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.
Industrial Revolution
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.
Genetic Changes
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
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.
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.
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Play the game twice. Once in the light forest and once in the dark forest. It will allow you to play each game for 1 minute. When the game is over. It will tell you the percent of light moths left in the population and the percentage of dark moths left in the population. After each game record your data in the table below. https://askabiologist.asu.edu/peppered-moths-game/play.html
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Science requires that theories be tested to see if they are supported by evidence. During the 1950’s, Henry Bernard Davis Kettlewell ran a series of experiments and field studies to find out if natural selection had actually caused the rise of the dark peppered moth.
Scientific question: Why did most moths in Manchester have dark, peppered coloring?
Experiment: To directly study bird predation on the moths, Dr. Kettlewell placed light and dark moths on the trunks of trees where he could observe them. He recorded the times a bird found the moth.
He found that on dark tree trunks, birds were twice as likely to eat a light moth as a dark moth. The same birds would find the dark moth twice as often if the bark on the tree was light. This supported the idea that dark moths had a survival advantage in a dark forest.
In this experiment, what is the independent variable
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In his experiment, what is the dependent variable
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Make a claim to answer this question:
Scientific question: Why did most moths in Manchester have dark, peppered coloring?
****Reminder as per box one Claim = INSERT SPECIES HERE has INSERTT TRAIT HERE because of INSERT ENVIRONMENTAL FACTOR HERE .....need an environmenntal factor because we are trying to prove, through these case studies that, natural selection (selective environmental factors) cause adaptations.
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Provide evidence to support your claim above (for evidence please use the data you collected in the simulation from question 1.
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Provide a reasoning to connect scientific theory and evidence to your claim. In 6 numbered steps write your reasoning. (Use the boxes below as a template for what to write on each step for a fully complete answer----remember you are not copying what is in the boxes, you are using it as a framework to apply to this scenario).
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In the moth scenario in the previous questions, what was the adaptation that arose in moths as a result of natural selection?
Case Study 3: Antibiotic Resistance
How Do Antibiotics Work?
Antibiotics are medicines capable of killing or preventing the reproduction of microbes, specifically bacteria. An
antibiotic is a substance that is toxic to specific bacteria. Antibiotics can affect bacteria in a variety of ways. For
example, they may damage one of the proteins that convert glucose to energy, break down proteins that
make up the cell wall or membrane, or they may preventproteins needed for reproduction from being formed, as well as many other ways.
The Evolution of Microbes: Antibiotic Resistance
The overexposure of microbes to antibiotics has provided environmental conditions in which the microbes must change, or evolve, to survive the use of specific antibiotics. How does a microbe evolve? Evolution is driven by environmental pressure. An organism that is under pressure to survive must change or risk becoming extinct. Mutation is the mechanism of evolution. Microbes with mutations that are resistant, or immune, to an antibiotic will survive to reproduce, and they will pass the mutation to their offspring.
As an example, Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common and dangerous antibiotic-resistant organisms. Staphylococcus aureus is a common bacterium found on human skin. When the skin is broken open, it can cause a Staph infection. Methicillin is an antibiotic that blocks the protein responsible for creating a substance that forms the cell wall surrounding S. aureus. When exposed to methicillin, normal S. aureus is unable to form its cell wall, which causes cell death. MRSA has a mutation of the protein, and the methicillin can no longer block it because its shape has changed. This effectively prevents methicillin from fighting against MRSA.
Scientific question: What causes antibiotic resistant bacterial strains?
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Collect data in the chart attached using the image provided.
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The above data experiment was performed on agar in petri dishes in a science lab.
Scientific question: What causes antibiotic resistant bacterial strains?
In this experiment, what is the independent variable
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The above data experiment was performed on agar in petri dishes in a science lab.
Scientific question: What causes antibiotic resistant bacterial strains?
In this experiment, what is the dependent variable
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Make a claim to answer the following question:
Scientific question: What causes antibiotic resistant bacterial strains?
****Reminder as per box one Claim = INSERT SPECIES HERE has INSERTT TRAIT HERE because of INSERT ENVIRONMENTAL FACTOR HERE .....need an environmenntal factor because we are trying to prove, through these case studies that, natural selection (selective environmental factors) cause adaptations.
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Provide evidence to support your claim above (for evidence please use the data you collected in the table from question 8.
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Provide a reasoning to connect scientific theory and evidence to your claim. In 6 numbered steps write your reasoning. (Use the boxes below as a template for what to write on each step for a fully complete reasoning----remember you are not copying what is in the boxes, you are using it as a framework to apply to this scenario).
