat and weird stuff.

The ability to camouflage required an algorithm? Like a computer algorithm? Computer algorithms require intelligence to write. Therefore, cephalopods must be INTELLIGENTLY DESIGNED!!!

[/UD]

By carlsonjok (not verified) on 06 Jun 2007 #permalink

#10: ""the ability to see the plane of polarized light"

What does this mean, exactly?"

Assuming you are asking about what the plane of polarized light is, and not the finer question of how they see it, I can give you an answer:

Light has wave properties, much like water waves or waves on a string (or a long coiled telephone cord). More important for our discussion, light waves are transverse , which means they wiggle up and down in directions perpendicular to the direction the wave is traveling. On a long telephone cord, you get transverse waves by snapping the cord up and down - the wave travels away from you horizontally, but the vibration is in the up/down direction. (The other type of wave - longitudinal - can also be made on a phone cord, by grabbing a section of cord, pulling it towards you, and releasing.) Of course, we can make transverse waves in many different ways: wiggle the cord up and down, or alternatively left or right, or at any diagonal. The direction of 'wiggle' is what we call polarization. Light coming directly from the sun is unpolarized , which means it contains equal parts of up/down, left/right vibration: our eyes haven't evolved polarization detection ability because most of the light we see is unpolarized, and there's no useful polarization information to be gained from it. (Many sunglasses, however, are designed with polarizing lenses which block either up/down or left/right waves).

Why would a cephalopod need this ability? One reason was given by PZ (communication?) but another reason is that the transmission of light through an interface (e.g. from air to water) is more or less depending on its polarization. Light reaching a 'pod from the surface would have some polarization dependence, and could provide useful information to the sea dweller, perhaps orientation info?

http://www.polarization.com/octopus/octopus.html

is a good reference on polarization in cephs.

I think it's worth noting that although the choice of 3 very effective patterns shows that their algorithm reduces to a few common and effective patterns in particular camouflage situations, the repertoire of these animals is much larger than that, and also includes skin texture, and in addition to the direct nervous control over chromatophores, they have passive leucophores, and there is evidence that they can control their own polarization actively with their iridophores.

Hanlon is usually in the "seek simplicity" camp, and expresses skepticism in his book about Moynihan's claims that sepioteuthis has a complex visual language for communications, but there's no question that cephs use many more than three displays, for camouflage, surprise, escape/distraction, intimidation, and some level of communication with conspecifics.

Withholding judgment on what purpose exactly is involved in the displays, it's worth noting that there is a very large repertoire in reef squid which has been partially documented here: http://www.byrne.at/squidmodel/ and cuttlefish have a similarly broad range of active patterning, so although the mottle patterns are preferred for most resting camouflage, to say that the algorithm breaks down to "look at the scenery and choose one of three" is an oversimplification.

And to Spaulding: yes, there are whole brain lobes devoted to controlling the chromatophores. There are some rough experiments that suggest there is a somatic map of the animal's skin on these lobes (electrically stimulating the front of the lobe causes the front of the animal to change color, and the back similarly). See Nixon & Young or Hanlon & Messenger for various gory details.

Mel: although most patterns are symmetric, that's not hard-wired. In fact, in mating, there is a phenomenon of "sneaker males" that show male mating displays on the side facing the female, but "I'm a passive female" displays to the larger aggressive males on the other side. In a more subtle example, they can do countershading to take the direction of sunlight into effect in their camouflage behavior. In fact, there is a separate chromatophore lobe on each side, and it's possible to de-enervate one side of the animal's chromatophores and leave the other alone. I don't know if it's been studied how these lobes communicate with each other, or how the visual lobes contribute their perception of the background to the chromatophore lobes-- presumably, the left chromatophore lobe wants to match the pattern the right eye sees and vice-versa, so there's probably some crossing over between them.

Sailor @ 13,

I remember reading something like that in a recent National Geographic. So I searched it, and here's the article I found, along with the photo gallery. I seem to remember a picture from the magazine that isn't available online, where they showed a direct comparison of a photograph of a particular scene taken with and without flash, to show just what a difference it made.

