Name: _________________________________________
Date: ___________________ Period: _____
Natural Selection – Application of Selective Pressures
The four steps of Natural Selection identified by Charles Darwin: 1) overproduction, 2) genetic variation, 3) survival struggle, 4)
successful reproduction. Larger organisms tend to produce less offspring than smaller organisms, so the examples below do not
reference the overproduction mechanism of natural selection.
Key Components
1. Variation
within a
population
2. Environmental
Challenge
(selective
pressure)
3. Adaptation
4. Reproductive
success
Explanation
Example Giraffe
Example: Dinosaurs
Within any population of
living things their traits
________ from individual
to individual.
When the environment
changes available food,
shelter, or water are
affected and this affects
a population’s ability to
___________.
Ancestors to giraffes
had different length
__________.
The population either has
variations that them a
competitive ___________
and they survive or they do
not have traits well suited
to the new conditions and
they die.
Living things pass on their
characteristic to their
____________. The
longer they live the more
offspring they will produce
with that trait.
The giraffe ancestors
with _____________
necks could reach food
higher in the trees and
were able to survive
where those with shorter
necks did not.
The giraffe ancestors
with longer necks were
able to live long enough to
_____________and
their offspring also had
long necks eventually
evolving into giraffes as
we know them today.
Dinosaurs were large and small
___________, there were meat
and plant eaters, they lived in
many different areas.
There was a
________________ event, an
asteroid hit the Earth. The
asteroid caused tidal waves and
sent dust into the air which
blocked the sun for months
changing he climate and killing
plants and animals.
Dinosaurs were unable to adapt
to the catastrophic changes
taking place on Earth and this
lead to one of the largest mass
__________________ in
Earth’s history.
The climate _________
became drier and there
was less and less food
available. Animals which
could get to food would
survive, while the others
could not.
Dinosaurs did ____________
live to reproduce and they
became _____________.
Name: _____________________________
Date: ____________ Period: _____
Key Components of Natural Selection in Action
1. The Florida Panther is an endangered species; there are less than 100 left. Because there
are so few there is not much variation in the population. Humans are creating an environmental
challenge by building on the land in which they live. Explain what might happen to the Florida
Panther and why?
2. What do you think can be done about the Florida Panthers?
Cockroaches in Action
The cockroach is also one of the hardiest insects on the planet, capable of living for a month without
food. It can also hold its breath for 45 minutes and has the ability to slow down its heart rate. It is
popularly suggested that cockroaches will "inherit the earth" if humanity destroys itself in a nuclear war.
Cockroaches do indeed have a much higher radiation resistance than vertebrates, with the lethal dose
perhaps 6 to 15 times that for humans. However, they are not exceptionally radiation-resistant compared
to other insects, such as the fruit fly. The cockroach's ability to withstand radiation better than human
beings can be explained in terms of the cell cycle. Cells are more vulnerable to effects of radiation when
they are dividing. A cockroach's cells only divide once when in its molting cycle, which at most happens
weekly. The cells of the cockroach take roughly 48 hours to complete a molting cycle, which would give
time enough for radiation to affect it but not all cockroaches would be molting at the same time. This
would mean some would be unaffected by the radiation and thus survive.
The following statements contain information regarding the roach populations;
A) Roaches that live to maturity may mate and produce offspring.
B) A population of roaches contain some pesticide-resistant roaches and some that are not
resistant to pesticides.
C) Many roaches do not survive because they come in contact with pesticides
D) Roaches lay many eggs (100 per mating up to 400 in a lifetime)
3.
4.
5.
6.
Which of the
Which of the
Which of the
Which of the
above statements most closely describes genetic variation?________
above statements most closely describe successful reproduction?____
above statements most closely describes overproduction?______
aove statements most closely describes the struggle to survive?_____
Cut out the pictures and place them in the correct place in
the table to illustrate the concept of natural selection in
giraffes.
Cut out the pictures and place them in the correct place in
the table to illustrate the concept of natural selection in
giraffes.