Evolution and Selection

What mechanisms lead to changes in the diversity of species on Earth?

Why?
People make choices by selecting options they like best. The natural world also “selects” (although not as
a conscious decision) when environmental conditions allow organisms with a particular genetic trait to
live healthier lives than other organisms. In this activity, we will explore how selection affects populations
over time.

Model 1 – Desktop Swab Results

E. coli bacterial
variants from culture
Variant P
Variant Q
Variant R
Varient S

E. coli culture
from swab
of desktop

E. coli colonies on E. coli colonies on

growth medium growth medium
without triclosan with triclosan

1. What is the source of the bacteria in the culture tube in Model 1?

From a swab of desktop

2. How many genetic variants of E.coli were present in the culture from the initial swab?

4
3. What variants of E.coli are found on the dish grown without triclosan?
4
4. Refer to the dish in Model 1 with the medium that included triclosan.
a. What variants of E.coli are found on the dish grown with triclosan?
1
b. What likely happened to the other variants of E.coli on the dish with the medium containing
triclosan?
They were not able to survive and reproduce.

Evolution and Selection 1

 5. Based on its effect on E.coli, why is triclosan used as a cleaning agent?

it’s ability to effectively eliminate all of the bacteria

6. Suppose the desktop swabbed earlier was cleaned with a solution containing triclosan. Would
living E.coli remain? Support your answer.

No because they would be killed, and not able to reproduce

7. Suppose the desktop was swabbed again after cleaning it with triclosan over a 9-month school
year. When the sample was cultured only variant S was seen.
a. What characteristic does the variant S bacteria have that allows it to remain on the desktop
even after several months of treatment with triclosan?
it shows immunity to a cleaning agent with triclosan

b. Is it likely that the bacteria in the new swab were on the desk 9-months ago, or are they off-
spring of the original bacteria?
It is likely offspring of the original bacteria. This I because these bacterial are immune
against triclosan, and these bacteria might’ve survived.
c. Propose an explanation for the presence of only variant S on the desktop after so much time.
Variant S might have a tiny bit of the triclosan, and learned how to defend itself against it.
Kind of like how the human body protects itself against the Covid-19 Disease.

Read This!
Populations of most living organisms exhibit genetic diversity among individuals. Certain traits in a
population give some organisms a greater chance of survival than individuals that lack these traits. Because
these traits tend to increase the chance of survival, these individuals may produce more offspring that will
also have the trait that favors survival. Over time, the number of individuals within the population pos-
sessing the favorable trait increases while the number of offspring with the favorable trait decreases.

2 POGIL™ Activities for High School Biology

Model 2 – Color Variations in Moths in Great Britain
Peppered Moth Frequency
100

It
90
Percentage of Moths Captured

80

70

60

50

40

30

20

10 Light moths
Dark moths
0
1800 1850 1900 1950 2000

Years

8. Refer to the graph of Peppered Moth Frequency in Model 2.

a. Which moth color was more prevalent before 1850?
Light Moths
b. Which color was more prevalent between 1900 and 1950?
Dark Moths
9. Describe the change in the percentage of light-colored moths and dark-colored moths between
1850 and 1900.
There might’ve been an outbreak in dark colored trees, for some environmental reason like soot being
launched into the atmosphere, and the dark colored moths, were able to survive so well.
10. Describe the change in the percentage of light-colored moths and dark-colored moths between
1950 and 2000.
The population of the dark color moths had drastically decreased and the opposite is true
for the population of the light colored moths.
11. During the Industrial Revolution through the mid-20th century, factories and power plants,
which burned coal, produced large quantities of soot and smog. Near industrialized areas, black
powder covered surfaces, including the moth habitat.
a. Which color moth would have a better chance of surviving predation (better camoflage to
hide from predators) on this dark surface?
Dark color moths
b. How does this help explain the change in the colors of the moth population shown in Model 2?

the trees would change their color to better hide inside of the smog, and so the
Moths would follow suit.

Evolution and Selection 3

 12. Clean Air Acts were passed by governments of industrialized nations beginning in the mid-
1950s. Use this information to explain why the color of the moth population shifted again.

the smog would’ve lifted, giving the moths another chance to become lighter colored.

Model 3 – Natural vs. Artificial Selection

§ Dog

Gray Wolf

Red Wolf

Coyote

§ – Artificial selection

13. Model 3 traces the lineage of what organisms?

Wolfs
14. How does Model 3 indicate that all three types of organisms came from a common ancestor?
They all have similar shapes and functions
15. According to Model 3, wolves (gray and red) are more closely related to what other group—dogs or
coyotes? Explain your answer.
Coyotes. This is because they are more un-trained, and dogs are an artificial selection.

16. Think about the characteristics of the organisms above.

a. What are some differences that you note between wolves and dogs?
Dogs range in color and shape, where wolves stay relatively the same.

b. What similarities can you identify?

They both have snouts, and they both can

walk on 4 feet.

4 POGIL™ Activities for High School Biology

 17. Modern domesticated dogs arose from wolves through selective breeding by humans.
a. What traits might humans have selected in the common ancestor of dogs and wolves that
would account for the differences between dogs and wolves?
Ones that are more caring to humans, and ones that can protect them.
b. According to Model 3, what is the name of this type of selection?
Artificial Selection

Read This!
The events that lead to changes in groups of organisms are called selection by evolutionary biologists.
Charles Darwin (1809–1882) is the person credited with carefully outlining how various changes in
populations of organisms might occur through time. He called this process natural selection. Humans
participate in selection through selective breeding of plants and animals. This is referred to as artificial
selection.
18. Is the selection that led to the development of wolves and coyotes an example of natural selection
or artificial selection? Explain your choice.
Natural because there was no selective breading, and it would’ve taken many, many centuries to create
another species, comparatively to the artificial that would’ve taken weeks

19. Refer to Model 1. Is the selection leading to changes in the E. coli variants natural or artificial
selection? Explain your choice.
Artificial because you are interfering with the other bacterias from forming, where you
are killing them!
20. Two differences between red and gray wolves is their color and size. What environmental condi-
tions might have resulted in selection for red wolves and gray wolves?

Maybe the gray wolves live in a soot covered area, and the red wolves could live near a
volcano (or mars, I don’t know any places that are red)
21. Refer to Model 2. Is the selection of moths that blend in to their environment an example of
natural or artificial selection? Explain your choice.

Natural because the moth’s evolutionary chance comes with changes in the environment.

Evolution and Selection 5

Extension Questions
22. For the past 10 to 25 years, farmers have planted crop seeds that have been genetically modified
to withstand treatment with a common weed killer called Roundup®. This allows the farmers to
spray their fields to get rid of weeds without harming their crops. Recently, more and more farm-
ers have discovered that their fields have Roundup-resistant pigweed growing along with their
crop. Use what you’ve learned in this activity to explain how this came about.
The pigweed would be exposed to the Roundup, and this caused them to make
mutations and change their DNA sequence, and those who were able to survive,
were able to reproduce and pass down those genes that kept them alive.

23. Many popular products from hand soap to clothing advertise that they have antibacterial quali-
ties. Most microbiologists recommend against their routine use in our daily lives. How can you
explain this using your knowledge from this activity?

Most likely, these antibacterial qualities can cause people to be exposed to bacteria and
this would make them susceptible to diseases and more.

6 POGIL™ Activities for High School Biology