One theory the article mentions is that at least around reefs where there are lots of animals, the bright colors and high contrast act in a similar manner to zebra stripes, making it hard to distinguish individuals from the background. Only in reefs it's lots of species doing it, not just one.

I think (but do not know) that this is roughly analagous to our ability to hear (without realizing it) phase differences in sound, which enables us to determine (without thinking about it) from where, in 3D space, a sound is emanating. We take this ability for granted, but it's not intuitively obvious how any creature with only two ears, one on each side of its head, is able to know whether a sound is coming not just from left, right, front, or back, but also from above or below. (Psychoacoustics is one of the many things that interest me far beyond the scope of my knowledge of them...!)

So, might a creature that can detect the plane of polarization be more able to readily and quickly perceive the surface detail of an object (its texture and relief) without relying solely on stereopsis or monocular cues as we do?

Does anybody know if cephalopod bioluminescence
is performed by a variant of the chromophore organs,
or is this carried out by another pathway entirely?

By Dark Matter (not verified) on 06 Jun 2007 #permalink

Excellent, PZ, and fascinating and thoughtful comments, as well, folks! Thanks!

By Steviepinhead (not verified) on 06 Jun 2007 #permalink

Kseniya-- The frequency of the sound gives us a lot of clues as to the position. The composer Karlheinz Stockhausen once wrote that he was curious as to how he was able to tell the apparent position of birds outside his window without actually seeing them. Upon closer listening, he realized that that some of the higher frequencies of the chirping were lost as the bird moved below his window, with the opposite happening as the birds moved above. Do some careful listening, and see for yourself! I imagine this is due to the shape of the human ear. Another interesting phenomenon is the perception between volume and amplitude. Because our ears are "tuned" in some fashion to hear the human voice, it can often be perceived as being much louder than a sound which actually has a greater amplitude!

all the cool adaptations got taken by other species

Yes, and I noticed that cuttlefish is also awash in redundancy. Not only multiple arms and suckers, but according to the anatomy lesson three hearts, two of which serves the gills. (shakes head)

DaveX:

Light can be polarized, which can be used by animals for orientation.

gg covered the physics in a better way already, but since I composed this answer it may contribute:

Polarization is a description of the perpendicular oscillation of a general transversal wave. A longitudinal wave (oscillates in the direction of travel) such as sound has no polarization.

The wave picture of light is complicated by that EM waves have two components, E and M fields. But they are coupled (perpendicularly, btw) so a polarization description is still possible. (In the QM picture as one can surmise the spin of the photon is coupled to the polarization.)

To make a long story short, normal light sources are non-oriented so we observe equal polarization in all directions, circular polarization. But reflections (such as against water surfaces) or scattering (such as in clouds) change that, and we observe oriented elliptical polarization.

One use is that animals such as ants and bees seems to be able to orient themselves from observing the sky even on cloudy days. By using polarizers we can do the same, see the link to Haidinger's brush above, or look up the somewhat controversial Viking sunstone in Wikipedia. Another use is that polarization glasses cuts down the glare of reflections.

Btw, http://en.wikipedia.org/wiki/Polarization seems to be a good resource covering all of this, the description of the basic plane wave, et cetera.

gg:

our eyes haven't evolved polarization detection ability

Well, see the link to Haidinger's brush. But the poor detection some (most?) people may have seems to be incidental (attributed to dichroism of pigments in our oriented organelles it seems), that is for sure.

By Torbjörn Larsson, OM (not verified) on 06 Jun 2007 #permalink

DaveX: Very interesting! Yup, the frequency response curve of the human ear is anything but flat. (Obviously the Great Designer *cough* knew we'd have a need for dog whistles one day.) Those low-frequency sound waves can pin a meter or blow a speaker without sounding anywhere near as loud as a mid-rangey sort of instrument like an electric guitar.

I believe there is also a perceived (not actual) distortion of pitch at very high amplitudes. Our readers who have some experience playing (or listening) to very loud rock music may have experienced this.

The directional characteristic of sound decreases with frequency, and low-frequency sounds seem to "come from everywhere" (and nowhere) but everyone knows how hard it is to pinpoint that barely-audible yet very-annoying ultrahigh-pitched whine coming from a computer or monitor. That our cognitive abilities are optimzed for sounds that occupy the middle of the audible frequency spectrum is hardly surprising, and evolutionarily obvious, at least at a glance.

