(bright music)
- Welcome back, scientists.
This is Ms. Jetha from
Seattle, Washington,
bringing to you lesson
six of natural selection.
Now if you haven't had a chance
to watch lesson four or lesson five,
make sure you go back and
watch those two lessons
which will help everything come together
a little bit more.
So here we go with lesson
six of natural selection.
Here's what you'll need for this lesson.
A pencil or a pen.
Some lined or blank paper.
And optional but encouraged,
a family member, friend, or
a pet you can check in with,
and a lesson six packet
that was provided to you
by your teacher.
Let's go ahead and warm up.
Pause the video and read
"Sherman's Story #3"
right here on the right-hand side.
Turn and talk to a
friend, a family member,
or jot your responses
down on a piece of paper
about the following questions.
What do you think Sherman is right about?
And what do you think
Sherman is wrong about?
Carefully read the dialogue
between the two characters
and see where do they go right
and where do they go wrong.
Here's what I noticed here.
In our illustration we
have green dragonflies
and brown dragonflies.
Now what we know is
that in this environment
many years of lots of rain
caused the environment to
become very lush and green.
Now Sherman understands clearly
that the brown dragonflies all got eaten
because their predator
could see them more easily
in the green environment,
and he understands that green, therefore,
is an adaptive trait for
the green dragonflies.
And that's because being
green helps them to camouflage
and thus survive and reproduce more.
Now what Sherman doesn't have
correct here is when he says,
"The very same green dragonflies
are still alive today."
That's not true.
What we see is that
these green dragonflies
must be as a result of being the offspring
of green dragonflies generations ago.
We know that those green
dragonflies probably have died
and thus the offspring
carries on the trait,
which was adaptive, for being green,
because it can survive and reproduce more.
And thus in the environment
now we have more green
than brown dragonflies.
We are now gonna read an article
called "The Deadly Dare."
Follow along with me as we learn more
about the poison that
rough-skinned newts carry.
"The Deadly Dare."
"Rough-skinned newt defenses.
"In 1979, friends dared a
29-year-old man in Oregon
"to swallow a living rough-skinned newt.
"The man didn't realize
"how poisonous rough-skinned newts are.
"A lethal, fast-acting poison
called tetrodotoxin, or TTX,
"oozes from their skin.
"The man swallowed the newt whole
"and started feeling
weak a few minutes later.
"He described a numb
feeling all over his body.
"His friends tried to
take him to a hospital,
"but he refused.
"Just 20 minutes later, the man was dead.
"Of course, the newt the
man swallowed died, too.
"In that particular case,
"being poisonous didn't help
that individual newt survive.
"If newts have to be eaten in
order to defend themselves,
"being poisonous doesn't sound
like a very good defense.
"How is being poisonous, having
a high level of TTX poison,
"an adaptive trait for
a rough-skinned newt?"
All right, so I'm seeing here
that tetrodotoxin is
the name of the poison
that oozes from the
rough-skinned newt skin,
and we are going to be
talking about that a lot more
in terms of how having this
high level of TTX poison
is in fact a good defense
and an adaptive trait.
"Why poison is adaptive.
"One reason TTX is adaptive
is that it acts quickly.
"A predator that tries
to eat a poisonous newt
"may become sick before
it's able to kill the newt,
"allowing the newt to escape.
"In fact, TTX acts so quickly
that sometimes predators die
"before finishing their meals.
"Scientists have observed
rough-skinned newts
"crawling out of dead
or paralyzed predators.
"Even more important,
"predators can smell and taste TTX poison.
"The main predator of rough-skinned newts
"is the garter snake.
"Scientists have found
evidence that garter snakes
"use their senses of smell and taste
"to tell whether a rough-skinned newt
"is too poisonous to eat.
"They have even observed garter snakes
"doing quick taste tests,
"licking rough-skinned newts
"before deciding whether to eat them."
That's really interesting,
and I wanna make a note here
'cause I'm having a question
about how they observed that.
So I'm gonna document
my question right here.
How did scientists
observe this?
How did they know
that the garter snakes
were choosing which newts to eat?
