Science · 8th Grade

Active learning ideas

The Mechanism of Natural Selection

Dive into the engine of evolution by exploring natural selection, the process that explains the incredible diversity of life on Earth.

• Common Core State Standards
• NGSS: LS4.B - Natural Selection

• 30–50 min
• Pairs → Whole Class
• 3 activities

Activity 01

• Simulation Game
• 45 min · Small Groups

Peppered Moth Simulation

Students act as 'bird predators' picking up light and dark paper moth cutouts from different colored backgrounds (representing pre- and post-industrial tree bark). They count the surviving moths of each color to see how the population's color frequency changes based on the environment.

Explain the key principles of natural selection: variation, inheritance, and differential survival and reproduction.

Facilitation Tip

Have groups graph their data and the class data to visualize the population shift more clearly.

What to look for

Use an exit ticket where students must explain the peppered moth scenario using the key terms: variation, inheritance, and selection.

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

Activity 02

• Simulation Game
• 50 min · Pairs

The 'Beak' of the Finch Lab

Students use different tools (tweezers, clothespins, spoons) to represent different bird beaks. They compete to 'eat' various food items (seeds, marbles, rubber bands) in timed trials to see which 'beak' is best suited for each food source, modeling adaptation and niche partitioning.

Analyze a scenario, like the peppered moths of England, to describe how environmental changes drive natural selection.

Facilitation Tip

Encourage students to discuss why a 'beak' that is successful with one food source might fail with another.

What to look for

Provide students with a novel scenario and data set (e.g., changes in fish size due to a new predator). Ask them to write a Claim, Evidence, Reasoning (CER) response explaining how natural selection caused the observed change.

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

Activity 03

• Simulation Game
• 30 min · Small Groups

Modeling Genetic Variation

Students use a population of diverse objects, like a bag of mixed beans, to represent a species. They apply a 'selective pressure', like removing all beans below a certain size, and observe how the characteristics of the next 'generation' (the remaining beans) have shifted.

Identify the role of genetic variation as the raw material for natural selection.

Facilitation Tip

Ask students to predict what would happen if the selective pressure changed, for example, favoring the smallest beans instead.

What to look for

Give students a checklist of the learning objectives and have them rate their confidence level (e.g., 'I can teach this,' 'I understand this,' 'I need help') for each one.

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

A few notes on teaching this unit

Start with a concrete phenomenon like the peppered moth to anchor the abstract concepts. Use simulations and modeling activities to allow students to 'experience' the process. Consistently reinforce the vocabulary: variation is the raw material, inheritance passes traits on, and the environment selects for the most suitable traits.

Students will be able to analyze scenarios and explain how variation, inheritance, and environmental pressures drive changes in populations over time.

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Watch Out for These Misconceptions

• Organisms can 'try' or 'choose' to adapt to their environment out of need.

  Adaptation is not a conscious choice. The variation of traits already exists in the population due to random genetic mutations. The environment then 'selects' for the individuals with traits that are already well-suited for survival and reproduction.

• 'Survival of the fittest' means only the strongest, fastest, or biggest organisms survive.

  In biology, 'fitness' refers to an organism's ability to survive and reproduce in its specific environment. The 'fittest' individual might be the best camouflaged, the most efficient at finding food, or the one that is best at conserving energy, not necessarily the strongest.

• Natural selection is a linear process that creates 'perfect' organisms.

  Evolution is not goal-oriented and does not lead to perfection. It is a branching process that results in adaptations that are beneficial in a particular environment at a particular time. A trait that is advantageous now may become disadvantageous if the environment changes.

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Methods used in this brief

• Simulation Game