Biology Standard 2B
Natural Selection
Scenarios
Textbook:
Biology: The Dynamics of Life. 2002.
Chapter 15.1 (pps. 400-404)
Name ______________________
Period: _____
Scenario #1
Every summer it seems like my house is invaded with ants. I usually go to Home Depot and buy the strongest pesticide I can
get. I usually buy 2-3 bottles and make sure that I put it around the perimeter of my yard, my house and in the areas I have
recently seen the ants. Initially, I noticed that many of the ants were dying within hours of coming in contact with the
pesticide. A few days later I noticed some "zombie like" ants walking around my home but only in groups of twos and
threes. About 2 weeks after I laid down all of the pesticide, I noticed a few more ants, they seemed a little smaller and when
I crushed them under my thumb, I didn't notice the pop/crunch that I usually feel when I kill them. By the end of the
summer, I notice that the ants seem immune to the pesticide as they have begun to invade my house again, it seems like the
pesticide is having some effect on the ants, but many are surviving. I am thinking of heading back to Home Depot to try
another type of pesticide.
Based on the scenario above--identify the four steps of natural selection:
1. Organisms produce more offspring than can survive:
2. Variation exists in the population:
3. Beneficial variations help organisms survive:
4. Overtime, beneficial variations of will be passed on increase in the next generation:
Identify the mode of Natural Selection that is occurring: ___________________________________
Draw a graph to show the mode of natural selection (label the variations):
Is the beneficial adaptation a structural (anatomical), physiological or behavioral adaptation? Explain:
Is the adaptation driven by an abiotic or biotic force? ____________________________________
Explain your answer:
Scenario #2
Sexual dimorphism is when there is a phenotypic difference between the male and female sexes. Usually we equate beauty
with feminine--but that is not always the case, especially with birds. A female peacock has brown feather that do not drag
behind her--she needs to blend into her environment and make swift movements to protect her young. The male peacock
however has evolved a different strategy. According to experts, female peacocks choose mates based on the color of the
feathers and the overall physical prowess of the animal. The brightness of the plumage might signal to the female that the
male has high-quality genes. This would make him ideal for reproduction; therefore the males with the brightest colors and
displays are often selected. In reality, not all males have bright, large tails, and this was especially true thousands of years
ago. As females began to select the brightest male for sexual partners; the peacocks will less impressive tails were less likely
to mate and reproduce. However there is a trade-off, if the peacocks' feathers were too long, too cumbersome and too
flashy, it would attract predators...basically if you weren't sexy enough, you wouldn't attract a mate, but if you were too
sexy and flashy, you would attract more mates and more predators.
Based on the scenario above--identify the four steps of natural selection:
1. Organisms produce more offspring than can survive:
2. Variation exists in the population:
3. Beneficial variations help organisms survive:
4. Overtime, beneficial variations of will be passed on increase in the next generation:
Identify the mode of Natural Selection that is occurring: ___________________________________
Draw a graph to show the mode of natural selection (label the variations):
Is the beneficial adaptation a structural (anatomical), physiological or behavioral adaptation? Explain:
Is the adaptation driven by an abiotic or biotic force? ____________________________________
Explain your answer:
Scenario #3
When you think of the American Southwest, you probably think of cacti both big and small. Well if you were to visit the
American Southwest today, you might be disappointed with the lack of variation among cactus species--especially right off
the major highways. In 1926, Route 66 was the nation's first major highway to allow visitors to visit the southwest. Like
many tourists--they wanted to take home a memento of their travels. Many people would pull over and begin looking for
their own living souvenir. Since many of the tourists did not have the necessary tools to extract a spiny cactus out of the
soil--they usually had to make a conscious decision about what type of cactus they should dig up. The cacti with too many
spines were seen as too difficult to dig out and the visitors didn't likely have gloves to protect their hands. The cacti with too
few spines were seen as "homely" and were often overlooked. Therefore, the tourists found a cactus that was between
these two extremes. Over the last century, the phenotypic variation within these small cacti has changed (at least in areas
accessible by these highways.)