"Scientists have studied
whether garter snakes
"are able to detect TTX poison in newts.
"Biologists have placed one
newt and one garter snake
"together in a cage
"to see whether the snake
would eat the newt."
Oh, okay, so that's how they were testing
how these garter snakes
detect the newt poison.
They put a newt and a garter
snake in a cage together
and then documented what
happened afterwards.
"They have tried this
test over and over again,
"using different snakes
and different newts.
"Even though the newts are placed
"directly in front of the snakes,
"not every newt gets eaten.
"Biologists are able to consider
"the cause-and-effect relationship
"between high poison levels
and survival in newts
"by examining a population
of newts with high variation.
"The newts in the test
ranged from having no poison
"to having very high levels
of TTX in their bodies."
Okay, so they were able
to have a range of newts
with different poison levels
and therefore determined the relationship
between the garter snakes
being able to detect the poison
because they were able to see which newts
that the garter snakes could eat,
or chose to eat, I should say.
"In these tests, the snakes
consistently eat the newts
"with the lowest levels of TTX
"and do not eat the newts
with high levels of TTX."
So this is part of the evidence
that they gathered here.
So let's make sure we document that
by underlying it in our reading.
"These results are evidence
"that garter snakes can detect TTX
"and that they prefer to
eat rough-skinned newts
"with lower levels of TTX.
"The more poisonous a
rough-skinned newt is,
"the less likely it is to
be eaten by a garter snake."
So, because they had a large variation
of newts with different poison levels,
they could see, then, how
the snakes would react.
And they concluded that the more poisonous
the rough-skinned newt is,
the less likely it was to
be eaten by a garter snake.
So the snakes only ate
newts with low levels of TTX
and chose not to eat the
newts with high levels of TTX.
"That means high levels of
TTX are an adaptive trait
"in rough-skinned newts that
live near garter snakes."
So it seems like they're saying here
that high levels of TTX are adaptive
because they're allowing
the newt to survive more
because from the test they could see
the garter snakes would choose not to eat
the newts with high levels of TTX,
so therefore it must be adaptive
because it allows the
newts to survive longer.
Oh, on this page here I see this picture,
and I'm wondering what that is,
so I am going to read the caption
so that I can figure that out.
"A rough-skinned newt's poison
"is a type called
tetrodotoxin, or TTX for short.
"This is a model of a molecule of TTX."
Oh, okay, so this helps me understand
that TTX is a molecule,
so it's definitely very small,
and I remember that when scientists
have something very small
that they cannot see
they tend to make models out of it
so they can visualize
it a little bit better.
So I can see here now that
this is a model of TTX poison
that we have been reading about.
"How Adaptive Traits Spread.
"If snakes are in its environment,
"a poisonous newt is less
likely to die from being eaten
"than a newt that isn't poisonous.
"The newts that don't get eaten
"have a better chance of living longer,
"and that's important because it means
"more chances to reproduce.
"Organisms have to reproduce
"in order to pass on their genes,
"which are the instructions
for making protein molecules
"that determine traits.
"If they don't reproduce,
their traits die with them."
Wow, that's really important.
I'm gonna make a flowchart
to help me remember that.
So, what this is saying here
is that organisms survive.
And when they are able to do that,
because they have this adaptive
trait of being poisonous,
they're able to survive
and then reproduce.
And when they reproduce,
they're able to pass down
their genes to their offspring.
Okay, that helps me kind of
recognize a little bit more
about the relationship
between all these processes.
Let's see how this helps us understand
how being poisonous in the new population
became more common.
"In the new population,
"more poisonous newts are more likely
"to survive long enough to reproduce
"and pass down their genes,
"and therefore the trait
of being poisonous,
"to the next generation."
Okay, so these organisms
that are surviving
are in fact poisonous newts.
So these poisonous newts
are then able to reproduce
and pass on this gene for
being highly poisonous
to their offspring.
"As a result, there will be more and more
"highly poisonous rough-skinned
newts in each generation.
"This will cause the
distribution in the population
"to change over many generations.