Some of you may know the wonderful Douglas Adams story from Last Chance To See about the flighless bird (in NZ?) whose mating call was a very low-pitched sort of throb, perhaps not unlike a muted bass drum. The bird had no natural enemies in its habitat, and had evolved a very low reproduction rate involving single-egg clutches and a difficult-to-locate mating call. Things didn't go well for this bird after the introduction (by man) of rodents and canines...

Re: Stockhausen. It's also important to note that the location of a sound source in the space in which it is heard also makes a difference in how we hear the relative proportions of the frequencies that make up the sound. Low freqencies are reinforced by reflective surfaces. This is audiophile stuff, but it happens to be true. Position a speaker in the geometric center of a room (on a stand, or hung from the ceiling) and it will sound thin. Place it on the floor in the corner, and the low frequencies will be much stronger (and the high frequencies, though essentially unchanged, will seem weaker by comparison). Also, high frequencies don't go around corners (or thru walls) as readily as low frequencies. Perhaps these factors had some effect on what Stockhausen experienced. Bird closer to the ground might sound fuller (and correspondingly less bright) than those in the air, particularly if they'd dropped out of line-of-sight.

#25: "Well, see the link to Haidinger's brush."

I was completely unaware of that phenomena! I can't see it, though with the quality of my eyes I'm lucky to see anything at this point.

"To make a long story short, normal light sources are non-oriented so we observe equal polarization in all directions, circular polarization"

A little nitpick of your comment: normal light sources are unpolarized which is different from circular polarization. To use my vibrating phone cord example from #17, circular polarization would involve swinging the cord in a circular path, which would result in a somewhat helical-looking wave traveling down the string. A state of unpolarization would involve randomly changing between wiggling the cord up/down and wiggling it left/right (or, alternatively, rotating clockwise and counterclockwise). Unpolarized light is associated with some amount of randomness, which comes from the random nature of the atoms which produce the light (sometimes the atoms `feel' like radiating up/down, sometimes they `feel' like radiating left/right) - over a long enough period of time, you've seen the wave wiggle in every direction.

Well, even if cephalopods are color-blind, their predators obviously are not. Many fish have tetracromatic or even better vision meaning they see much more colors than mammals, humans included.

By Dunkleosteus (not verified) on 06 Jun 2007 #permalink

Damn, PZ-- that bit about the simplicity of camouflage algorithms is actually pretty reassuring. Tough for me to explain why, but it is.

PZ, thank you very much for posting this. I will somehow fit this into the magicalness of how cephalopods were intelligently designed. It is not humans, as those Bible toatin Christians have us believe, that are masters of our domain. The Great Cephalopod simply messed his mark the first time when communicating with the highyl intelligent creatures. Nay; it was the cephalopod whom named the animals in the garden.

I mean, come on. It's obvious that we live on a priveleged planet for the cuttlefish, the squid, and the octopus. We're mostly ocean and there is wider biodiversity in tastey treats in the wide blue wonder. Land masses and us naked apes are consequences to the Grand Design ;-)

Wow, I can totally see Haidinger's brush on my iMac screen -- thanks for that link!

@22 -- for a while as an undergrad I worked with a bioluminescent squid, Euprymna scolopes -- its bioluminescence was from a specialized organ that contained symbiotic bioluminescent bacteria! As if squid weren't incredible enough. I'm not sure if they all do it this way though.

Years back, diving near a shallow reef in Washington State, I had the experience of watching three Great Pacific octipi "uncloak" from the textures and colours they had adapted to blend in with the soft corals on the rocks they were attached to.
The effect was as astounding as if they had materialized via a Star Trek transporter beam, though somewhat slower. It was like they had appeared out of thin air. Err, thin water.

"One of the minor surprises of this work is that that last item, the algorithm for generating camouflage, may not be that complex. By studying many camouflaged organisms, they've categorized camouflage techniques into just three different strategies."