Based on the scenario above--identify the four steps of natural selection:
1. Organisms produce more offspring than can survive:
2. Variation exists in the population:
3. Beneficial variations help organisms survive:
4. Overtime, beneficial variations of will be passed on increase in the next generation:
Identify the mode of Natural Selection that is occurring: ___________________________________
Draw a graph to show the mode of natural selection (label the variations):
Is the beneficial adaptation a structural (anatomical), physiological or behavioral adaptation? Explain:
Is the adaptation driven by an abiotic or biotic force? ____________________________________
Explain your answer:
Scenario #4
The Amish is closed community of Christians who believe in simple living, plain dress and are reluctant to adopt modern
technology. In the early 1800's a group of approximately 200 Amish immigrated to Pennsylvania from Switzerland. Today
over 200,000 Amish members live in the United States. They are considered a closed genetic community because it is rare
for woman or men to marry into the Amish community. Therefore, the incidence of certain genetic disorders are higher in
the Amish community. Ellis-van Creveld syndrome is a form of dwarfism that has a high prevalence of polydactyl
deformities. This rare syndrome is many times more common in the Amish population than in the American population at
large and the mutated gene that causes this syndrome can be traced back to Samuel King, when he joined the Amish
community in the 1700's. Even through this type of dwarfism has no benefit--the numbers of new cases continues to rise at
an alarming rate in the Amish community.
Based on the scenario above--why is natural selection not occurring?
Is the adaptation a structural (anatomical), physiological or behavioral adaptation? Explain:
Is the adaptation driven by an abiotic or biotic force? ____________________________________
Explain your answer:
Scenario #5
About 10,000,000 years ago, scientists believe humans started to branch off from their gorilla ancestors. To help scientists
understand when we started to make the transition from ape to human, they began to look at the evolution of the human
louse. By looking at the DNA of head lice and body lice; scientists have determined that they evolved from a common
ancestor. But what caused them to diverge into two different species in the first place? Well we know that one of the
physical differences between humans and their ape counterparts is body hair. Hair keeps us warm; the loss of hair would
eventually require humans to seek clothing for heat/warmth. During this time when humans were first beginning to wear
clothing; some opportunistic lice were able to use the habitat of the clothing to find a new niche. Read below, to see how
head and body lice differ:
Head Lice: Live on the human scalp; drink human blood; will die w/o blood in 1 day; non-deadly
Body Lice: Live in clothes, bedding; drink human blood; will die w/o blood in 3-5 days; deadly
(carry diseases)
Notice that body lice can live longer without blood; their ancestors were most likely able to live without feeding for longer
periods of time; allowing them to move from the head to the clothing and remain alive. Over time, the lice that could adapt
to living in the clothes and possibly eating less frequently diverged away from head lice which relied on daily blood feedings.
Scientists determined from DNA evidence that the head and body louse diverged 170,000 years ago; that means in order for
lice to adapt to living on clothes and bedding; we must have been using clothes or bedding for at least that long.
Based on the scenario above--identify the four steps of natural selection that led to body lice:
1. Organisms produce more offspring than can survive:
2. Variation exists in the population:
3. Beneficial variations help organisms survive:
4. Overtime, beneficial variations of will be passed on increase in the next generation:
Identify the mode of Natural Selection that is occurring: ___________________________________
Draw a graph to show the mode of natural selection (label the variations):
Is the beneficial adaptation a structural (anatomical), physiological or behavioral adaptation? Explain:
Is the adaptation driven by an abiotic or biotic force? ____________________________________
Explain your answer:
Scenario #6
Poplar trees are fast growing and are seen by many as a sustainable resource for lumbar. In Europe, these trees which grow
naturally in the forests and vary by region and climate. On average these trees can grow up to 16 feet in a single growing
season. Like many trees, Poplars grow best in direct sunlight. This shouldn't be a problem as they seem to grow so quickly.