"Scientists call this
process natural selection."
Okay, here is the main
word of our unit, folks.
Natural selection.
And this in-text definition
says it is in fact
a change in the distribution
of traits in the population
over many generations.
"This process does not only
happen in rough-skinned newts,
"it has been observed in
populations of different species
"all over the world."
Okay, so this is how natural
selection ties into everything.
The organisms that survive
are those that are most poisonous,
and therefore they then reproduce
and they're passing down their genes
of being highly poisonous
to their offspring.
And then those offspring
are now poisonous,
and then they, the ones
that are most poisonous,
will then reproduce,
and then they pass down their
genes to their offspring,
causing a change in the
distribution of poison level
over a period of time.
And that is what we
call natural selection.
So, now I'm wondering what other organisms
experience natural selection,
this change in distribution
of traits over generations.
Let's find out.
"Other poisonous organisms.
"Being poisonous is an adaptive trait
"for many different organisms,
"not just rough-skinned newts.
"There are many poisonous plants,
"such as deadly nightshade,
hemlock, and mint."
Wow, mint, not something
I would have expected.
"You might be surprised
to see mint on this list
"since you've probably
eaten mint yourself.
"The poisons in mint
are harmless to humans
"but deadly to some plant-eating insects.
"These poisons are what give
mint its minty taste and smell.
"They're warning signals to
tell insects to stay away.
"Like rough-skinned newts,
"poisonous plants are poisonous
"as defense against being eaten.
"Plants can't run away from
animals that want to eat them,
"so they have to defend
themselves in other ways
"with adaptive trait like
tough bark, sharp thorns,
"and being poisonous."
Wow, I never thought of a plant
as having a defense mechanism.
Here are a couple of examples on the left,
let's read a little bit more about them.
"A deadly nightshade,"
which is here on the left,
"is an extremely poisonous plant.
"Eaten just a few
berries can kill a human.
"Mint," on the right, I've
definitely seen that before,
"is harmless to humans but
deadly to some insects."
Here are some other plants
that I kind of recognize
from some of my adventures.
Acacia thorns, redwood
bark, and cactus spines.
Cactus spines I definitely knew about,
and I've definitely experienced
how sharp they are before.
"Besides poison, plants'
defenses include sharp thorns
"and thick bark."
So those provide
protections for the plants
from being eaten,
sometimes maybe from
being eaten by humans.
We just finished reading
"The Deadly Dare" article
and let's make sure that we comprehend
some of the main important points.
Grab your pen or pencil,
grab your notebook or piece of paper,
whatever you've been taking notes on,
and turn and talk to a
friend or family member
or jot your responses
down on a piece of paper
about the following questions.
Number one, what is the
definition of natural selection?
Number two, in the study
that scientists conducted
where garter snakes were
paired with newts in a cage,
why did the garter snake
sometimes eat the newt
but other times did not?
And number three, how did
more highly poisonous newts
end up in the population
generation after generation?
Why is every generation more poisonous
than the generation before?
Go ahead, grab your pen or pencil,
and let's make sure we comprehend
some of these important
parts of the reading.
Let's go ahead and tackle
these questions together.
Number one, what is the
definition of natural selection?
Key word in our unit, right?
Grab your pen or pencil,
we're going to go over
this definition together.
Natural selection is the process by which
the distribution of traits in a population
changes over many generations.
So I remember in our context
what we're talking about here
is poison level,
so the change in our population of newts
from becoming less
poisonous to more poisonous,
that is an example of
natural selection happening,
that process of what is going
on there is natural selection
because there's a change
in the distribution
of the trait of poison level.
Question number two.
In the study that scientists conducted
where garter snakes were
paired with newts in a cage,
why did the garter snakes
sometimes eat the newt
but other times did not?
Well, from our reading,
in the article it said that
garter snakes can detect
the poison level of rough-skinned newts
by smelling and tasting the TTX poison,
and sometimes garter snakes ate the newt
because they understood
that it was a low enough TTX poison level
where they would still be able to survive
when they ate the newt.
