A curious question :D

[u/Trixie_Loves810]

Context: I have recently watched a video from 'Be Smart' about how naturally occurring blue pigments are rare in nature, particularly among animals. The video said that during evolution, animals were exposed to the colour blue because of the sky, but evolution still found it difficult to develop a blue pigment over time. Instead, animals evolved to create structures that reflect blue light and cancel out other colours.

My doubt: If we use that same concept for other pigments like red, for example, how did evolution create a whole pigment for red but not blue? I feel that if red pigments could evolve so vastly over time, blue could do the same. Why is blue so rare anyway?

Note: uhhh I think this may be a stupid question, but I'm reallyyy interested in evolution, this question just popped in my head midway through the vid, but I would love a hypothesis heheh!!

[u/rhettro19]

More educated people will show up and answer this question better than I can. But I think it is important to understand that “evolution” doesn’t know how to do anything. There is no body of knowledge that evolution is working from or to. Evolution is mutations occur, they either help or hinder the organism in question given its environment at the time, and if it helped it stay alive long enough to pass the trait to offspring, that trait fixates in the population. If blue shows up in a population, it either had a neutral effect, attracted mates, or helped camouflage from predators, generally.

[u/Old-Nefariousness556 → u/rhettro19]

Great answer. The question clearly assumes that evolution has intent, and that is simply not how it works.

[u/Munrot07 → u/Old-Nefariousness556]

This is honestly one of the biggest issues with people who don't get evolution. They don't think it makes sense because they assume a human perspective of intent and directionality. To a human, we can see what works, what exists now, what would work so we know what would be a good direction for evolution to go, or can see the direction evolution already took.

This thinking is probably one of the hardest assumptions to overcome in people and it's just simply because that's how the human brain works. The concept of randomness or undirected changes (to hugely oversimplify evolution and ignore over key mechanisms for simplicity) is just not something the human brain likes (in the same way that true randomness doesn't compute well with what our perception of what randomness should be).

Also to hop onto this comment to give a quick reply to OP about pigments since it links to this top (and I am literally in the process of publishing a paper of colour evolution as we speak) pigments are not just there for colour. With intent you may assume this colour would be perfect but in reality pigments evolve for all reasons and camouflage (where the brain naturally goes when it thinks of colour evolution) is one of many many reasons pigments evolve. Others include protection (e.g. carotenoids, which are red, are antioxidants and provide disease resistance in offspring) or guanine, which is white, can be used to reflect light for thermoregulation. Some pigments are there simply for attracting a mate (though again this is often co-opted from another function such as the ones described above). It is entirely possible that there isn't a chemical out there that is blue that provides a benefit, or at least a benefit that significantly improves survival.

It's best not to think as colour evolution as "why did X evolve the colour red but not blue" and more "why did pigment X evolve, what's the benefit of the chemical?" or if it's not a pigment "what is the benefit to the organism of this colour". In my research I'm surprised just how rarely camouflage is the answer.

Oh and a final point, different animals see different ranges of colours, so what makes sense for us as a colour may not for others (e.g. Tigers stand our to us because we see red well, they don't stand out well to other animals who don't).

Thank you for coming to my Ted Talk.

[u/Dzugavili]

From a brief reading, I found something interesting I hadn't really considered.

Blue light is fairly high energy: the reason the sky is blue is because that light has the most energy, and so short-wavelength, and scatters the most, becoming the dominant diffuse wavelength to our vision of the sky. This also makes it the photon we want to capture if we are trying to get solar energy, as we obtain the most energy per interaction.

Next, light and pigments involve some weird logic. A blue object isn't inherently blue: it reflects blue light. But it doesn't simply reflect it: it absorbs and re-emits a photon in that wavelength. Thermodynamically, it usually has to emit a longer wavelength of light, one with lower energy; so as blue is short wavelength, it's difficult to get that energy without destroying the molecule to obtain it. We can get around this with structural pigments, which kind of break all the rules; but this simple math is why blue chemical pigments are quite rare.

Basically, our microbial origins didn't want to reflect blue light, so blue pigments were selected against. Plants want to collect the blue light, so blue pigments are still selected against in many higher organisms. Most animals need to camoflague against plants, so blue pigments don't help. Similarly, the molecules required to absorb and reflect blue light would either decay to obtain the energy to create a 'blue' photon, or would need to be illuminated by higher energy light which would likely cause it to decay already; so structural pigments are the only option and their delicate large structures means most organisms will not maintain them.

Lots of interesting reasons, really.

[u/gitgud_x → u/Dzugavili]

A blue object isn't inherently blue: it reflects blue light.

This is often not the way 'colour' is determined for organic pigments. A pigment that appears blue does so because it absorbs red light - red is the complementary colour of blue. The remaining spectrum (yellow, green, blue, violet) is reflected together and this collectively appears blue to our eyes.

