Answer

Student Exploration: Natural Selection

Vocabulary: biological evolution, camouflage, Industrial Revolution, lichen, morph, natural selection, peppered moth

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

The peppered moth (Biston betularia) is a common moth found in Europe, Asia, and North America. It is commonly found in two forms, or morphs: a dark morph and a light, speckled morph. Birds are a frequent predator of the peppered moth.

Which morph do you think would be easier to see on a dark tree trunk? ____dark  morph

Which morph do you think would be easier to see on a light tree trunk? ____dark morph

Gizmo Warm-up

The Natural Selection Gizmo™ allows you to play the role of a bird feeding on peppered moths. The initial population of 40 moths is scattered over 20 tree trunks. Click on moths to capture them. Click the Next tree button (or the spacebar on your keyboard) to advance to the next tree.

Check that LIGHT TREES is selected. Click Play (), and hunt moths for one year.

How many dark moths did you capture? ___8____

How many light moths did you capture? ______0_

Camouflage is coloring or patterns that help an organism to blend in with the background. Which type of moth is better camouflaged on light bark? __light__________

If a forest contained mostly light-colored trees, which type of moth would you expect to be most common? ____light moth

Introduction: Before the 19^th century in England, the air was very clean. The bark on trees was usually light in color. Abundant lichens growing on tree trunks also lightened their appearance.

Question: How does the color of a peppered moth affect survival?

Predict: Over time, what will to happen to the populations of light and dark moths on light trees? _Over time the population of light moths will keep on increasing on light trees since they will not be easily spotted and eaten by predators; while, the population of dark moths will keep on declining since they will be easily spotted and eaten by predators.

Experiment: Click Play and hunt peppered moths on light tree trunks for five years. In each year, try to capture as many moths as you can. Note: You can use the spacebar on your keyboard to quickly advance to the next tree.

After 5 years, select the TABLE tab and record the percentages of each moth type. (Note: The table shows current populations of each moth, not the number of captured moths.)

Then click the GRAPH tab, click the camera icon on the upper right to take a snapshot of the graph of your 5 year totals. Paste the snapshot into the lab report in the space below:

Picture of Graph:

Analyze: What do your results show? __The results shows that the population of dark moths keeps on declining as they are predated on till they are completely eliminated from the area. In the third year the population of the dark moths had been eliminated. Conversely, the population of light moths kept on increasing as they were difficult to be spotted by predators. By the third year, the study area was being dominated by the light moths.

Apply: Which type of moth do you think was more common before the 19^th century, when most trees were light in color? _The light moth was common before the 19^th Century since three backs were light in color and not covered in soot.

Extend your thinking: What strategies did you use to hunt for moths? __Strategies that I employed in hunting for moths included spotting of moths using their color in contrast with the background color; while flying from one tree to the next in search of the next meal.

Introduction: The 19^th century was the time of the Industrial Revolution in England. Most of the new industries used coal for energy, and the air was polluted with black soot. In forests near factories, the soot coated trees and killed lichens. As a result, tree trunks became darker.

Question: How did air pollution affect moth populations?

Predict: Over time, what will to happen to the populations of light and dark moths on dark trees? _Light moths were easily spotting on dark tree trunk; while dark moths were difficult to spot. In that case, light moths were increasingly vulnerable and easily visualized by predators. Therefore, the population of light moths declined while that of dark moths thrived.

Experiment: Click Play and hunt peppered moths on dark tree trunks for five years. In each year, try to capture as many moths as you can.

When you are done, select the TABLE tab and record the percentages of each moth type.

      Then click the GRAPH tab, click the camera icon on the upper right to take a snapshot of the graph of your 5 year totals. Paste the snapshot into the lab report in the space below:

Picture of Graph:

Analyze: What do your results show? __The results show that on dark tree trunks the population of dark moths keeps on increasing while that of light moths keeps on declining with time till they are completely eliminated from the area.

Apply: Which type of moth do you think was more common during the 19^th century? Why?

___Dark moths were common during the 19^th Century since the dark tree trunks created better hiding sites for dark moths while exposing light moths. Therefore, light moths become more vulnerable for predation.

(Activity B continued on next page)
Activity B (continued from previous page)

Draw conclusions: Natural selection is the process by which favorable traits tend to increase in frequency over time. How does this experiment illustrate natural selection?

__This experiment helps to illustrate natural selection in that depending on the environmental conditions at different time vulnerability of the characteristics of a moth could change from a vulnerable characteristic to an advantageous characteristic and vice versa. Population of light moths thrived when the tree trunks were light while that of dark moths declined. On the other hand, the population of dark moths thrived on dark tree trunks while that of light moths declined with time. In addition, the experiment shows that environmental conditions may change with time and the changes may favor a previously disadvantage trait while disadvantaging a previously disadvantaged trait.

Think and discuss: Did the changes you observed in the moth populations result from individual moths changing colors? Or did they occur because the best-hidden moths survived and reproduced, passing on their colors to their offspring? Explain your answer.

_The best-hidden moths survived and reproduced, passing their colors to the offspring. This is because on light tree trunks the percentage population of light moths kept on increasing while that of black moths declined. Light moths were better-hidden far more than dark moths on light tree trunks. Similarly, on dark tree trunks population of dark moths kept on increasing while that of light moths declined. Dark moths were better hidden that the light moths on dark tree trunks.

Extend your thinking: Biological evolution is the process by which populations of organisms change over time. How could natural selection lead to evolution? If possible, discuss your answer with your classmates and teacher.

___Natural selection can lead to biological evolution since organisms that possess certain advantageous characteristics at a given point in time can be favored by environmental demands at that point in time. Such organisms can then survive to the reproductive age and reproduce. With time, given that environmental conditions and demands will remain constant, population of organism with advantageous characteristics will thrive and increase while organisms with disadvantageous characteristics will be selected against; thus, decline with time.