Comparatively, they
chose not to eat the newt
when they detected the
poison level as too high,
knowing that they would
not be able to survive
after eating that particular
newt with a high poison level.
So that's why sometimes they ate the newt
and sometimes they didn't.
Question number three.
How did more highly poisonous newts
end up in the population
generation after generation?
Why is every generation more poisonous
than the generation before?
Well, we know that having
the trait for poison
is an adaptive trait and helps the newts
to be able to survive longer.
And when they survive longer,
they're able to reproduce.
And in that process of reproduction,
they are passing down their
genes to their offspring,
and specifically the
gene for having the trait
of high poison level.
So they're passing down those genes
which are providing instructions
for making the protein
that carries the trait for
having a high poison level.
So their offspring then have this trait
for high poison level,
and then that continues
back into the cycle.
Those offspring are surviving,
they're reproducing,
and then passing on their
genes for poison level
to their offspring as well.
So that's how this process goes
in terms of poison level being passed down
generation to generation,
and therefore allowing the population
to reflect that as well.
We're gonna see a
diagram in the next slide
that will help us illustrate this
a little bit more concisely.
I can see the title of this diagram is
"How Natural Selection Works,"
and there are lots of
different symbols here
so I'm gonna make sure I read the key
and understand what each
of these symbols means.
These red dots symbolize
the amount of TTX poison,
an X symbolizes death,
and these little lines that
kinda look like a track
mean reproduction.
So let me look at each panel here
and see what I notice in what's going on.
"There are different inherited
traits in the population."
Okay, so this is my whole
population of newts,
and I have five newts with one dot
to symbolize a low amount of poison.
I have five newts with kind
of a medium amount of poison,
they have three dots.
And then I have five newts with six dots
to indicate a high poison level.
In panel two it says,
"Adaptive traits help organisms survive
"in their environment.
"Organism with adaptive traits
"are more likely to survive
long enough to reproduce."
Okay, so I remember
poison level is adaptive,
so that definitely is demonstrated
in what I'm seeing here.
Those newts with a low poison
level, with only one dot,
many of them have died,
and even some of the newts
with a medium poison level
have died as well,
and one newt with a high
poison level has also died.
However, those newts that still exist
have been able to reproduce.
So there's one newt
with a low poison level
that was able to reproduce,
two newts with a medium poison level
that were able to reproduce,
and then four out of the
five with a high poison level
were able to reproduce.
So, "The organisms that reproduce
"pass on their traits
to the next generation."
So I can see here this is now
what my population might look like.
These four newts have reproduced
and so now we have a larger number
of newts with a higher poison level,
and the medium newts have also reproduced
so then we have a larger number of newts
with a medium poison level,
and even the one with the low poison level
has also reproduced,
so there's still lots of
variation in this population,
but the distribution of poison level
definitely is leaning towards
those with high poison level,
which totally makes sense
because poison level is an adaptive trait
that helps these newts survive
and therefore reproduce.
So we can see that the
survival of these newts
allowed them the opportunity to reproduce,
which we can see in the final panel here
in this population that we end with.
I want you to turn and talk
to a friend or family member
or jot your responses
down on a piece of paper
with your pen in your
notebook or lined paper,
and I want you to
explain in your own words
why are there more newts
with high poison level
in the population in diagram three.
So these newts here,
why are there higher number of newts
with a high poison level in this diagram
compared to the diagram one here
where we only have these many newts
with a high poison level?
Turn and talk to your neighbor
or a family member here,
pause the video,
and I want you to try and
explain this in your own words.
When we talk to someone and
explain it in our own words,
we are therefore able to
understand a little bit more
about what's happening here.
So pause the video now, talk with someone,
and we'll come back in just a second
to understand what we learned.
All right, I hope you were able
to explain in your own words
to your friend or your family member
that there were more newts
in this population in diagram three
than in this population in diagram one
because those newts had the adaptive trait
of high poison level
that allowed them to survive longer
and thus have the opportunity
to reproduce more.
So, because these newts
were able to survive,
they were able to reproduce
and therefore caused a
higher number of newts
with high poison level
in the ending population.