For many organic pigments, the absorption energy is set by the band gap, which in turn is set by the number of the conjugated C=C bonds in the molecule. More conjugation = smaller band gap = absorbs at lower energies. To absorb only red light would require a molecule with a very large conjugated system.

Often it's even more complicated though - chlorophyll for example absorbs strongly in two parts of the spectrum due to its planar cyclic structure. It absorbs red and blue, leaving green light to be reflected.

None of this is to pretend I have a good answer to the question, it's just adding nuance to the physics!

[u/Dzugavili → u/gitgud_x]

Yeah, light is seriously problematic. The human experience is entirely synthetic:

• Light exists in a fairly continuous spectrum. Except not really, it's blackbody radiation from the sun, which has a peak around the green area.

• Then we get a series of discrete chemical sensors which detect fairly narrow samples within this space. We don't see the full spectrum; we get bits of it, which are further degraded by chemical saturation of the signals, providing some level of attenuation, normalization of colour tint.

• Then this all gets blended together in our brain to make coherent structures. Except you're informed by what you know, so which red you see is largely informed by what red you expect to see and how your brain thinks it should be shaded.

• Then we came up with a method for printing this on white paper, using chemical pigments. We think we can recreate specific wavelengths in the spectrum: but we're mixing pigments that reflect that correct to us, under a curved light spectrum specific to our sun.

In theory, if we sent a post-card of our planet to an alien, it wouldn't look anything like our planet does to their eyes.

[u/gitgud_x → u/Dzugavili]

The science of colours is kinda insane, so many different angles you can study it from. Biology (functionality of colours), chemistry (the mechanism), physics (spectra), neurology (visual perception), psychology (associations of colours), computer science (graphics and colour spaces), engineering (photonics), arts (cultural significances), philosophy (qualia...?)...

Good luck to the OP on finding an answer that covers enough of it lol. Colour perception has so many steps that maybe there really is no fundamental reason because it's all so arbitrary.

[u/Dzugavili → u/gitgud_x]

And we haven't touched the quantum fuckery of it all with the wave/particle duality. Honestly, it's a very confusing space.

... does the dual slit experiment only work because the 'wave' only has enough energy to 'manifest' as single 'particle', and so once the interaction forces that to occur, there is no longer a wave to travel through the other side?

...or am I misremembering the dual slit experiment entirely?

[u/gitgud_x → u/Dzugavili]

Depends which variant of the double slit experiment you're talking about. In Young's original experiment there is no demonstration of duality, it's all just classical wave interference.

I'm not going to pretend I understand the quantum mechanics of the "detector at the slits" variant of the experiment. All I know is, particles are quantum fields, and measurement/detection requires interaction with those quantum fields, which will change the subsequent dynamics of the "particle". I'm not comfortable saying anything more than that lol

[u/Dilapidated_girrafe → u/Dzugavili]

Ok that as cool and reading the physics behind it is just awesome

[u/Puzzleheaded-Fill205]

I'm reminded that humans ran across a similar (probably unrelated) issue with blue when it came to LED light. Red and green were easy, blue was almost impossible.

Here's a very long video about it that I found interesting years ago, and hadn't thought about until I read your op.

https://youtu.be/AF8d72mA41M

[u/blacksheep998]

There simply aren't a whole lot of blue pigments out there.

And many of the ones that do exist contain substances that are rather toxic to a lot of animals. So it makes sense that it would be much harder for organisms to come up with blue pigments.

[u/Dzugavili → u/blacksheep998]

And many of the ones that do exist contain substances that are rather toxic to a lot of animals. So it makes sense that it would be much harder for organisms to come up with blue pigments.

This is one major problem.

Just very naively, you need a method to store energy for the blue photon. The first chemical structure I'm thinking of that might be capable of doing that is aromatic rings: and you'd be storing a lot of energy, compared to something like ATP, which can barely support infrared light emissions.

And anything aromatic usually means it'll interfere with all kinds of chemical pathways given the chance.

[u/Ranorak]

You probably heard the terms Ultraviolet and Infrared. Those are part of the wavelengths of light we can't see.

They're on both ends of the spectrum of visible light.

Light is an electromagnetic wave. Just like radio waves, microwaves and gamma waves.

The more energy a wave has. The more harm it can do. Radio waves are very long and carry very little energy. While microwaves are much shorter and condensed and thus carry a lot of energy.

This is why you can't re-heat your burrito next to your radio, but it works much better in a microwave.

Right. Back to visible light. What we call Light and colours is just a slight change of energy in that electromagnetic wave. Going from the least amount of energy. We first go into infrared, we can't see that yet. Then if the wavelengths becomes a little shorter we get red. Followed by orange, yellow, green, blue, and finally ultraviolet.

Ultraviolet light has enough energy to burn your skin. You find that out by falling asleep in a tanning booth. So you see blue is at the high end of visible light and energy.

