Lab: Natural Selection
Vocabulary : Phenotype
Genotype
Survival
Name: ___________________________________Date:_____________
Methods Natural Selection:
Which prey will survive?
1.On the back, make a bar graph
showing the changes in the populations from start to finish.
2. Which “prey” survive and reproduce? Why?
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3. If the fabric had been white,
would your results have been different? Explain why or why not.
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4. Describe how your results illustrate natural selection.
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1. Working in groups of six, get 20 each of three different colored items.
2. Establish the population by placing ten of each item on the fabric.
2. One student is the predator. The predator searches the cloth and removes as
many prey as possible in 5 seconds using the provided tool.
3. Count the number of each prey color removed and record it in Table 1.
4. Calculate the number of surviving prey for each color.
5. Calculate the prey’s reproductive success by adding 1 offspring for each surviving prey (matching color!!). Add the offspring to the surviving population of prey on the cloth. This will be your new population in the next generation.
6. Repeat steps 2 – 4 six more times for a total of seven generations.
Note – do not add any new offspring after the 2nd generation.
COLORS:
First Generation
Killed prey (removed from cloth)
Surviving prey (remaining on cloth)
Number of offspring
Replace one for every “SURVIVING” BEAD
Second generation starting number
Killed prey (removed from cloth)
Surviving prey (remaining on cloth)
Number of offspring
Replace one for every “SURVIVING” BEAD
Third generation starting number—Stop
Adding Offspring
Killed prey (removed from cloth)
Surviving prey (remaining on cloth)
Fourth generation starting number
Killed prey (removed from cloth)
Surviving prey (remaining on cloth)
Fifth generation starting number
Killed prey (removed from cloth)
Surviving prey (remaining on cloth)
Sixth generation starting number
Killed prey (removed from cloth)
Surviving prey (remaining on cloth)
Final generation total number
10
10
10
Introduction:
Charles Darwin is universally associated with evolutionary theory. His major contribution was to describe the
primary mechanism by which it worked: natural selection. Darwin said that it is the forces of nature that select
species to survive that are best adapted to the environment. These species in turn produce offspring and their
numbers increase. Darwin proposed four tenets by which natural selection operates:
1. Genetic variation.
2. Overproduction of offspring.
3. Struggle for existance.
4. Differential survival and reproduction.
We know from the fossil record that species evolve over time. Darwin argued that the primary mechanism of
evolutionary change is the process of natural selection. Natural selection occurs because individuals with certain traits or adaptations have greater survival and reproduction than individuals who lack those traits or adaptations. Selection that favors one extreme characteristic over the other is known as directional selection.
When selection favors an intermediate characteristic rather than one of the extremes, it is known as stabilizing selection. Selection that operates against the intermediate characteristic and favors the extremes is called
disruptive selection.
An example of evolution resulting from natural selection was discovered among "peppered" moths living near English industrial cities. These insects have varieties that vary in wing and body coloration from light to dark. During the 19th century, sooty smoke from
coal burning furnaces killed the lichen on trees and darkened the bark. When moths landed on these trees and other blackened surfaces, the dark colored ones were harder to spot by birds who ate them and, subsequently, they more often lived long enough to reproduce. Over generations, the environment continued to favor darker moths. As a result, they progressively became more common. By 1895, 98% of the moths in the vicinity of English cities like Manchester were mostly black. Since the 1950's, air pollution
controls have significantly reduced the amount of heavy particulate air pollutants reaching the trees, buildings, and other objects in the
environment. As a result, lichen has grown back, making trees lighter in color. In addition, once blackened buildings were cleaned
making them lighter in color. Now, natural selection favors lighter moth varieties so they have become the most common. This trend
has been well documented by field studies undertaken between 1959 and 1995 by Sir Cyril Clarke from the University of Liverpool. The same pattern of moth wing color evolutionary change in response to increased and later decreased air pollution has been
carefully documented by other researchers for the countryside around Detroit, Michigan. While it is abundantly clear that there has
been an evolution in peppered moth coloration due to the advantage of camouflage over the last two centuries, it is important to keep
in mind that this story of natural selection in action is incomplete. There may have been addi-
http://anthro.palomar.edu/evolve/evolve_2.htm