Hi it's Emma Lu and in this video, we'll be
talking about natural selection relates to
a population's environment.
Let's start by looking at nature. So in nature
we often find that animals appear to be perfectly
adapted to their environment. Here are some
examples of these adaptations.
This is a hummingbird, if we look at this
bird. We see that it has a long beak. This
beak fits perfectly to the tubular shaped
flower, its food source. Without this long
beak, the humming bird wouldn't be able to
reach the nectar deep down in the flower.
Thus, it would not be able to eat and survive.
Here we have an owl which is blending in perfectly
with its environment or its surroundings.
Lastly, we have an arctic fox. The arctic
fox exhibits thick fur which allows it to
be protect against the cold climate it lives
in. And the white fur allows it to be camouflaged
and blend in with the snow in the background.
These are some good examples of adaptations
that the animals have with their environment.
However, the question really remains is HOW
THIS CAME TO BE? HOW ARE THE ANIMALS SO PERFECTLY
ADAPTED TO THEIR ENVIRONMENT?
This is answered by a theory called: Natural
Selection.
Natural Selection is a theory proposed by
English Naturalist, Charles Darwin, in the
19th century.
In a nutshell, Natural Selection is the process
in which the fittest phenotype of a specie
will survive and reproduce to pass on their
fit traits. And over time, this lead to changes
in the traits of the living thing or adaptions
and eventually, evolution.
Here is an example that can help you better
understand how this concept works. We begin
by seeing an original population of a specie.
Within this specie, we can see different individuals
with different resistance levels. This is
called variations. In this case, the high
resistance level individuals have a beneficial
trait vs. the low resistance level because
the high resistance ones survive and low-resistance
dies. As the high resistance phenotype survives
and reproduces, the Natural Selection is apparent
and we are left with a population of high
resistance species.
But what is making this selection? Well, the
environment. The environment is the depending
factor on how the selection is made. In this
case, if we apply that the environmental factor
is alcohol, then the ones that are high-resistance
to the alcohol will survive. Of course, the
factor is always changing depending on different
environments. Thus, we see different selection
is made in different environments!
When Darwin was coming up with his theories,
he encountered two species that helped him
along. The Finch - we can see that because
the finches had to survive in different environments,
they were selected differently and resulted
in different traits. But they all started
off with one ancestor with slight variations.
Similarly, the tortoise developed different
shell types depending on different food sources
 
Now to really emphasize on how environment
can affect the Natural Selection process is
through the classic example of the pepper
moth.
There are two variations to the pepper moth.
One is light and one is dark. They live on
light colored trees. As we can see, while
the light moths are camouflaged (this trait
is selected FOR), the dark ones are highly
visible (this trait is selected AGAINST).
Exactly why this selection process is FOR or AGAINST for the peppered moth
is that if the predator, the birds, cannot see the moth then they will be less likely to eat it
Which leads to higher survivability (if you can survive then you have beneficial traits - selected FOR)
This (the light color blending in) led to the
pepper moth population to be more commonly
light in color. However, in 1895, Industrial
Revolution changed the entire selection process.
The trees started turning darker as a result of pollution
The dark
colored moths are now not visible and the
light colored is! What was once selected for
is now selected against.
 
We can see that the determine factors for
Natural Selection is really
dependent on the environment the population
is in.
I've been talking a lot about environment
but what does environment really refer to.
Environment is really the surrounding or condition
in which an organism lives in. It includes
abiotic factors - non-living components such
as temperature, climate, light and more. It
also includes the biotic factors - living
components such as disease, animals, and all
living things in the area.
We refer to the abiotic and biotic factors
that cause Natural Selection to make selections
as Selective Pressure.
Selective pressure is any phenomena which
alters the behavior and fitness of living
organisms within a given environment. It is
essentially the biotic and abiotic factors
in the environment that affects how will an
organism is able to survive.
It is related to natural selection as Selective
Pressure drives Natural Selection which drives
Evolution.
To end this off, I would like to summarize
some key ideas. First of all: Natural selection
is basically the idea that phenotypes with
better traits suited for its ENVIRONMENT will
survive and reproduce - passing on their traits.
Thus, Environment DEFINES the selection.
So, a change in the environment can cause
a change in how a trait is selection for or
against.
(We can see this in the pepper moth example
where what was once selected for may now be
selected against)
Lastly, I want to emphasize on this point
here:
The Environment of the Population or the Selective
Pressure that exists in the Environment of
the Population DRIVES the Natural Selection
which DRIVES evolution.
That concludes my presentation and thank you
for listening!
