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  • thanks to SkillShare for supporting this episode of SciShow

  • [ intro ]

  • Nature is full of color!

  • Birds, beetles, fish, flowers, and more come in every color of the rainbow.

  • But mammals, not so much.

  • 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 back to the Age of Dinosaurs.

  • 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.

  • Most mammals can only make one 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 white stripes of zebras to the brownish and yellowish spots of giraffes.

  • As for other pigments, we don't really have the genes to make them.

  • But mammals /can/ be more colorful.

  • Mandrills are a type of monkey that exhibit striking blue and red coloration on their

  • faces

  • and also around their genitals.

  • 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 our eyes.

  • 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 doesn't really seem to be any specific reason mammals haven't evolved

  • to do something similar.

  • 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.

  • 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.

  • Seeing all these different wavelengths together creates a complex,

  • multicolored picture.

  • [DYE-kro-matt-ik] 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.

  • 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're partially color blind.

  • Primates are an exception to this.

  • Most primatesincluding ourselvesare trichromatic,

  • with three types of cones for seeing reds, greens, and blues.

  • Since primates can see a variety of colorss,

  • it makes much more sense for them to use bright colors for communication.

  • There's less point in flashing fancy colors if the other members of your species can't

  • see them.

  • 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 back then, too,

  • and although they were mostly small and scarce compared to today, they were pretty successful

  • in a variety of niches around the world.

  • With dinosaurs dominating most land ecosystems, mammals needed to find strategies to avoid

  • competing with them.

  • And being nocturnal could have been a great tactic.

  • It's hypothesized that many Mesozoic dinosaurs were 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.

  • This has become known as the nocturnal bottleneck hypothesis.

  • In evolution, a bottleneck occurs when a population's genetic diversity becomes reduced --

  • in this case, as a result of adapting to life in the dark.

  • In studying the genomes of modern mammals,

  • scientists have determined that not only do we have reduced vision,

  • we also tend to be missing certain genes that protect our skin and eyes from damaging UV

  • radiation.

  • 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 scientists suspect our mammalian ancestors may have spent most of the Mesozoic in the

  • dark.

  • Then, when the dinosaurs' reign ended, and 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 mammalslike primates

  • have separately evolved more complex color vision, 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 the trade-off that allowed /our/r ancestors to survive living alongside /their/

  • ancestors.

  • Fortunately, we humans can always add a splash of color with a favorite sweater.

  • Outro: Or we can create colorful designs of our own,

  • through art, photography, or graphic design.

  • And if you wanted to get better at those things,

  • you could try a class on Skillshare, which offers video courses on all those things and

  • more.

  • For example, if you want to learn how to create 3D designs with tons of impact,

  • DKNG Studios teaches a class called “3D Illustration: Creating Isometric Designs in

  • Adobe Illustrator.”

  • They'll teach you how to use relatively simple skills in Illustrator to add a distinctive

  • 3D look to your designs.

  • But if you want to add color to your life in other ways, there are also courses on all

  • sorts of creative methods from fine art to knitting.

  • All in all, there are over 25,000 courses for you to discover.

  • And right now, Skillshare is offering 500 SciShow viewers two months of unlimited access

  • for free!

  • You can check out the link in the description to learn more.

  • [ outro ]

thanks to SkillShare for supporting this episode of SciShow

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Why Aren't Mammals More Colorful?

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    joey joey に公開 2021 年 05 月 11 日
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