And what we can extract from
this is this key concept.
Grab your pen or pencil
and your notebook or your
lined paper or your tracker,
wherever you're keeping
track of these key concepts.
And we can extrapolate
this from what we just saw
in that diagram.
Individuals with adaptive traits
are more likely to live
longer and have offspring.
Individuals with non-adaptive
trait are more likely to die
without having offspring.
We also saw that in our simulation
from last lesson as well.
Those organisms with adaptive traits,
whether that be poison level
or the adaptive trait of ostrilope color
that matched the environment,
those organisms are able to live longer
and then have offspring.
And the individuals
with non-adaptive trait,
whether that be a low poison level
or an ostrilope color that
does not match the environment,
they're going to be eaten quicker
and they're more likely then to die
without having offspring.
This information that we just
gathered from our article
as well as from this diagram
that we just analyzed together
will help us as we circle back
to our chapter two question below.
And that chapter two question was,
how do individuals in a
population get their traits?
Pause the video right now,
and I want you to turn
to someone near you,
talk to someone, you can
text someone if you want,
and respond to this question
now that we have the
understandings that we have
about natural selection
and how individuals in a
population get their traits.
So pause the video and
respond to this question,
discuss it with someone
so that we can further
develop our understanding
and our scientific skills of explanation.
This is really exciting.
We just got another message
from Dr. Alex Young,
who's the head biologist
at Oregon State Park.
Let's see what he has to tell us.
"I hope you're making progress
"in your investigation of the
poisonous rough-skinned newts.
"We're hoping to share your
explanation with park visitors
"as soon as possible.
"Can you explain what you know so far
"about the newt population?
"We would really appreciate
if you could send over
"a scientific argument
that connects your evidence
"to your claim and reasoning.
"That will really help our visitors
"understand more about the newts."
So it seems like he wants
us to create an explanation
that these visitors can understand
as they learn more about newts
and other organisms in the park.
I'm sure you all remember
how to write a scientific argument,
but let's just do a little refresher.
In a scientific argument,
we always start with a question
about the natural world.
For us, that question is,
how did the rough-skinned newt population
become more poisonous over time?
We then make a claim,
which is a proposed answer to a question
about the natural world.
And then we support that
claim with evidence.
Evidence is information
about the natural world
that is used to support or go
against or refute the claim.
And we can use evidence
which comes from our
articles in our reading,
the simulations that
we have done together,
and anything else that you
might want to incorporate
into this argument
that supports the claim
that we have done or seen
in this unit.
We then use scientific reasoning, folks.
We talk about those scientific principles
that support our evidence
and connect that evidence to the claim.
The claim that we are gonna make
for this scientific
argument is the following.
The claim is, "The new
population became more poisonous
"because the snakes in this environment
"caused poison to be an adaptive trait,
"and poison level 10 is the most common
"because the newts with this trait
"were able to live
longer and reproduce more
"than other newts."
So I wanna challenge you to
write a scientific argument
that responds to this question
and supports this claim.
You can even write your
own version of this claim
if you would like
and support it with
evidence and reasoning.
You may wanna share this with your teacher
or a family member or a friend as well
as you are sharpening those
scientific argumentation skills.
Grab a pen or pencil, grab some paper,
you can also type this if you want to,
and challenge yourself by
writing a scientific argument
that helps us respond
to this unit phenomena
about how the rough-skinned
newt population
became more poisonous over time.
Let's summarize what we
learned in this lesson.
Poison can serve as an adaptive trait
if predators detect the poison
before killing their prey.
Organisms with adaptive
traits are less likely to die
than organisms with non-adaptive traits,
which means that they have more
opportunities to reproduce.
And individuals with adaptive traits
are more likely to live
longer and have offspring.
Individuals with non-adaptive traits
are more likely to die
without having offspring.
Make sure you include some of these
in your written scientific arguments.
You might also wanna include
some of the key concepts
which are scientific principles
that can serve as reasoning
to connect your evidence with your claim.
Thanks for joining me for lesson six
in our natural selection unit.
(bright music)
(rock music)