Not so surprising as beautiful. As an engineer, I always appreciate an economy of means. Occams razor works in evolution as well as in any other logic. As a software engineer, I know a human attempt to design the set of algorithms would have begun by assuming 10 were necessary.

I understand about using visual clues to aid in camoflage, but when they are resting on a rock or something, how do they see what it looks like behind them ? ( dumb layman question #1 )

look where their eyes are positioned.

not on the front like yours.

moreover, each eye has a much wider degree of vision than yours do.

they can basically see 360.

Speaking of economy of means, I'd bet that somewhere pretty early in the cuttlefish visual system are neurons with a spatial resolution that corresponds EXACTLY to the threshold at which they change from uniform to mottled camouflage, and another for the mottled/disruptive threshold.

The whole camouflage circuit could only be a few neurons long.

Thanks Ichthyic, I see now !

Colbert just had a segment on octopi:

"Whenever I go camping near a body of water, I spend a lot of time octopus-proofing my food. Put it in a bottle with a twist cap, and you're safe from octopi, squid, and kraken.

Or so I thought. An octopus at the National Aquarium in New Zealand has learned how to open a plastic bottle with its tentacles to get at a snack inside. Of course, the aquarium staff are treating it like it's a good thing, but I say narrowing the gap between cephalopods and humans can only end in disaster."

I'm sure there'll be a video of the segment any minute now, but I was already here at Pharyngula, so...

By Chinchillazilla (not verified) on 06 Jun 2007 #permalink

A little nitpick of your comment: normal light sources are unpolarized which is different from circular polarization.

D'oh! You are right of course.

Actually, I think I have conflated these two for a very long time, so I run right into that one without thinking too much. I should have taken my own advice and refreshed the basic plane wave. :-o

Slightly embarrassing actually - I was a course assistant (in the lab) for an optics course a while. (I was rather good at it, so I had to take the darnedest slots at short notice.) But OTOH it is good to get one less confusion to drag around. Thanks!

Hmm. I don't know where to get a phone cord any longer, but I would probably benefit from pulling out a wire and start playing. Seems the simplest analogies are really the best. (Feynman knew this, I'm sure.)

which comes from the random nature of the atoms which produce the light (sometimes the atoms `feel' like radiating up/down, sometimes they `feel' like radiating left/right)

Yes, atom or molecular electron (EM emitting) orbitals has some spherical symmetries, even if not equally probable to emit radiation in every spatial angle.

But also important is that in most emitter materials the shell directions average out as well. By polycrystallinity or by being gases for example.

By Torbjörn Larsson, OM (not verified) on 06 Jun 2007 #permalink

Amazing what millions of years, and natural selection acting on random variations are able to "create".

/darwinian cherry

@ Kseniya:

The fundamental frequency of a sound is a physical characteristic; its pitch is a human perception which is primarily, but not completely, determined by fundamental frequency. In the range where our hearing is most sensitive- a roughly 1- octave band centered on 2kHz- the perceived pitch of a tone varies little with changes in loudness. At low frequencies, the perceived pitch of a tone will be lower at high intensities than low; at high frequencies the perceived pitch of a tone will rise with increasing intensity.

The relationship of pitch to fundamental frequency is also nonlinear, with changes in frequency having less effect on the perceived pitch of a note at high and low frequencies than in the midrange. Piano tuners have to "pull" the tuning of the high and low strings away from the values predicted by the math of the equally-tempered scale to get the piano to sound in tune- the high strings have to be tuned higher and the low strings lower than the predicted values. This is one reason why a good piano tuner works primarily by ear and not by relying on a frequency measuring device like a strobe tuner.

It's been shown empirically that the spectral range most critical to speech intelligibility is the octave band centered at 2 kHz. Interestingly, our hearing is most acute- in absolute sensitivity (the lowest SPL that can be perceived), ability to discriminate small differences in pitch and to discriminate small differences in intensity- right in that frequency range. The length of the average adult ear canal is such that it provides optimal matching between the low characteristic acoustic impedance of the open air and the relatively high impedance of the eardrum in that same frequency range.

Our ear-brain system is rather nicely adapted to understanding our own species' acoustic communications. This isn't surprising- the selective benefit of being able to understand "Og! Look out for the bear!" the first time isn't hard to imagine.

