I just saw another vid about how rare the color blue is in nature, but

Factual Questions
1

they don’t seem to ever mention blue eggs.

Over the years I’ve read several articles about how rare and hard it is for plants and animals to create the color blue (Here’s one for example https://www.livescience.com/why-blue-rare-in-nature.html.) and just today I saw it referenced in another youtube vid. According to it, less than ten percent of flower species are blue, and blue animals are even rarer. Apparently mostly the color depends on tricks such as diffracting light in various ways rather than some substance that actually looks blue on its own.

But I don’t think these articles ever mention egg shells. I bet everyone has seen a discarded robin’s egg, which are as blue as you could ask for. There are hens that lay blue eggs, too – I’ve eaten some in fact.

So how are they blue? Another diffraction trick?

2

The blue of egg shells is from a chemical called oocyanin, which is extremely similar to biliverdin which makes bile green. Green eggs are colored by biliverdin. Brown eggs are colored by bilirubin. Seems generally egg pigments are bile pigments.

3

Okaaay… but, um, how it be simultaneously true that ‘it’s hard for living things to create blue substances’ and ‘hens just tweak unlimited amounts of blue from their own bile every day?’

4

The difference is that it’s not a pigment that ends up in skin or fur or feathers or scales.

5

Where is the blue food? Who has all the blue food?

-George Carlin

6

This is why sticky plasters in catering establishment first aid kits are always blue.

7

As I understand it, biliverdin can end up in the fur of some newborn animals, but it’s from in utero uptake and will fade. There’s probably just no easy pathway for it or other bile pigments to end up in pigment cells, which produce their own pigments, whereas bile pigments are produced elsewhere. In the case of egg shells, specifically by the shell gland and oviduct.

There are some animals that do produce their own blue pigments, rather than diffraction tricks, though as you can tell by the refrain of “unknown chemical structure” and “undefined pigments”, this isn’t a well-studied area.

8

The mandrill is a fairly close relative to humanity, and uses a blue pigment in its skin.

I suspect that this means that mandrills are, like humans, capable of perceiving the colour blue, unlike most mammals.

There is little point in utilising a colour that the animal concerned can’t see.

9

Looks like it’s a structural color:
https://www.science.org/content/article/whats-behind-blue-behind

10

That makes sense, but my point stands. Several birds have blue feathers or other parts, generally caused by tiny components that diffract sunlight; but there is no point evolving such features unless the species concerned are capable of perceiving blue colours.

11

Most mammals see violet to greenish-yellow. It’s red that they lack.

Actually a human with red-green color blindness has a similar color gamut to a typical mammal.

12

Yeah, but why? I’m probably not expressing this at all well, let me try again: robins, for example, grab hydrogen and carbon and whatever molecules from what they breathe, eat and drink, right? And then some of their cells hook them together according to the instructions in the DNA to make this or that substance that looks blue.

The fact that they do it all, means they can do it.

It doesn’t take some exotic element or chemical rarely found in the environment, whatever it needs must be relatively plentiful in bugs and water and air and seeds, yes?

And it can’t really require anything beyond the usual (amazing) chemistry of life: take one molecule, use some protein or whatever to chop off THAT group of molecules, paste them onto this other group of molecules you’re stealing from a pine nut or whatever, presto-chango you now have a molecule of oocyanin, or whatever it was.

So if the the necessary substances are at hand, and the chemical instructions for building the desired pigment are in every damn cell of the chicken, why hasn’t some mutant chicken been born with the feather cells pumping out that blue dye?

Assuming getting colored is a good thing evolutionarily, and it must potentially be given that we DO have a world full of green and red and yellow things, what’s holding up the bright blue tomatoes?

13

I understand your question, but I don’t know that there exists an answer for it. Blue coloring is clearly useful, because birds, fish, and reptiles all make use of it sometimes, through structural means. For example, blue fish scales use a black pigment with reflective structures above it to get a blue color. And yes, birds with blue eggs are capable of producing a blue pigment. But for whatever reason, evolution has never selected for that pigment to appear in skin, hair, feathers, etc.

It’s possible that this is due to some side effect inherent to this pigment that makes it undesirable. It’s also possible that it’s just never come up because evolution takes the path of least resistance and if you’ve already got a black pigment present in your scales it’s easier to evolve structural elements that make you appear blue than it is to bring a totally new pigment in to those scales.

14

They’re not switched on though.

It takes more than one mutation to switch that on - the cell also needs to be supplied with the right raw materials for it - liver and egg gland cells are, and skin cells aren’t. No single random mutation is going to change a whole system like that.

15

Interesting. I wonder which of these simulations is closest to a typical mammalian perception of colour.
https://www.color-blindness.com/coblis-color-blindness-simulator/
Some of them display the blue pigments clearly, while others barely show them at all.

And as some contributors have noted, the occurrence of blue colours in nature are very often the result of physical structures rather than pigments. Most birds with blue feathers are that colour because of tiny diffracting grids in their feathers; and the blue of a mandrill’s snout is also a diffraction effect, it seems. So you don’t need to evolve a blue pigment, so long as you’ve got tiny striations in your outer covering.

