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Nature is full of all kinds of beautiful color, and there is plenty of weird science there too! Here's a showcase of a few of our episodes all about coloration.

Hosted by: Hank Green

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Original Episodes:
3 of the World’s Most Intensely-Colored Living Things
https://www.youtube.com/watch?v=XCphJi03_0A

Why Aren’t Mammals More Colorful?
https://www.youtube.com/watch?v=pyhULLXLUDw

The Horrible Reason Rollie Pollies Are Sometimes Blue
https://www.youtube.com/watch?v=8q7jswQHM_Q

The Unique Reason Reindeer Change Their Eye Color
https://www.youtube.com/watch?v=zzeMkfViSYY

The Delightful Mutation Behind Siamese Cats
https://www.youtube.com/watch?v=uHC1XTF6b58

 Introduction


There are some amazing plants and animals out there. You got giant ones, tiny ones, cute ones, really weird looking ones and everything in between. (0:17)  Like, whatever strange characteristic you're looking for, I am sure there is a creature for you. But one key feature we tend to notice about plant and animals is their color. (0:27)  There is plenty of weird science there, too. We've done a handful of episodes about coloration over the years but we wanted to showcase them finally all in one place together.  So kick back, relax and get ready to be amazed. (0:41)  Lets start with the superlatives.  While there are all sorts of lovely colors out there, some species have gone above and beyond.

And they are officially considered the worlds most intensely colored things. (0:56)  I want to turn it over to Stephen for the details. (0:58)

 3 of the world's most intensely-colored living things


The world is filled with an abundance of colors. Now, some stand out more than others with super shimmery blues, whiter than white whites or darker than dark blacks. (1:10) Today we are going to talk about three of the most intensely colored living things. What's really fascinating about these three is their signature looks are all made without colorful molecules. (1:19) The color you see when you look at an object or a living thing is determined by the wavelengths of light it reflects back into your eyes. White light, like the light from the sun, contains all the wavelengths we perceive as colors.

When it hits something, that thing absorbs some wavelengths of light and reflects others. (1:33) For most living things, what's reflected is determined by pigments: "Colorful" chemical compounds that absorb certain wavelengths of light. Leaves are green, for instance, because they contain chlorophylls. Pigments that largely absorb all light except for green wavelengths. (1:46) And that is all well and good for most colors, but the most intense colors we see in nature don't tend to come from pigments.

They come from a phenomenon called structural coloration. That's when the light reflected or absorbed depends on microscopic structure of a surface and not the absorption properties of specific molecules. (2:03)

 (02:00) to (04:00)


Take the marble berry for instance. (2:05)
It's the vivid fruit of an African urbatious plant  and back in 2012 it was heralded as the most intense natural color on the planet. (2:11)
And it's not hard to see why. These small berries which are smaller than Blueberrries hack a colorful punch. Their bright iridescent surfaces sparkle and shine in stunning blues and purples. But unlike other berries Marble berries don't get their colors from pigments, instead it comes from unique structures in the outer layer of the fruit. (2:29)
The outermost layer, called the cuticle, is glossy and transparent. Allowing light reflected from the tissue below - the epicarp - to shine through. (2:37)
The cells in the tissue contains translucent cellulose microfibers stacked in miniature spirals. These microfibers act like a series of mirrors, reflecting the light back and forth between them. (2:46)
Depending on the thickness and direction of the spiral as well as the thickness of the cell's wall, each cell reflects red, green or blue wavelengths. Though most of them reflect blue light, causing the berry to have a somewhat speckled but generally blue appearance. (2:59)
Below these cells is a layer of dense brown tannin pigments followed by a third layer, an even deeper sheet of thin cells. Tannins absorb most of the light that gets to them, while the thin cells scatter what's left to enhance the purity of the color produced by the spirals. In total the berries reflect 30% of the light that hits them. (3:16)
And as for why the berries are such a brilliant blue. Well that's likely to attract berry-lovers like birds. In general plants that make berries are hoping animals will eat them. Because that means birds they'll carry their seeds in their guts for a while before depositing them in a hopefully distant location. (3:29)
Bur marble berries don't contain lots of jummy flesh. So animals have no particular reason to help the plants to disperse their seeds. Except of course that the berries are so shiny and blue. It's thought that the coloration either fools birds into thinking they are different, more nutritious species or simply looks amazing. (3:44)
See, during courtship lots of bird-species decorate their nests or others structures to proof they're a high-quality mate. So a shiny blue berry could bring their mating display to the next level. (3:55)
Either way the berries get dragged around helping the plant reach new areas.