BTW, our brains use a variety of cues- differences in intensity, differences in time of arrival, differences in high-frequency content, between the signals received by each ear- to sort out the location of a sound source. There's even good evidence that comb filtering produced by reflections from the folds in our external ears play a role in high-frequency localization.

By Ktesibios (not verified) on 07 Jun 2007 #permalink

My wife wants to know if she can use Haidinger's brush on Schrödinger's cat?

I'm putting together a presentation regarding the clear design of chromataphores. In my talk I'll include the fascinating article by atheist JERRY FODOR (London Review of Books), protein motors in cells (Sarah Everts, C & EN), Davidson & Erwin's Science article (v. 311) - jerry coyne does a really bad job trying to refute it - and Suzan Mazur's article: www.scoop.co.nz/stories/HL0803/S00051.htm
It's never been a good time to be a darwinist, but the noose really tightens with these articles by those who have no theological axe to grind.

It's never been a good time to be a darwinist, but the noose really tightens with these articles by those who have no theological axe to grind.

<*:eyeroll:*>

Because of course someone who starts out with the premise that cephalopod chromatophores could not possibly have evolved naturally has no theological axe to grind.

Pfeh.

By Owlmirror (not verified) on 13 Mar 2008 #permalink

all the cool adaptations got taken by other species

Yes, and I noticed that cuttlefish is also awash in redundancy. Not only multiple arms and suckers, but according to the anatomy lesson three hearts, two of which serves the gills. (shakes head)

DaveX:

Light can be polarized, which can be used by animals for orientation.

gg covered the physics in a better way already, but since I composed this answer it may contribute:

Polarization is a description of the perpendicular oscillation of a general transversal wave. A longitudinal wave (oscillates in the direction of travel) such as sound has no polarization.

The wave picture of light is complicated by that EM waves have two components, E and M fields. But they are coupled (perpendicularly, btw) so a polarization description is still possible. (In the QM picture as one can surmise the spin of the photon is coupled to the polarization.)

To make a long story short, normal light sources are non-oriented so we observe equal polarization in all directions, circular polarization. But reflections (such as against water surfaces) or scattering (such as in clouds) change that, and we observe oriented elliptical polarization.

One use is that animals such as ants and bees seems to be able to orient themselves from observing the sky even on cloudy days. By using polarizers we can do the same, see the link to Haidinger's brush above, or look up the somewhat controversial Viking sunstone in Wikipedia. Another use is that polarization glasses cuts down the glare of reflections.

Btw, http://en.wikipedia.org/wiki/Polarization seems to be a good resource covering all of this, the description of the basic plane wave, et cetera.

gg:

our eyes haven't evolved polarization detection ability

Well, see the link to Haidinger's brush. But the poor detection some (most?) people may have seems to be incidental (attributed to dichroism of pigments in our oriented organelles it seems), that is for sure.

By Torbjörn Larsson, OM (not verified) on 06 Jun 2007 #permalink

A little nitpick of your comment: normal light sources are unpolarized which is different from circular polarization.

D'oh! You are right of course.

Actually, I think I have conflated these two for a very long time, so I run right into that one without thinking too much. I should have taken my own advice and refreshed the basic plane wave. :-o

Slightly embarrassing actually - I was a course assistant (in the lab) for an optics course a while. (I was rather good at it, so I had to take the darnedest slots at short notice.) But OTOH it is good to get one less confusion to drag around. Thanks!

Hmm. I don't know where to get a phone cord any longer, but I would probably benefit from pulling out a wire and start playing. Seems the simplest analogies are really the best. (Feynman knew this, I'm sure.)

which comes from the random nature of the atoms which produce the light (sometimes the atoms `feel' like radiating up/down, sometimes they `feel' like radiating left/right)

Yes, atom or molecular electron (EM emitting) orbitals has some spherical symmetries, even if not equally probable to emit radiation in every spatial angle.

But also important is that in most emitter materials the shell directions average out as well. By polycrystallinity or by being gases for example.

By Torbjörn Larsson, OM (not verified) on 06 Jun 2007 #permalink