Lab: Natural Selection Vocabulary : Phenotype Genotype Survival

Name: ______Date:______Methods Natural Selection: 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. Which prey will survive? 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. 1.On the back, make a bar graph 4. Calculate the number of surviving prey for each color. showing the changes in the popula- 5. Calculate the prey’s reproductive success by adding 1 offspring for each sur- tions from start to finish. viving prey (matching color!!). Add the offspring to the surviving popula- tion of prey on the cloth. This will be your new population in the next genera- tion. 2. Which “prey” survive and repro- 6. Repeat steps 2 – 4 six more times for a total of seven generations. duce? Why? Note – do not add any new offspring after the 2nd generation. ______COLORS: ______First Generation 10 10 10 ______Killed prey (removed from cloth) Surviving prey (remaining on cloth) 3. If the fabric had been white, Number of offspring would your results have been differ- Replace one for every “SURVIVING” BEAD ent? Explain why or why not. Second generation starting number ______Killed prey (removed from cloth) ______Surviving prey (remaining on cloth) ______Number of offspring ______Replace one for every “SURVIVING” BEAD

4. Describe how your results illus- Third generation starting number—Stop trate natural selection. 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 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 cer- tain traits or adaptations have greater survival and reproduction than individuals who lack those traits or ad- aptations. 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 stabiliz- ing 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 cit- ies. 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 sur- faces, the dark colored ones were harder to spot by birds who ate them and, subsequently, they more often lived long enough to re- produce. Over generations, the environment continued to favor darker moths. As a result, they progressively became more com- mon. 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 Liver- pool. 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-

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