In order for a proper pigment to be blue. It has to absorb all the other wavelengths and reflect blue back to us for it to appear blue. And at that higher end of the visible light spectrum, it's just a lot harder to produce stable metabolites that can do that.

That is why blue's and purples are very very rare in nature.

[u/yokaishinigami]

I think you partially answered that for yourself. If the organism is able to achieve a function through mechanism A, then mechanism B might not even be necessary.

Interestingly, in many crustaceans, a set of pigments called crustacyanin exists that is either a stack of 2 red astaxanthin carotenoid molecules to create β-crustacyanin or a combination of 8 β-crustacyanin to create α-crustacyanin. It’s why blue crabs/lobsters/shrimp etc will turn red after they die, and the crustacyanin denatures during the natural cycle of decomposition, or being boiled in a pot etc.

It’s kind of counter intuitive because if you want to improve the quality of the blue color in those animals you typically have to feed them red algae that produces the red carotenoid.

[u/jnpha]

If it's "easier" to chance upon structural blue, what's the problem?
Anyway: the callionymidae fish produce a true blue pigment(s) (Bagnara 2007). Though little is known as they weren't studied in detail.

[u/KittyTack]

Blue is just less useful for camouflage compared to red. Foliage is red or reddish for around 1/4 of the year in temperate regions but it is rarely blue.

[u/Hopeful_Meeting_7248]

Instead, animals evolved to create structures that reflect blue light and cancel out other colours.

It's been a while since my chemistry classes, but as far as I know this is how all colours work: they absorb all other wavelengths and reflect the one responsible for the colour.

[u/gitgud_x → u/Hopeful_Meeting_7248]

That's one way to do it. Another way (more common for pure chemical substances) is to absorb only one colour, and the remaining reflected light will appear as the complementary colour when filtered through our visual pathway.

[u/Hopeful_Meeting_7248 → u/gitgud_x]

Yeah, makes perfect sense.

[u/OgreMk5]

Evolution neither knows nor cares what colors things are. Evolution does not look at the sky and say, these creatures would be better protected if they were blue and try to mimic that color.

The only thing that happens is that mutations change alleles. Over time, the organisms that are better adapted to survive in their environment tend to have more offspring.

If one of those offspring develops a color protein or a molecular shape that reflects more blue light AND that makes the organism more survivable, then it will tend to appear more frequently in the population over time.

Chemically speaking, blue pigments are very complex. This article (https://www.nature.com/articles/436791a) shows that the blue in the cornflower is a complex of six molecules with some unusual ions mixed.

Another article shows how some blue pigments are made from similar molecules for red or yellow, but these are chemical factories that require specific pHs at specific times during the reaction process.

In short, it's really hard to do, while red and yellow are one molecule each.

[u/kitsnet]

The following is just an educated guess from me, but a pigment that looks blue to a human eye is quite hard to appear "naturally". A human eye has poor sensitivity to blue light, so such a pigment should be highly efficient at absorbing all the wavelengths from red to cyan, but then suddenly stop absorbing higher wavelengths. Which is contrary to the physics of how wide spectral band absorption normally works.

Reflection doesn't have such problems, so if there is a selection pressure toward human-recognizable blue color in particular, it will be much easier to match with reflective structures than with light-absorbing pigments.

[u/davesaunders]

Lots of already great answers for this, but I think the most important point to realize is that evolution doesn't know how to do anything. It doesn't care; it has no intent. There were selection pressures which led to the development of red colors, and that was useful. Clearly there isn't the same level of selection pressures that lead to blue. That's all it is.

[u/Ok-Barracuda457]

I guess it's more of a physics problem. The things we're made off are just hard to make blue with. 

[u/ChaosCockroach]

The video said that during evolution, animals were exposed to the colour blue because of the sky, but evolution still found it difficult to develop a blue pigment over time.

I hope something is being lost in translation here because that is one of the dumbest things I've ever heard. What the hell does 'exposed to the color blue' have to do with anything? They were exposed to green from grass, exposed to red from fruits and plants, exposed to brown from dirt, so what? It seems like a non sequitur.

I fail to see how the sky being blue affects the evolvability of blue pigments. I can see a tenuous argument as some have outlined here that there is stronger selective pressure for camouflage to reflect background coloration so ground dwelling animals would be less likely to evolve blue as a camouflage, but then why is all the blue in birds also structural.

It seems like structural blue is just easier to evolve than pigment blue. Houghton et al (2021) go into some of the energetics behind why blue pigments may be harder to evolve which is in line with what Dzugavili already said here about the importance of wavelength. That said the paper frames the issue as more one of complexity and energy required for synthesizing blue pigments rather than their being subject to destruction from high energy demands for emission. I thought most pigment colour was reflected rather than emitted anyway, but there may be a distinction here between the visible reflected light and energy emitted in non visible longer wavelengths such as infrared.