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On the northern coast of Ireland, there’s
a line of cliffs made up of countless pillars
of volcanic rock, all crammed together.
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,
regular patterns like these.
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
like a Y with equal angles.
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
down, it exposed those Y-shaped columns.
Meaning that, in the end, this grandiose natural
structure was likely all a result of some
pretty basic physics.
And in other natural places where we see hexagons,
like the cracks in glaze or dried mud, scientists
think something similar is happening.
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
almost certainly noticed is stripes.
Take zebras, for instance.
They might be the one of the most famously
striped creatures, but the pattern is far
from unique to them.
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
of skin a certain color, like black.
Second, it tells those cells to create more
of the activator.
Since it essentially self-multiplies, the
signal from the activator will spread and
get stronger over time.
This means that, if left alone, even a little
blip of this chemical on the zebra’s nose
would turn the whole animal black.
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
and breaks the cycle.
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.
In other words, it /diffuses/ faster.
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
stop the activator.
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
with those famous stripes.
And with a slightly different set-up, the
same mechanism can also create spotted patterns,
spirals, or maze-like ones too.
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,
so it did seem possible.
But for decades, no one could /prove/ that
chemicals like this were creating these so-called
Turing patterns in animals.
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
feathers and hair follicles in the skin.
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
is predicted by the Turing mechanism.
If they’re right, that means we could think
of fingers as… maybe just really weird stripes?
But in any case, scientists are still exploring Turing’s
hypothesis — and the mechanism he described
can even be applied to patterns that /aren’t/
biological.
For instance, sand dunes are purely physical
patterns, but you can think of them as following
the same principle of activators and inhibitors.
See, sand dunes form on flat, windy land that’s
full of small imperfections like a boulder
or little ridge.
As the wind blows, it meets those small imperfections,
which break up the air current.
As soon as the current is gone, any dust or
sand the wind was carrying falls and builds
up on the downwind side of the imperfection.
Over time, this little pile grows, and as
it gets bigger, it breaks up more wind and
traps more sand, which lets it get bigger,
and so on.
So in that sense, it acts like an activator:
It creates more of itself.
But it also plays a second role.
That same dune removes sand from the air so
another dune /can’t/ form right behind the first one.
In that sense, it acts like an inhibitor.
So, in a way, the naturally spaced-out ridges
we see in dunes arise from the same principle
that /may/ create zebra stripes.
Of course, these patterns we see in dunes
aren’t /that/ simple — they’re also
influenced by factors like gravity, moisture,
and wind direction, which can have dramatic
effects on how dunes look, even though they
all form out of the same basic principle.
But overall, this shows that, on a basic level,
even patterns that /seem/ vastly different
can just be variations on a theme.
Now, it’s hard to tell exactly how prevalent
and important processes like Turing patterns
or hexagonal cracking are—the universe is
a pretty complicated place.
So as tempting as it is to look for simple,
unifying principles, it’s also important to consider
/all/ of the factors that might be pushing
an organism or landscape to evolve a certain way.
But overall, what looking at these processes
does suggest is that biological and geological
patterns are all grounded in the physical
world.
And by studying how these patterns arise,
when we /see/ those patterns in other places,
we can infer things about what physical processes
are going on there, whether it’s on our
own planet or far beyond it.
So, studying how these patterns arise can
give us a jumping off point to study the universe—and
it’s a reminder that seemingly small interactions
can grow to create something spectacular.
Thank you for watching this episode of SciShow!
And a special thanks to this month’s President
of Space, Matthew Brant.
We couldn’t make all these videos without
the support of people like Matthew and the
rest of our patrons.
And if you’d like to join them and help
us keep making science videos that are available for free on the
internet, you can find out more at patreon.com/SciShow.
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