Hi. It's Paul Andersen and this disciplinary core idea LS4C. It's on adaptation.
Remember the last video we talked about was natural selection which is differential reproductive
success. In other words, each organism is made a little bit differently. And depending
on how they do in their environment, they may survive and pass their genes on. What's
interesting about natural selection is it's the only type of evolution that can eventually
lead to adaptation. In other words organisms that are better suited to their environment.
But what is an adaptation? It's simply a trait. It could be anatomy, like a thumb. It could
be behavior, what we do with that thumb. Or it could be the physiology inside of our arm
that allows all of this to occur. But what essentially it does, it allows us to survive.
So our opposable thumb, in other words a thumb that works in opposition to all the other
fingers allows us to build sophisticated tools like computers. And has really contributed
to our success on the planet. And so that's what adaptations are. And so let me give you
an example of this. One that scientists are really starting to understand. It's the story
of the rock pocket mouse. And it lives in the southwest deserts. And it usually comes
out at night and it does that so it can avoid predators. But it does have certain predators
at night. Those are called owls. And so they all kind of blend in with their desert. But
there's a certain type of rock pocket mouse that has a mutation. It's called the MC1R
gene. And what it does is it causes this dark coloration. So let's look at what rock pocket
mice might look like in their natural environment. And so if we look at this habitat you're going
to see that that black mouse is going to step out and we're going to be able to see it readily.
But the other ones are going to blend in. In others words we can't see them. And so
that camouflage is going to be an adaptation. It's been selected for over time. Multiple
genes have been selected to give them that brown color. But let's say I were to change
the background and make it darker. Did you see all of these mice hiding before? Probably
not. And that's because the blended in. And so could this ever happen? Could the ground
ever turn from this brown color to this black color? Well it actually does. There are volcanic
flows. And so we have this basaltic lava that flows out in this area. It doesn't happen
all the time, but it does happen enough to the point where once you have this black lava
all of those mice that used to blend in are going to show. And they're going to be targeted.
And over time we can see that population change. And so that black could eventually become
an adaptation. We'll get to that in just a second. Another example of one that we see
all of the time is the antibiotic resistance in bacteria. And so bacteria will grow on
this petri dish. It would be this brown, this is going to be billions of bacteria around
the outside. But if we add antibiotics to that, so chemicals that kill those bacteria,
then the bacteria aren't going to be able to grow wherever this disc of antibiotic is
found. But what's going to happen in bacteria is there are going to be mutations constantly.
Over and over and over again. And occasionally those are passed to other bacteria. And so
usually these mutations that cause resistance to antibiotics will be found on a section
of DNA called the plasmid. And so let's look at natural selection at play. This is all
of the bacteria before the selective pressure occurs. And they each have different levels
of resistance to the antibiotic. So low resistance to high resistance. And so if we apply an
antibiotic to those bacteria it's going to kill all of those with low resistance. And
so after the selection we're going to have a final population that is better evolved.
Or it's adapted to that environment. And so if we take one of these bacteria and apply
those same antibiotics to it we're going to find that in areas like this, it doesn't effect
the bacteria at all. Sometimes it knocks them down a little bit but in general they're not
being effected by a lot of these antibiotics. And so this is evolution. It's natural selection
occurring. In this case we have a physiological response. In other words they're blocking
the action of that antibiotic. And so all life on our planet, all of the beautiful diversity
of like on our planet came through this slow mutational changes which are then played agains
the environment. And so a polar bear looks wonderful. It blends in with the snow. It's
really heavy. And so it can survive in that cold climate. It's perfectly adapted to that
climate. Likewise the dolphins have this beautiful streamline. And the giraffe has its really
long neck. And so it's not like they're making those adaptations occur. It's not like the
giraffe is somehow stretching its neck. It's just that during a time of drought, giraffes
that happened to have a slightly longer neck are going to do better. And what about polar
bears right now? I mean right now we're seeing increases in the global temperature. What's
that going to do to the polar bears? Well the ones that are really, really heavy are
going to be over heated. And there's not going to be a need to go out on the ice pack and
hunt seals if you can't get out on the ice pack. And so what we'll see is that some of
those adaptations aren't helpful anymore. And so we'll probably see a change in characteristics
or adaptations of polar bears over time. Maybe they'll become lighter. Maybe they'll start
to hunt salmon like grizzly bears. And so we'll see that change over time. So what's
the teaching progression? How do you introduce this to students? Well you want to start in
the lower elementary grades by talking about the requirements of life. And so if we have
a rabbit like this, it's going to have certain characteristics that allow it to survive in
its environment. But tell your students that if that environment changes, let's say it
get really really hot or really really cold, then they may not do as well. If we were to
get a huge glacier move into an area, some of those rabbits that were perfectly adapted
before are going to die. As we move into the upper elementary grades we want to start talking
about how the habitat or the living organisms start to interact. And so let's go back to
that rock pocket mouse again. So here's our habitat. We've got a bunch of mice that are
perfectly adapted to this environment. But what happens if we have a change? What happens
if we have this lava flow and all of a sudden the rock has this really dark appearance?
Well we've changed their habitat. And now natural selection is going to occur. So imagine
it's night time and this owl is now hunting these rock pocket mice. Which ones are going
to show up more readily? It's going to be the light mice. And so over time the owl's
going to start to target them. And what's going to happen to this dark color? Well that
may become the adaptation. And we see this when scientists are looking in the deserts,
they're finding that in areas where you have this basaltic rock, we're going to have more
of these dark mice. And in areas where that's not present we're going to see more of the
light mice. As you move into middle school you want to start to introduce this idea of
speciation. Remember speciation is the formation of a new species. And so imagine if we have
two adjacent areas in a desert. One where they're really dark in color, because they're
perfectly adapted to that rock. And one where they're really really light. What could eventually
happen over time, well if there's enough change in their DNA, there's enough change maybe
in their mating strategies, those could eventually form new species. And this is the big thing
that Darwin said. This idea that all life came from one common ancestor. And all the
diversity we have on our planet came through small changes in the environment. And then
species adapting to that. As we move into high school we really want to talk about the
steps of natural selection. And there's really four steps or four factors that species go
through as they become better adapted to their environment. Number one is this idea of reproduction.
We have to have enough of those organisms and the ability to make more and more of them.
We also have to have variation in that population. So with these mice it was going to be variation
in their coat color. But in us it might be variation in our behavior or in our height.
Or even in the action of our thumb. What happens next is we have competition. In other words
there's going to be competition between those organisms. On a really dark area, then the
light mice are going to be targeted. And vice verse on a really dark or on a very light
area. What eventually happens is the survivors will proliferate. In other words they're going
to do better. And that can eventually lead to a new population. Reproduction begins again
and this goes over and over and over again. And so adaptation is a process. It's how species
become better adapted to their environment. The mechanism is natural selection. And I
hope that was helpful.