 (04:00) to (06:00)


Now while the berries 30% reflectance is impressive, it's nothing compared to the brilliant 70 plus percent reflectance of the Southeast-Asian Cypnochilus Beetle. (4:08)
Their whiteness is so bright that it almost hurts to look at them. And they get this super-whiteness from their unique scales. Each is comprised of numerous tiny filaments densely packed together. These fibrils are really good at scattering light and because the scattering is random all wavelengths are scattered equally making them result in the color white. (4:25)
Which is all well and good for the beetles because it lets them blend in with the white funghi that they like to live on. White are also useful to us of course, which is why researchers have created an artificial white substance that mimics the structure of cyonchilus scale. (4:37)
This substance is 20 to 30 times more white than normal white filter paper and retains this clarity of color down to a mere 10 microns thick. That's thinner than a human hair. (4:48)
Now on the other hand creating the blackest black required the exact opposite approach. Black is the absence of all color. So to make deep, dark black you need to make something that absorbs most if not all of the wavelengths beaming at it. And that's exactly what the feathers of several birds of paradise do. Some people who have seen these birds up close say looking at their feathers is like looking into a dark void. And that's actually a pretty abt comparison because the birds feathers reflect a mere 0.05& to 0.31% of the light that hits them. (5:11)
Compare that to normal black bird feathers, which reflect about 3 to 5%. The difference in blackness comes from modifications to small branched of the feathers called the barbules. 
In most birds these are relatively flat and thin. All the absorption is done by dark pigments inside the feather. But in the black feathers from birds of paradise the barbules are curved, dense and packed with tiny spikes. These reflect any escaping light back inwards towards the bird, trapping it in the feathers until its absorbed. And you might think something that deep and dark was trying to hide but that's not what these birds are after. (5:46)
Instead it's thought that their super-black feathers helps them highlight the colors of the rest of their plumage (?~5:51) which they use during courtship to whoo a mate. Which is why nothing but the blackest black would do. (5:55)
Though there are lots of ways to make beautiful colors, it seems like when nature wants something really intense light absorbing compounds just don't cut it. (6:04)

 (06:00) to (08:00)


Those feathers are outrageously dark and plenty of other birds have amazing supersaturated coloration too. Just look at a parrot or like half the birds you'd find in a rainforest. In fact lots of animals come in a rainbow of colors except for one particularly significant group: mammals. We come in only a few more neutral colors. (6:27)
So why did us mammals miss out on all the fun. Here's one from Olivia. 

 Why aren't mammals more colorful?


Nature is full of color. Birds, beetles, fish, flowers and more come in every color of the rainbow but mammals not so much. (6:43
We and our fuzzy relatives don't tend to have the vivid colors of other animals. Think of a tiger or a calico cat. Most of the time that's about as vibrant as it gets. 
The evolutionary reason for mammals subdued coloration is more complex than you might think. And it takes us all the way to the age of dinosaurs. (7:00)
Most of the colors you see in plants and animals come from molecules called pigments, which absorb certain wavelengths of light and reflect back others. These are stored in their skin, feathers, fur or scales to produce all kinds of bright reds, pinks, yellows and more. Us mammals tend to be less colorful than say birds, lizards or insects. In part because we don't have the same range of pigments they do. (7:20)
Most mammals can only make category of pigments called melanin. Melanin comes in two forms: eumelanin, which can produce black or brown coloration and pheomelanin, which produces yellow or reddish-brown colors. Different amounts of melanin in different parts of the body can create a variety of patterns from the black and whits stripes of zebras to the brownish and yellowish spots of giraffes. (7:40)
As for other pigments we don't really have the genes to make them. But mammals can be more colorful. Mandrils are a type of monkeys that exhibit striking blue and red coloration of their faces and also around their genitals. (7:52)
The red comes from blood vessels showing through the skin and the blue is a result of structural coloration, in which the skin scatters and reflects light in such a way that blue wavelengths are directed back at your eyes. (8:02)

 (08:00) to (10:00)


