Transcript File

An Introduction to the Theory of
Evolution
By: C. Chary
Learning Target
• LT BI8.a*: I can explain how “natural
selection” determines the differential
survival of groups of organisms.
Natural Variation
The differences between
individuals of the same
species.
If there was no natural variation,
all organisms of any species would
All three of these giraffes are the same species, but they have some
differences too. These differences are called natural variation.
look exactly alike!
Natural Variation
I’m a giraffe
too.
Hi. I’mHi,
a giraffe.
I have
a I have a
pretty
long
neck
so eat
I can eat many
longI neck
so
I canthe
easily
Hi. I’m a giraffe too.
can’t
reach
ofonthe
leaves
on Itall
trees. I can
leaves
tall
trees.
also
leaves up high since I’m too
short,
buttougher
I
also
eat
the
plants near the
have
long
legs
and
can
run
have strong jaws and can
chew Ithe
ground.
have short legs, so I can’t
fast.
tougher plants nearer to the ground.
I too fast.
run
have shorter legs and a smaller body than
my friends, but I can run really fast!
Adaptation
A trait that helps an organism
survive in its environment
Adaptations can be physical
(something an organism has)
or behavioral (something an
organism does)
Fitness
The ability of an organism
toplants…
survive
Giraffes eat
and reproduce in its Some
environment.
are short
and easier to
Let’s take a lookreach,
at but
the
the
leaves are
giraffes’ environment
tougher to eat.
Some plants are
tall, and their
leaves are hard to
reach
Giraffes
have
Lions
can runalso
pretty
fast
predators
their
and
hunt iningroups
environment.
I can find food
and outrun most
of my predators.
I have a high
level of fitness.
I can find food
easily. Even
though I’m slow,
I can still outrun
some lions. I
have an average
level of fitness.
I can find food
easily and can
outrun almost
any lion alive!
I have an
extremely high
level of
fitness.
The Struggle for Existence
The competition within and between species to survive and reproduce.
All of the giraffes compete with each
other and other species to survive in
this environment.
What
would
happen
if
this
One thing is for sure…
environment changed and there
The
were no more short trees?
environment
will always
change.
I can still find
food and outrun
most of my
predators. I still
have a high level
of fitness.
I can still find
food easily. Even
though I’m slow, I
can still outrun
some lions. I still
have an average
level of fitness.
Since I have a low level
I can’t
findIenough
to
of
fitness,
probably
won’teat.
survive.
IMy
still
can outrunare
almost
adaptations
not
anygood
lion alive,
that
in thisbut
new
won’t matter
if I starve.
environment.
I Ihave
a very
low level
won’t
reproduce
andof
fitness.
pass on my
“short” genes
to future giraffes.
Even though I can find food, I will probably
get caught by a lion sooner or later.
Because of my low level of fitness, I won’t
survive and pass my “slow” genes to future
giraffes.
Survival of the Fittest
Organisms with the
highest level of
fitness will survive
and reproduce
more successfully.
Natural Selection
Over time, natural
selection results in
changes in the inherited
characteristics of a
population.
These changes increase a
species’ fitness in its
environment
Natural Selection
Let me
translate this
for you…
had thenatural
highest level
Over Itime,
of fitness.
selection results
in
a better
chance
changes Iinhave
the
inherited
to survive and
characteristics
of a
reproduce.
population.
I will pass on my
adaptations to my
changes
increase
offspring,
These
a
species’Over
fitness
its
time, allin
giraffes
will have longer necks
environment
and faster speed.
Natural Selection
Over
It is time,
important
the average
to understand
giraffe
that
has a
these
longer
changes
neck than
takebefore.
millions
This
of years
change
to in
happen…
a species
evolution
over time
is
aisvery
called
slow
evolution.
process.
Natural Selection
Even though these giraffes look similar.
They still have differences between them.
Some are bigger or faster. Others may be
What
arehardier,
thesehairier,
differences
smarter,
stronger,
between
individuals of the same
meaner, or have better stamina
species called?
or camouflage.
Descent with Modification
Each living species has descended, with
changes, from other species over time.
Common Descent
Each living species came from
common ancestors. If we
look far enough back, we can
find the common ancestor for
all organisms.
An Introduction to the Theory of
Evolution
THE END