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Industrial Revolution | Genetic Changes | Natural Selection
Dark peppered moth. Image by Jerzy Strzelecki via Wikimedia Commons.
RS Edleston was an English naturalist who studied insects in the 1800s. In 1848 he recorded an unusual discovery in his journal. “Today I caught an almost totally black form of Biston betularia (peppered moth) near the centre of Manchester.” This is the first recorded sighting of a dark peppered moth.
What was rare in 1848 became common over the next fifty years. By 1900, the peppered moth populations in areas around English cities were as much as 98% dark moths. Scientists became curious why this was happening.
During that time, England was experiencing what is known as the Industrial Revolution. Factories were being built, and they ran by burning coal for fuel. The result was a dark smoke that covered the surrounding countryside. Trees that had been light and covered by lichens now were dark and bare. This clearly was having some impact on the moths. Scientists began to try to find out why.
Some thought the adults were changing their colors the same way the larvae could match the color of the twigs. Others thought the chemicals in the smoke darkened the moths.
Finally it was found that the color was genetic. Moths passed their color to the next generation. Eggs from light moths developed into light moths and dark moth eggs turned to dark adults. The dark color was caused by a mutation in the DNA of a single moth, and the mutated gene had been passed to all its offspring.
This explained why the moths were dark, but not why the dark moths were taking over. Did the dark moths have an advantage in the dark forests? If so, the change in the moths was a result of natural selection.
Natural selection was proposed by Charles Darwin to explain how new species evolve. All types of living things have small differences between the individuals in the species. If one of those differences allows the individual to live longer, they will likely have more offspring. As that trait is passed on, the population starts to look more like the successful individual. Over time, the species changes.
Oil processing plant in Estonia. Image by hannu via Wikimedia Commons.
In 1896, J. W. Tutt suggested that the peppered moths were an example of natural selection. He recognized that the camouflage of the light moth no longer worked in the dark forest. Dark moths live longer in a dark forest, so they had more time to breed.
All living things respond to natural selection. Over 100 other species of moth were observed to darken over time in polluted forests. Scientists call this effect industrial melanism. Natural selection is still at work in the peppered moth. In the last 50 years, most industrial countries have significantly reduced their pollution. As predicted by the theory, the number of dark moths are dropping as the forests become cleaner.
Natural selection in peppered moths has been extensively studied. To find out how, continue reading onto Dr. Kettlewell’ experiments.
- 1. ______________is a pattern of gradual change in the condition of something over time.
A) TraitB) ChickensC) TrendD) ResourcesE) Competition
- 2. _________is described as any condition that may influence the availability of resources (including weather, water temperature, predation, etc)
A) probabilityB) populationC) Natural SelectionD) Environmental PressuresE) resources
- 3. The number of individuals in any given area is known as the ___ .
A) UnagiB) populationC) variationD) competitionE) reproduction
- 4. The difference between individual organisms within a population in terms of how they look/behave is known as ______.
A) population.B) TrendC) TraitD) VariationE) probability
- 5. An interaction that occurs among organisms whenever two or more organisms require the same limited resource is called________.
A) PopulationB) Environmental PressureC) variationD) Natural SelectionE) competition
- 6. Which of the following statements best describes what will most likely occur to the moth populations in the image below?
A) The light moths will be captured by predators more easily than the dark moths, and the population of dark moths will rise.B) None of the answers listedC) The light moths will change their wing color to match that of the dark moths.D) The dark moths will be captured by predators more easily than the light moths, and the dark moths will probably go extinct.E) The light moths will be captured by predators more easily than the dark moths, and the population of light moths will rise.
- 7. READ THE TABLE CAREFULLY: What is the most likely explanation of the data shown below?
A) There has been a drought in the area that is affecting all life forms.B) The moths are living in an environment with light trees.C) The moths are living in an environment with dark trees.D) The population of natural predators of the moths has gotten smaller.E) All of the answers listed
- 8. READ THE GRAPHS CAREFULLY: The pair of population graphs below display the results of two different five-year hunting cycles, one on light trees and one on dark trees. The population of light-colored moths is shown by the light gray dots, and the population of dark moths is shown by the dark gray dots. How do these results demonstrate natural selection?
A) On light trees, individual moths tried to become lighter in color to match the tree background. On dark trees, individual moths tried to become darker in color.B) The moths that were the same color as their background were more likely to survive and reproduce. Over time, the populations of these well-adapted moths increased.C) The moth populations shown here demonstrate random fluctuations over time that are not explained by tree color.D) All of the answers listedE) Small particles of tree bark became embedded in the moth’s wings, causing the moths to become darker on the dark trees and lighter on the light trees. These acquired traits were then passed down to the next generation of moths, causing the populations to change color over time.
- 9. Suppose a certain species of insect lives in the lush green canopy (top of the trees) of the rain forest. Some of the insects are bright green in color, and some are bright yellow. Assume there is a natural predator of the insect in the area. What do you expect to happen to the populations of the green and the yellow insects over time?
A) The green insect population will increase and the yellow insect population will decrease.B) Both insect populations will increase over time.C) Both insect populations will remain constant over time.D) None of the answers listedE) The green insect population will decrease and the yellow insect population will increase.
- 10. Natural selection can be observed in predator populations as well as on prey. Let's suppose that over time, a forest's trees became covered in light colored lichen (making all of the trees lighter) and the proportion of light moths increased to nearly 100%. (0% dark moths) What will most likely happen to predator populations?
A) All of the answers listedB) Over time, birds with better eyesight will become more common.C) None of the answer listedD) Birds may change hunting strategies or seek other sources of food.E) Bird populations will decrease, at least for a while.
- 11. Biological evolution is the process by which populations of organisms change over time. How could natural selection lead to evolution?
A) Biological Evolution does not work through natural selection but rather on whole new species being born all at once.B) Biological Evolution only changes organisms that die off.C) Over many generations, physical adaptations that are found to be helpful/ are passed on will become "normal" on organisms that survive. These traits get passed on, natural selection continues, and over time, based on traits that are helpful, this process changes how that species looks and acts.D) None of the answers....and none of your business. OK, this one is not the answer.E) Natural Selection only works over a few years and a species can't change all that much.