However, the European Poplar is currently being affected by a fungus. About 1/3 of the trees do not show any fungal
infection, about 1/3 has a mild infection that is showing some reductions in growth between 5-25% and the final 1/3 of
trees are infested with the fungus reducing their growth by 50%; which over 2-3 growing seasons, this may prevent the tree
from receiving direct sunlight and dying a pre-mature death.
Based on the scenario above--identify the four steps of natural selection:
1. Organisms produce more offspring than can survive:
2. Variation exists in the population:
3. Beneficial variations help organisms survive:
4. Overtime, beneficial variations of will be passed on increase in the next generation:
Identify the mode of Natural Selection that is occurring: ___________________________________
Draw a graph to show the mode of natural selection (label the variations):
Is the beneficial adaptation a structural (anatomical), physiological or behavioral adaptation? Explain:
Is the adaptation driven by an abiotic or biotic force? ____________________________________
Explain your answer:
Scenario #7
In the seas of southeast Asia, a fisherman has been using the same size nets as his ancestors have been using for hundreds of
years. The nets are weaved so that they target a specific size fish--this will catch medium and large sized fish--allowing the
smaller fish to pass through, grow up and reproduce. This practice done in a sustainable way allows the oceans to replenish
their stocks. However, in the last 75 years, the industrialization of fishing world-wide has depleted the ocean stocks of
large fish. In comparison to the size of fish available in the middle of the 20th century--the average size of fish has decreased
between 50-88% depending on the species. In order to ensure people do not starve, fishermen in southeast Asia and on the
industrial boats have had to change the size of their nets, catching smaller fish even before they have reproduced.
Based on the scenario above--identify the four steps of natural selection:
1. Organisms produce more offspring than can survive:
2. Variation exists in the population:
3. Beneficial variations help organisms survive:
4. Overtime, beneficial variations of will be passed on increase in the next generation:
Identify the mode of Natural Selection that is occurring: ___________________________________
Draw a graph to show the mode of natural selection (label the variations):
Is the beneficial adaptation a structural (anatomical), physiological or behavioral adaptation? Explain:
Is the adaptation driven by an abiotic or biotic force? ____________________________________
Explain your answer:
Scenario #8
In the Pacific, near New Guinea, there are small islands where there is no human settlement. Here a beautiful bird named
the Louisiade White-Eye lives. The birds range in color from white with traces of green, to bright yellow and neon green.
The green feathers are a result of the dominant gene, while the yellow are an expression of a recessive gene. A typhoon
swept through the islands killing most of the birds and their new hatchlings from the islands. A naturalist was sent to the
islands to determine how the population has recovered in the five years since the typhoon. They reported that the numbers
of Louisiade White-Eyes is over 500 but they are all yellow--no green birds were seen.
Why is natural selection not occurring in this population?
Scenario #9
The age a woman can have a child usually ranges from their teens to late forties. If a woman has a child too young, there
may be complications with the delivery if the woman has an underdeveloped pelvic region. If a woman waits too long to
have a baby, the chances of having a child with genetic disorders or infertility problems increases. Therefore women in their
twenties and early thirties statistically have a lower risk pregnancy.
Based on the scenario above--identify the four steps of natural selection:
1. Organisms produce more offspring than can survive:
2. Variation exists in the population:
3. Beneficial variations help organisms survive:
4. Overtime, beneficial variations of will be passed on increase in the next generation:
Identify the mode of Natural Selection that is occurring: ___________________________________
Draw a graph to show the mode of natural selection (label the variations):
Is the beneficial adaptation a structural (anatomical), physiological or behavioral adaptation? Explain:
Is the adaptation driven by an abiotic or biotic force? ____________________________________
Explain your answer:
Scenario #10
A group of nomadic people head towards the North Pole. The range in height from short, medium and tall. Once they have
settled in, they soon realize that it's freezing. To help keep warm, the nomads begin to dig holes in the snow to build ice
houses. The snow is hard and only small holes can be dug. Overtime, the smaller nomads were able to survive because they
were able to brave the elements in the snow houses. While some taller nomads are still around, the small "elvish-sized"
nomads greatly out-number them--have to "help" the taller nomads survive.