16

It could be that when life emerged it locked itself into certain chemical pathways that did not easily accommodate blue. Maybe switching between “Blue” chemical paths and the current path requires too many steps for a single mutation or simple chemical switch to allow blue pigments to be included in our biology. So once the system has set up, there might be little biochemical ability to include blue. So non-chemical processes take the lead for displaying blue.

All this is pure speculation, of course.

17

The answer might lie in simple probability and chance. The has to be some color that appears less often than the others (unless they all appear equally often, which is also pretty unlikely).

We’d like to find some reason for the distribution curve, but sometimes there isn’t any.

You might want to find a statistics expert, and ask, “Given these particular colors, how often should I expect to see the distribution skewed this much?” But for them to calculate your answer, you’re going to have to give them a specific list of colors, and the distribution that you’ve observed. (And probably other stuff that this amateur can’t imagine.) But just those two questions are trouble enough. Do you have only two colors, called Blue and Not-blue? Or the three primaries? Do teal and aquamarine cout as blue or as green? And what objects are you looking at: Only animals? Animals and plants? Animals and plant and rocks? Animals and plants and rocks and oceans and skies? When doing the calculations, do all the mandrills count as one, or do we need a population survey? How many do the oceans count as?

I hope you get my point. Good luck!!

18

Basically, this is the extension of adaptive landscape concept as illustrated in Dawkins’ Climbing Mount Improbable. - that there are local minima and maxima of “fitness” that mean once you go down one pathway, others are excluded, or at least made very, very difficult.

19

The question is perhaps more about why the colour humans and other tristimulus colour seeing animals perceive as blue is less common.

There is only evolutionary pressure to make blue when interaction with animals that can see it matters. Animals that can’t see into the red will be just as happy with purples as blue. Plants do flowers of violet happily. The street where I am sitting is lined with Jacarandas in full bloom right now. Need see into the near UV, so what works for them can be invisible to us. Overall there is probably no reason for any plant to put effort into adsorbing red whilst reflecting blue.

Otherwise plants just use chlorophyll and chemistry demands that that is green for best efficiency with a minority still using reds. That was worked out long before anything that could perceive colour existed.

For mammals hair colour seems to be based on pretty much just melanin, in the form of eumelanin and pheomelanin. In dilute form you get yellows, and then dark yellows aka brown, and eventually black, or blondes to red hair. Furred animals have a well developed mechanism for creating a wide variety of patterning that is based on only varying concentration of one thing - melanin. So a big barrier to developing a patterning system that has additional colours.

Pigments that are stable seem to be harder for blues. Flowers don’t have a problem with this as they only last a short time. Animal markings would not work if they faded after a few weeks of sun.

Overall I suspect the answer lies in a mix of bias from our particular colour perception capability, a lack of evolutionary pressure, and the likely difficulty of making stable blues. So blues are relegated to diffraction effects.

Using diffraction allows for a vastly wider and vivid palate of colours anyway. So you may also say that diffraction has overtaken pigments as the best mechanism for colours, leaving us drab melanin tinted creatures as nature’s fashion losers.

20

well , with all this discussion of the haemoglobin family of organic molecules , there are two other families to add in . Chlorophyll , which is green, and carotenes, which are orange.

Another set of colours are found in the petals of flowers,which are often pH indicators. Now the plant can have parts with varying pH , but the animal with the need for oxygen supply to all living cells, also ensured the pH variation thing can’t be used.

How do these pigments turn white light into their colour of light ?
green ? absorb signficant parts of the red and blue spectrum.
orange ? absorb signficant blue spectrum
red ? absorb signficant blue and green .

blue ? absorb significant red and green .

Now, energy of a photon = hf . that is, energy is proportional to frequency.
So to absorb red AND green but not blue, you need lots and lots of smaller molecules or active sites that are SMALLER. There are just less organic chemical forumations to allow that,because there’s less options when making smaller sites.

For example ,chlorophyl has a “metal” atom embedded in its molecule. Something that in pure form would be like iron or tin. there’s a few different metals in versions of chlorophyll, … the options are limitted. Haemoglobin, hey thats got a metal there, iron, and well the animal is going to need the Haemoglobin right ? Haemoglobin would have evolved as a store of oxygen, for surviving through times of low oxygen. Before evolving into blood, to ensure the flow of oyxgen through the tissue.

Curiously one simple (small) organic pigment for blue is cyanide, but heck thats got rather drastic consequences if your cells just decide to start making that. Its deleted from the gene pool as soon as it evolved there ? (You can have safe cyanide in larger molecules, but the evolutionary path for that has to exist. )

Well anyway, it seems to me that deleting a wide range of red and green parts of the spectrum but not much of the blue part is rare, because of the way electrons can absorb a minimum energy photon, or a scattering of higher energies… when considering the isolated atom. Blue having higher energy, its in the scattering . creating the situation , via crystal or molecular structure, of the electrons being limited to absorbing lots of energies in those scatterings, but not in the higher energy blue, thats hard…which means relatively less likely than subtances that are not-blue.

counter-point… brown ? the scattering … brown things absorbs visual frequencies X Y and Z … a few, of varying frequencies, no perfection required. Blue is a perfect absorption behavior, the substance has to be so perfect at absorbing red and green, and yet not have the scattering of absorption lines in blue.