[intro ]
Hi everyone!
You got here just in time for a story!
It’s a great one — and it’s about something
that really happened.
This is the story of the Peppered Moth.
A long time ago, most peppered moths had white
or gray wings with little dots on them.
That’s why people called them “peppered,”
because the dots kind of look like pepper.
Instead of sleeping at night like we do, these
moths are awake at night and sleep during
the day.
While they’re sleeping, they like to hang
out on trees.
In some parts of the world, they spend lots
of time resting on a type of tree called a
birch tree,
which normally has light-colored bark with
dark spots on it.
Something called lichen grew on the tree bark,
which made it look even lighter.
That way, with their light-colored wings,
they could blend in with the tree while they
were resting and it would be harder for other
animals, like birds, to find and eat them.
When animals blend in like that, it’s called
camouflage.
But even though almost all peppered moths
had light-colored wings,
there were a few with dark-colored wings with
little light spots on them.
There weren’t very many of them because
it was really easy for birds to spot them
against the light birch trees.
But then something happened to make the light
trees become dark.
About two hundred years ago, people started
building factories,
places where all sorts of things are made.
This was an exciting time because a lot of
stuff was being made, and fast, too — everything
from clothes to huge metal boats.
We actually have a name for this special time:
the Industrial Revolution.
But there was a big problem.
The factories burned something called coal
for energy to power their machines.
They burned so much coal that the smoke made
the air all dirty.
That made those birch trees darker, too.
It was like sprinkling little tiny bits of
coal all over them.4
And remember the lichen that grew on the trees?
The dirt in the air made the lichen die, so
they weren’t there to brighten up the tree
bark.
The darker trees were a big problem for peppered
moths.
It used to be that the light-colored ones
would blend in with the trees,
but now they didn’t, and they really stuck
out.
It was super easy for birds to find them and
eat them,
and soon there weren’t as many peppered
moths as there used to be.
But those few moths with darker wings were
totally fine — now that the trees were darker,
it was easier for them to hide.
Suddenly, more darker-winged moths were able
to live long enough to have moth babies,
which also had darker wings.
And then those moth children grew up and had
more moth children.
So gradually, over many years,
the moths with darker wings became way more
common than the moths with lighter wings.
Scientists call this process natural selection:
when some living things have a trait that
helps them survive,
like the moths’ darker wings, there end
up being more babies that also have that trait.
That’s how peppered moths changed from mostly
having light wings to mostly having dark wings.
But the story doesn’t end there, Squeaks.
When people realized what the new factories
were doing to the air,
eventually they figured out new and better
ways of making stuff without making the air
as dirty.
Over time, the air got cleaner again, and
guess what happened?
The bark on the birch trees got lighter again,
and the lichen started to grow back.
Those moths with darker wings started to stick
out again,
and the moths with lighter wings had an easier
time hiding from birds.
Natural selection happened all over again!
And today, the peppered moths with lighter
wings are much more common than the ones with
darker wings.
That’s where our story ends.
But this was just one example of how one type
of animal changed over time because there
was something that helped some of them survive.
Natural selection happens with all types of
living things, all the time.
It just usually takes too long for us to notice
it as it’s happening.
But it’s how, a long long time ago, humans
became very good at running.
The people who were good at running had an
easier time finding food and running away
from animals trying to eat them,
so they had more babies, and pretty soon lots
of humans could run.
Natural selection is also how rats became
so good at smelling things —
they can smell animals that want to eat them
from far away, so they have time to hide.
There are examples of this type of change
everywhere we look.
In a way, the story of the peppered moth is
a lot like the story of how all life on earth
has come to be.
Thanks for joining us!
If you want to keep learning all sorts of
amazing things about our incredible world
and all the animals in it,
hit the subscribe button, and be sure to check
us out on the YouTube Kids app!
We’ll see you next time, here at the Fort!
[ outro ]