Based on the scenario above--identify the four steps of natural selection:
1. Organisms produce more offspring than can survive:
2. Variation exists in the population:
3. Beneficial variations help organisms survive:
4. Overtime, beneficial variations of will be passed on increase in the next generation:
Identify the mode of Natural Selection that is occurring: ___________________________________
Draw a graph to show the mode of natural selection (label the variations):
Is the beneficial adaptation a structural (anatomical), physiological or behavioral adaptation? Explain:
Is the adaptation driven by an abiotic or biotic force? ____________________________________
Explain your answer:
Scenario #11
A population of monkey lived in a large forest surrounded by canyons, they were omnivores, mostly eating berries, grass
and vegetable roots but supplemented their diet with small mammals when needed. The average size of these monkey's
ranged between 8 and 12 pounds. A large earthquake separated these monkeys from their natural environment, leaving a
river that no monkey could cross. Unfortunately the monkeys were separated from their natural food supply, they had few
plants to eat and had to eat more mammals in order to survive--while they still ate like omnivores--they were becoming
more carnivorous. The ability to properly digest raw meal varies greatly within the monkey population, it depends on if the
monkey has a functioning appendix. A hundred thousand years later, the monkey's ranged in size between 10 and 19
pounds.
Based on the scenario above--identify the four steps of natural selection:
1. Organisms produce more offspring than can survive:
2. Variation exists in the population:
3. Beneficial variations help organisms survive:
4. Overtime, beneficial variations of will be passed on increase in the next generation:
Identify the mode of Natural Selection that is occurring: ___________________________________
Draw a graph to show the mode of natural selection (label the variations):
Is the beneficial adaptation a structural (anatomical), physiological or behavioral adaptation? Explain:
Is the adaptation driven by an abiotic or biotic force? ____________________________________
Explain your answer:
Scenario #12
Within a forest there are four different colors of beetles (they are all the same species): black, green, red and yellow. The
crow is a natural predator to the beetles. It seems like the crow eats all of the bugs equally except the yellow beetles. The
yellow beetles seem to have a lower rate of predation. Almost 5 times less than any other color. It seems like the yellow
beetle must have some advantage over the other colors. When scientists looked closer at the situation they realized that the
color yellow was connected to the crow's eyesight. Crow's are blind to a specific color of yellow--a shade that over 80% of
the yellow beetles posses. This accounted for their lower rates of predation.
Based on the scenario above--identify the four steps of natural selection:
1. Organisms produce more offspring than can survive:
2. Variation exists in the population:
3. Beneficial variations help organisms survive:
4. Overtime, beneficial variations of will be passed on increase in the next generation:
Identify the mode of Natural Selection that is occurring: ___________________________________
Draw a graph to show the mode of natural selection (label the variations):
Is the beneficial adaptation a structural (anatomical), physiological or behavioral adaptation? Explain:
Is the adaptation driven by an abiotic or biotic force? ____________________________________
Explain your answer:
Scenario #13
A black widow spider is capable of producing hundreds of offspring at one time. Black widow spiders catch their prey using
webs. The strength of the web varies by the spider who spins it. The stronger the web, the more likely the prey will not be
able to escape the web. Therefore spiders who have the ability to spin stronger nets, are more likely to catch prey, which
increases their odd of surviving to reproduce.
Based on the scenario above--identify the four steps of natural selection:
1. Organisms produce more offspring than can survive:
2. Variation exists in the population:
3. Beneficial variations help organisms survive:
4. Overtime, beneficial variations of will be passed on increase in the next generation:
Identify the mode of Natural Selection that is occurring: ___________________________________
Draw a graph to show the mode of natural selection (label the variations):
Is the beneficial adaptation a structural (anatomical), physiological or behavioral adaptation? Explain:
Is the adaptation driven by an abiotic or biotic force? ____________________________________
Explain your answer: