MS-LS4-6: Natural Selection Process

MS-LS4-6
Natural Selection Process

Middle School

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Learning Objectives

• Define natural selection and the conditions required for it to occur.

• Explain how environmental conditions change the traits in a population over time.

• Use graphs and data to explain how natural selection affects a population.

• Describe how helpful traits become more common and other traits become less common.

• Understand natural selection is based on probability and cause-and-effect relationships.

Key Vocabulary

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Natural Selection

A process where organisms with beneficial traits are more likely to survive and reproduce successfully.

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Adaptation

A trait that develops from a mutation, which helps an organism survive in its environment.

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Mutation

A random change that occurs in an organism's DNA sequence, which can result in new traits.

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Inherited Trait

A specific characteristic that is passed down from parents to their offspring through their genes.

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Distribution of Traits

The frequency of different traits that are found within a given population of a species.

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Population

A group of individuals of the same species that live together in the same area.

The Process of Natural Selection

• Adaptations are helpful traits that arise from random changes in an organism's DNA.

• Organisms with beneficial adaptations are more likely to survive and pass them on.

• This process, natural selection, requires variation, inheritance, and different survival rates.

Multiple Choice

According to the principles of natural selection, which three things are required for the process to occur in a population?

• Random changes, DNA, and a stable environment

• Variation, inheritance, and different survival rates

• Adaptations, learned behaviors, and reproduction

• Helpful traits, random changes, and a single organism

Multiple Choice

What is the primary role of a beneficial adaptation within the process of natural selection?

• They are developed intentionally by an organism to meet a need.

• They increase the likelihood that an organism will survive and pass on its DNA.

• They guarantee that an individual organism will live a long life.

• They cause random changes in an organism's DNA to stop happening.

Multiple Choice

A population of rabbits has variation in fur thickness due to random DNA changes. If the climate in their habitat slowly becomes much warmer, what is the most likely outcome?

• The entire rabbit population will be unable to survive the change.

• The rabbits will immediately develop thicker fur to adapt to the cold.

• The trait for thin fur will likely become more common in the population over many generations.

• Individual rabbits will change their fur thickness back and forth each year.

Natural Selection in Action

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Resistant Bacteria

• Some Salmonella bacteria developed mutations that made them resistant to antibiotics.

• Antibiotics killed non-resistant bacteria, so resistant ones survived and reproduced.

• They passed the resistance trait to their offspring, making it more common.

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Prairie Larkeys

• When larkeys moved to prairies, the long-legged trait was more suitable.

• Larkeys with long legs were better at surviving and having more young ones.

• Over generations, the long-legged trait became more common in the population.

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Blue Moon Butterflies

• A genetic mutation helped some male butterflies survive a deadly bacterial infection.

• These resistant males were able to mate and pass on the trait.

• The resistance spread quickly, allowing the butterfly population to recover rapidly.

Multiple Choice

What is the common outcome in the examples of the bacteria, larkeys, and butterflies?

• A beneficial trait becomes more common in the population over time.

• The environment changes to better suit the organisms' needs.

• Individual organisms learn to develop new traits during their life.

• All harmful mutations are immediately removed from the population.

Multiple Choice

Why did traits like antibiotic resistance and long legs become more widespread in their respective populations?

• The traits were developed because the organisms needed to survive.

• The traits provided a survival and reproductive advantage in a specific environment.

• The traits were passed on to other organisms through direct contact.

• The traits made the organisms stronger but reduced their ability to reproduce.

Multiple Choice

What must have been true for the populations of Salmonella, larkeys, and butterflies before the environmental challenges occurred?

• The advantageous traits arose from existing genetic variations or mutations within the populations.

• All individuals in the population simultaneously developed the new traits.

• The challenges in the environment directly caused the new traits to appear.

• The organisms were able to choose which traits to pass on to their offspring.

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Modeling Natural Selection

• Scientists use graphs and statistics to track how traits change over generations.

• A line graph could show dark moth populations increasing in a polluted forest.

• These models show the cause-and-effect relationship between environment and natural selection.

• They describe trends, not certainties, because of the role of probability.

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Multiple Choice

What is the primary purpose of using tools like graphs and statistics to model natural selection?

• To track and show how the traits of a population change over time.

• To prove that a specific animal will survive.

• To change the environment to help animals.

• To create new traits within a population.

Multiple Choice

A line graph showing an increase in dark moths in a polluted forest is used to illustrate what kind of relationship?

• The relationship between an environmental change and its effect on a population's traits.

• The exact number of dark moths that will exist in the future.

• The reason why individual moths change color during their lifetime.

• The history of all forests, regardless of pollution levels.

Multiple Choice

If a scientific model predicts that a species' average beak size will increase over many generations, what does this prediction represent?

• A likely trend that may occur due to the role of probability.

• A definite outcome that is guaranteed to happen.

• A result that is true for every individual in the population.

• An outcome that is completely random and unpredictable.

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Common Misconceptions

Misconception	Correction
Organisms try to adapt.	Adaptation is not a choice. Random mutations can be beneficial for survival.
Natural selection is always slow.	It can be rapid, as seen in the blue moon butterfly.
Individual organisms evolve.	Populations evolve over generations, not individuals within their lifetime.
Adaptation is always successful.	Rapid environmental changes can cause extinction if a population cannot adapt.

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Summary

• Natural selection requires variation, heritability, and different reproductive success.

• Random mutations are the source of new adaptations.

• A trait’s helpfulness depends on its specific environment.

• Mathematical models show how the distribution of traits changes over time.

• Environmental changes can cause shifts in the frequency of inherited traits.

• Extreme environmental shifts can lead to extinction if adaptation doesn't occur.

Poll

On a scale of 1-4, how confident are you about explaining natural selection using an example?

• 1

• 2

• 3

• 4