In fact most blues you see in animals are structural colors and lots of animals don't even make their pigments themselves. Flamingos for example, pick up their pink from their diet and there doen't seem to be any specific reason mammals haven't evolved to do something similar. (8:16)
Which leads to a conundrum of sorts. We know mammals have the capacity to be more colorful but they usually aren't. So, why not?´The most likely explanation is that mandrills, birds and butterflies all share an ability that most mammals don't have: they have excellent color vision. (8:31)
You see, inside your eyes are specialized cells called cone cells, which grant you the power of color-vision. Many fish, reptiles and birds have four types of cone cells each with light receptors tuned to a different wavelength of light. (8:45)
Seeing all these different wavelengths together creates a complex multicolored picture. But most mammals only have two types of cones, making them dichromatic. And since their cone cells can only pick up two main wavelengths of light they miss out on a lot of color information. (9:00)
Usually, these cones are tuned to the green and blue end of the spectrum leaving them less able to clearly discern reds and yellows. In human terms they are partially colorblind. Primates are an exception to this. Most primates, including ourselves, are trichromatic with three types of cones for seeing reds, greens and blues. Since primates can see a variety of colors it makes much more sense for them to use bright colors for communication. There is less point in flashing fancy colors if others members of your species can't see them. (9:27)
Even with our fancy third set of cones, though our color-vision isn't as good as many of the non-mammals in the world. If you're feeling a bit cheated, try blaming the dinosaurs. During the mesozoic era, roughly 250 to 66 million years ago the world was ruled by reptiles but there were mammals too and although they were mostly small and scares compared to today. They were pretty successful in a variety of niches around the world. (9:50)
With dinosaurs dominating most lan ecosystems, mammals needed to find strategies to avoid competing with them and being nocturnal could have been a great tactic. (9:59)

 (10:00) to (12:00)


It's hypothesized that many mesozoid dinosaurs where active during the day, so only coming out at night would have been a way for early mammals to avoid either competing with them for food or becoming lunch themselves. (10:09)
This has become known as the nocturnal bottleneck hypothesis. In evolution a bottleneck occurs when a populations genetic diversity becomes reduced. In this case as a result of adapting to life in the dark. In studying the genomes of modern mammals scientist have determined that not only do we reduced vision, we also tend to be missing certain genes that protect our skin and eyes from damaging UV radiation. (10:31)
Color vision and UV protection are both really helpful if you spend a lot of time in the sun but less important if you're active at night. In this case all or most mammals are thought to have lost these daytime traits during the mesozoic. So scientist suspect our mammalian ancestors may have spend most of the mesozoic in the dark. (10:48)
Then when the dinosaurs rein ended and the mammals finally got their time in the sun they were working with limited genetic tools for adapting to daylight. Some of the genes that enabled daytime activities had been selected out and were long gone. So even though many mammals are active in the daytime now their DNA is still sort of stuck in nighttime mode. Only certain mammals like primates have separates evolved more complex color vision. (11:11)
And with it more colors on their bodies. Our mammal eyes may never be able to see colors as vivid and varied as birds eyes can see but that's a trade-off that allowed our ancestors to survive living alongside their ancestors. (11:25)
Fortunately we humans can always add a splash of colors with a favorite sweater. (11:28)

 Intermediate


Well, I guess surviving is a pretty good reason to come in boring colors. Especially when you realize that some animals come in bright colors for some kind of horrible reasons. (11:39)
Take rollie pollies or pill bugs they are usually dark grey but sometimes they come in a lovely vivid blue which sounds really nice and beautiful until you learn what causes that. (11:51)
Here's Michael with the details. 

 (12:00) to (14:00)


 The horrible reason rollie pollies are sometimes blue


You might call them wood lice, pillbugs, potatobugs or rollie pollies but they aren't lice or bugs, they aren't even insects. (12:00) They're terrestrial isopods, the only fully land-dwelling crustaceans. They come in all sorts of colors. There's brown, light-brown, black, every once in a while though you might get lucky and find a brilliant blue rollie pollie crawling around in the dirt. But you're good luck is their bad luck because that blue comes from a virus and when it makes them colorful like that the virus is almost always lethal. (12:22)
The viruses that turn rollie pollies into "rollie blueies" are part of a larger family known as iridoviruses. (12:28)
Iridoviruses can infect all sorts of ectotherms - animals whose body heat primarily comes from their environment - including crustaceans like our friends the pillbugs, true insects, reptiles, and fish. And at least among the invertebrates on that list the most obvious symptom is a noticeable color change both inside and outside the animal. (12:46)
Infected animals can turn blue, green, yellow, red, or just be kind of shimmery, depending on the virus. Now on its own that isn't too remarkable. Pleanty of illnesses change an organisms color but most infection-related color-changes come from some sort of pigment - a chemical that reflects certain colors and not others. (13:02)
Iridoviruses don't use pigments. You can't put iridoviruses in a test-tube and extract a blue substance from them. That's because the blue of infected pillbugs is an example of structural color. It's the arrangement of the viruses inside an animals cell that determines what color the cell appears to be and ultimately down to the wavelength properties of light. (13:20)
Waves can interfere with each other reinforcing or cancelling out depending on the way that crests and troughs line up with one another and that interference can alter what color is perceived. For example, red lights wavelength is around 700 nanometers. So, if you had two semi-reflective layers of something, like layers of glass, separated by about 700 nanometers the crests of the red light reflected by one would overlap with the crests reflected by the other, making it seem like the thing is tinted red, but if the layers were separated by about 350 nanometers instead the crests reflected by one would overlap with the troughs reflected by the other. (13:54)
No red light would come out at all even though both layers are reflecting red and the same goes if you have individual atoms doing the reflecting instead of layers of glass. (14:01)

