Download review

Name _____________________________
Assignment # ______
Natural Selection Worksheet
1. Read the following situations below and identify the key concepts of Darwin’s natural selection.
There are 3 types of polar bears: ones with thick coats, ones with thin coats and ones with medium
coats. It is fall, soon to be winter. The temperatures are dropping rapidly and the bears must be
kept warm, or they will freeze to death. Many of the bears have had ~2 cubs each but due to the
extreme temperatures, many mothers only have one cub left.
Which polar bear will not benefit from natural selection? ______________________________________________
Identify the type of variation in the polar population. __________________________________________________
Who is the most fit in her environment? ____________________________________________________________
Predict how the gene pool (the alleles) will change over time. ___________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
2. Below is a series of pictures representing changes in a population of cacti over many generations.
Why would a deer be more likely to eat the left cactus than the right cactus? _______________________________
____________________________________________________________________________________________
In figure 3, the right cactus has flowers, but the cactus that has been eaten by the deer is too damaged to make
flowers. Figure 4 shows the situation several months later. What has happened? ____________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
Do you think that evolution by natural selection is occurring in this cactus population? Explain why or why not.
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
What adaptation seems to increase the fitness of the cacti on the right? How do you think this adaptation increases
the ability of cacti on the right to survive and reproduce?
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
3. There are two types of rabbits: those that strictly eat grass and those that strictly eat berries and flowers. A drought
occurs one year, and the plants have difficulty producing any extras (flowers, berries,
etc.).They can only try and keep themselves green. The rabbits have had babies all year
long but many are eaten by foxes or hawks. Due to the drought, many have starved to death.
Which rabbit will not benefit from natural selection? _________________________________________________
Identify the type of variation in the rabbit population. _________________________________________________
Who is the most fit in their environment? ___________________________________________________________
Predict how the gene pool (the alleles) will change over time. ___________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________
4. Bob believes that giraffes have long necks because they have stretched their necks to try and reach food that is high
in trees. Since the parent had stretched its neck, it passed the long neck on to its offspring. Ryan
believes that giraffes have long necks because the ones with long necks were able to reach the food, and
those with short necks could not and died. The long necked giraffes reproduced, and soon all of the
giraffes had long necks.
Who thinks like Lamarck? ___________________________________
Who thinks like Darwin? ____________________________________
Explain two potential environment factors that may have led to the change in the giraffee population.
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
______________________________________________________________________________________
5. A more complete definition of fitness is the ability to survive and produce offspring who can also survive and reproduce.
Below are descriptions of four male lions.
Name
George
Dwayne
Spot
Tyrone
Age at death
13 years
16 years
12 years
10 years
# cubs fathered
19
25
20
20
# cubs surviving to adulthood
15
14
14
19
Size
10 feet
8.5 feet
9 feet
9 feet
(Adapted from Michigan State University, Occasional Paper No. 91, Evolution by Natural Selection: A Teaching Module by Beth Bishop and Charles Anderson, 1986)
According to this definition of fitness, which lion would biologists consider the “fittest”? Explain why.__________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
Suppose that Tyrone had genes that he passed on to his cubs that helped his cubs to resist infections, so they were
more likely to survive to adulthood. Explain in some detail what would you expect to happen to the population of
lions over the next two thousand years? _____________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________