Name: Why Aren't Mammals More Colorful?
Uploaded: 2021-05-11T13:55:59.000Z
Duration: 5 min 57 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

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

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

The evolutionary reason for mammals' subdued coloration is more complex than you might

-- 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

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.

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

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.

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

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

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

We know mammals have the /capacity/ to be more colorful.

The most likely explanation is that mandrills, birds, and butterflies all share an ability

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,

[DYE-kro-matt-ik] But most mammals only have two types of cones,

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.

Most primates – including ourselves – are 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

Even with our fancy third set of cones, though, our color vision isn't as good as many of

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

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

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

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

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

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

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

Only certain mammals – like primates –

have separately evolved more complex color vision, and with it, more colors on their