 (14:00) to (16:00)



So structural color, the color you see doesn't just depend on the colors that are reflected, it depends on the physical arrangement, separation, and the physical properties of whatever is doing the reflecting. You can find structural coloring in butterfly wings, birds, beetles, and plenty of other species and you can find it in animals tinted by iridoviruses. That's because the viruses don't just spread just all over the place when they reproduce inside a host animals cells. They arrange into rows and larger structures a lot like atoms do in a crystal. (14:27)
Smaller viruses tend to pack closer together, leading to a blue tint that's seen in rollie pollies, larger viruses tend to spread out more, giving us redder animals instead. Iridoviruses have one more curve ball to throw though. Sometimes they cause this kind of characteristic color change but usually the don't. Two animals of the same species can even be infected by the same kind of iridovirus and one might change color while the other doesn't. (14:49) These are called covert infections and scientists still aren't sure what makes viruses go down one path or the other partly because they are not sure why iridoviruses color animals in the first place. (15:01)
Iridescent infections are easy for other potential hosts to avoid which could potentially make it harder for the virus to spread. However a bright bug is more likely to get eaten than one that's well camouflaged and a predator that eats an infected bug in one place could carry the infection elsewhere. (15:16)
So some scientists think that obvious colors help the viruses spread far and wide while covert infections led the viruses move around within a single population. It's also possible that the colorfulness of the viruses isn't an adaptation in itself. Patent infections - the ones that cause color changes - happen when the virus reproduces really quickly inside a host's cells, while covert infections tend to be when the virus reproduces more slowly and it could just be that when lots of viruses cram into a cell, it takes less energy to arrange like a crystal than it would to do something else. (15:45)
What we do know is that patent and covert infections tend to have different symptoms. Patent infections are just about universally lethal but they don't usually go full-on pandemic and kill whole animal communities. They just consistently infect small percentages of certain species anywhere from one in a hundred individuals to one in a million. (16:01)

 (16:00) to (18:00)



Covert infections are much more common, estimates range from ten to thousands of times as common, depending on the host species. And they're not nearly as lethal as patent infections. They usually impact things like an animals ability to move around or reproduce. Whether patent or covert though iridoviruses can have some pretty big ecological effects. THey've killed off whole populations of tiger salamanders and bass and they've been found in bee colonies that have suddenly died, suggesting they might play a role in colony collapse disorder, too. (16:28)
Understanding the epidemiology of these viruses could help researchers predict and prevent outbreaks in species we don't wanna loose, like bees. And it might even allow scientists to get the viruses to do some good, like control invasive pests. In the meantime they give physicists and biologists something to talk about at a dinner party. (16:45)

 Intermediate


Well in the end at least those viruses might be useful, it doesn't make life easier as a rollie pollie but it's a silver lining at least. Thankfully not every blue in nature means death is knocking on your doorstep, like with reindeer. (17:00)
Reindeer eyes, specifically, unless you about some species I don't. Here's another one from Olivia. (17:06)

 The unique reason reindeer change their eye color


Shine a light into the woods at night and you might see the glow of eyes staring back at you but the eyes aren't actually glowing. They're reflecting light off a special layer of tissue found in some animals called a tapetum lucidum. The color and shape of this eye shine can tell you what's peering at you from the darkness but things are more complicated if you're in the arctic regions of Norway. (17:30)
Because there reindeer change the color of that part of their eye seasonally. That's right, the animals most famous for pulling Santas slay have eyes that change color to help them see in the darkness of winter. Animals that need to see well in low light like cats, raccoons, and even reindeer all have tapetum lucidum. (17:49)
They sit in the back of the eyes, right in between the outer layer of the eye and the retina, the part that actually sees. These thin tissues act as reflectors giving retina a second change at absorbing light. (18:00)

 (18:00) to (20:00)


