Name: The Link Between Zebra Stripes and Sand Dunes | Natural Patterns
Uploaded: 2021-05-19T02:56:41.000Z
Duration: 9 min 8 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：

On the northern coast of Ireland, there's a line of cliffs made up of countless pillars

And at the foot of these cliffs is the famous Giant's Causeway — around 40 thousand

of these columns worn down and jutting out into the sea.

People have marveled at these for centuries, because the columns /almost/ look like they're

carefully crafted into a regular, hexagonal pattern.

It's an incredible display of nature, but it's not the only place you can find strange,

You can see something similar just across

the sea, in Scotland's Fingal's Cave, or in a Wyoming rock formation called the Devil's Tower.

But we also see these shapes in other places, like the cracks of drying mud or the glaze on pottery.

In fact, once you start to notice them, you can see that certain patterns, like hexagons,

spirals, and stripes, appear again and again throughout nature, even in phenomena that

clearly have nothing to do with each other — like zebra stripes and sand dunes.

And by studying these patterns, scientists are discovering that many things in nature

seem to share simple, fundamental rules that play out all over the natural world.

Of course, we can't reduce /every/ pattern down to a few simple mechanisms.

But, by taking a close look at the way certain ones arise, we can start to understand how

a few simple principles may unite patterns across the universe.

First, let's get back to Giant's Causeway and those weird polygon-shaped cracks.

Scientists now think those regular shapes may be created by the release of stress.

See, Giant's Causeway formed at a volcanic fissure, where lava spilled onto Earth's surface.

And in general, as lava cools, its surface layer shrinks and solidifies, which puts an

increasing amount of tension on the rock.

Eventually the surface has to release that tension by cracking open.

Now at first, the cracks form at random, and they tend to criss-cross because perpendicular

lines can release the most energy from the rock.

But then, as the lava cools from the top down, each lower layer of lava cracks, also.

Usually, the new cracks form right below the existing ones, because the rock is already a little bit weaker there.

But instead of forming a T shape again, the new cracks literally cut corners to release more energy.

So, as the crack gets deeper, the T shape gets more rounded, until eventually it looks

And if you have a bunch of Y-shaped intersections next to each other, you end up with hexagons.

So, at Giant's Causeway, cracks formed columns in the hardened lava, and as that rock eroded

Meaning that, in the end, this grandiose natural structure was likely all a result of some

And in other natural places where we see hexagons, like the cracks in glaze or dried mud, scientists

It's just that, in these cases, instead of growing deeper, the original cracks are

closing up and then re-forming during cycles of heating and cooling or wetting and drying.

Each time they split open again, they tend to crack along the same lines, but just like

the cracks in lava, they will also cut corners until the T shapes have evolved into Ys.

So, even though a glazed pot and a dry lakebed don't have a lot in common, simple physics

may explain the strangely similar patterns on both of them.

Now, if you haven't noticed the hexagons in nature before, one emergent pattern you've

They might be the one of the most famously striped creatures, but the pattern is far

Animals like tigers, okapi, angelfish, and certain hyenas all wear stripes, too, and

/none/ of them are closely related in terms of evolution.

But they actually /might/ have something in common.

One idea that scientists have investigated for years is that zebra stripes form through

a chemical process called a reaction-diffusion system.

The idea is that, as a zebra's body grows, at little points throughout its skin, cells

start to make a protein or chemical called an activator that does a few things:

First, it signals to skin cells around it to start producing pigment, turning that patch

Second, it tells those cells to create more of the activator.

Since it essentially self-multiplies, the signal from the activator will spread and

This means that, if left alone, even a little blip of this chemical on the zebra's nose

But it /doesn't/ just go on forever, because the activator also does one more thing: It

tells the cells to produce something called an inhibitor.

And an inhibitor is some chemical or protein that puts a stop to the self-multiplying behavior

So, the activator is sending mixed messages: It's creating one chemical that says, “Turn

black and make more of me,” and another, just behind it, that says, “Ignore that order.”

For the first few cells, that second message may come a little too late — the cells are already

destined to become black — but the inhibitor actually moves a little bit faster than the activator.

The reason may vary from one inhibitor to another, but, for example, maybe it's a little smaller.

But either way, eventually the inhibitor catches up, getting its message across in time to

So it ends the stripe and leaves a patch of white.

If you have this scenario play out over and over across the zebra's body, you'll end up

And with a slightly different set-up, the same mechanism can also create spotted patterns,

The thing is, for a long time, this mechanism was purely hypothetical.

It was proposed by the British mathematician Alan Turing, who put out a paper in 1952 outlining

how animal patterns like stripes or spots could emerge through this mechanism.

And chemists /had/ noticed similar, oscillating patterns in chemical reactions since 1910,

But for decades, no one could /prove/ that chemicals like this were creating these so-called

But today, scientists have done a lot more research, and they've spotted what look like Turing

patterns all over nature—in angelfish stripes, giraffe spots, and even the arrangement of

They've even taken things one step further, and in some examples, like the stripey pattern

of ridges inside the mouths of mice, they've been able to nail down the exact identity

of the proteins working as activators and inhibitors.

So, all over the biological world, there are patterns that /appear/ to be related to this

simple mathematical idea that Turing proposed in 1952… including some less obvious ones.

Like, in 2012, scientists even suggested that Turing patterns might be responsible for /fingers/.

Their study found that, in mouse embryos, fingers develop in the signature way that

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The Link Between Zebra Stripes and Sand Dunes | Natural Patterns

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