Most animals have a particular color of eye shine which depends on the composition and structure of their tapetun lucidum but the Eurasian mountain reindeer is different. It's the only one we know of that switches colors, changing from a summery golden yellow to a deep blue in winter. (18:14)
And scientists think that's a side effect of how their eyes have adapted to long periods of darkness. The arctic summers where they live have 24 hour days and the winters include long stretches of night. The animals compensate for this in part by making their retinas more responsive to low light in winter. (18:30
And it's believed they can see some wavelengths of UV light but that's not the most obvious adaptation. 
To see better when it's so dang dark. a reindeer's pupil open wide to let more light in, kind of like yours do if you go into a dark room, but when a pupil stretches wider it also flattens the front of the eye ever so slightly, which increases the pressure inside the eye. (18:50)
Since their pupils are constantly wide open during winter, that pressure builds up, squeezing the tiny collagen fibers from the deer's tapetum lucidum closer together. And this compression causes the color change. (19:02)
The tightly-packed fibers strongly reflect shorter, blue wavelengths of light, while the more spaced out fibers reflect longer, yellow ones instead - a phenomenon known as Bragg's Law. (19:12)
Researchers can actually compress a dissected piece of the reindeers eye with a tiny weight and induce the same yellow-blue color change but the color isn't what's really important to the animal. 
The compressed fibers also scatter light sideways through the retina instead of reflecting it out of the eye, increasing the amount of light the retina can absorb. While summer eyes reflect more than 95 percent of the light shone into them, winter eyes reflect only 40 percent. And that likely means the reindeer can see in what seems like total blackness. The only downside to this amazing feed is because light rays inside the eye are more scattered, everything also looks a little fuzzier but that seems a small prize to pay. I wish I could trade a little blurriness for night vision. (19:54)

 Intermediate


Now I feel like reindeer need like cute little reindeer glasses. (20:00)


 (20:00) to (22:00)



Speaking of cute things: Siamese cats. They have those adorable dark mittens and little brown ears and a cute little face but what gives them their distinctive look? Here's one more episode with a surprising, and my father-in-law let me know, absolutely mind-blowing answer. (20:19)
Seriously he loved this episode. 

 The delightful mutation behind siamese cats


From a tigers stripes, to a jaguars rosettes, to a tabbys warls, cats come in lots of different colors and patterns. Normally we imagine that the way an animal looks is inherited from its parents - basic genetic stuff. (20:35
But sometimes the origin isn't so simple. Like the coloring of some domestic cats is tied to their sex. That's why orange cats are much more likely to be males and calicos and tordies are almost always female. But siamese cats are especially interesting because their recognisable coloration is actually dependent on temperature. (20:58)
Animals get their dark color because their bodies produce melanin. Melanin is the same protein that is responsible for variation in human skin-tone and making you tan and its produced thanks in part to the enzyme tyrosinase. Normally this enzyme does its job pretty well but in some breeds of mouse, rabbit, and cat and even in some human cases the enzyme doesn't quite work the same. (21:22)
In particular virtually all siamese cats have a mutated version of the gene that codes for size enzyme. So their tyrosinase is extremely sensitive to temperature. So sensitive, in fact, that it unfolds and no longer functions at the average cat body temperature around 38 degrees celsius. (21:42)
That isn't great for the enzyme, can't really do its job anymore but it does give their adorable coloration. Without functional tyrosinase no melanin gets produced, so most of the animals fur is a creamy-white. It's essentially albino. (21:59)

 (22:00) to (24:00)


But siamese cats also have those super-cute boots and that little brown mask and that's because tyrosinase is functional in their extremities, like their tales, legs, noses and ears. Compared to their volume these parts of the body have a larger surface area for heat to escape from. So these small and slender body parts loose heat more quickly than the cats central core. (22:23)
That's just like how your fingers, and feet, and nose are the first things to get cold when you step outside or how a narrow icicle is gonna melt before a compact icecube made of the same volume of water. (22:35)
In a cat that means the face, limbs and tale are just a few degrees cooler compared to the rest of the animals body and that difference is enough to preserve delicate tyrosinases shape and function, allowing it to color the fur. (22:50)
If you ever get to see a newborn siamese kitten you can actually watch this process happen life. When the cats are born they're totally white since the inside of the womb is a uniform and toasty 38 degrees celsius or so. Out in the world, the temperature around the kitten is cooler than its body so it loses heat to the environment especially from its tiny toes and tail. (23:13)
Within a few weeks the characteristic siamese color pattern starts to emerge as new fur grows and tyrosinase gets to work in the cats extremities. So unless you keep mittens on your kittens siamese cats will develop their trademark coloration, all thanks to this delightful mutation. (23:31)
Cats are unsurprisingly just so great. Thank you for watching this episode of SciShow. Compilations like this make me realize how much content we have put out over the years and whe couldn't have done it without the support of our patrons on Patreon and our channel members. If you support SciShow you helping put more free educational videos out into the world to be watched by people wjo love them, to be used in classrooms all over the place and we are really grateful for that. (24:00)


 (24:00) to (24:16)



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