Evolution and Natural Selection

Overview

This 70-minute lesson introduces 8th-grade students to the foundational concepts of evolution and natural selection. Students will engage in inquiry-based learning aligned with the Next Generation Science Standards (NGSS), focusing on understanding variation within populations, environmental pressures, and survival of traits beneficial for reproductive success.

NGSS Alignment

Performance Expectations:

MS-LS4-2: Construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals’ probability of surviving and reproducing in a specific environment.
MS-LS4-4: Construct an argument supported by empirical evidence that changes in environmental conditions may result in increases or decreases of organisms with specific traits in a population over time.

Disciplinary Core Ideas (DCIs):

LS4.B: Natural Selection – Natural selection leads to the predominance of certain traits in a population, and the suppression of others. (MS-LS4-2)
LS4.C: Adaptation – Different kinds of organisms adapt to their environments in different ways.

Science & Engineering Practices (SEPs):

Engaging in argument from evidence
Constructing explanations and designing solutions
Analyzing and interpreting data

Crosscutting Concepts (CCCs):

Cause and Effect: Mechanism and explanation
Patterns

Learning Objectives

By the end of this lesson, students will be able to:

Explain how variation exists within a population and why it matters for survival.
Describe the basic mechanisms of natural selection: variation, competition, survival of the fittest.
Analyze how environmental factors can influence which traits are advantageous and how those traits may change in a population over time.
Use evidence to construct a simple explanation of natural selection.

Materials Needed

Whiteboard and markers
Colored index cards or paper slips with different “traits” written or illustrated (e.g., fur color, beak size, speed)
Large poster or projected environmental scenario images (e.g., desert, forest, arctic)
“Organism” tokens or counters (can be beans, buttons, or printed images)
Student notebooks or science journals
Projector or chart paper for group summaries

Lesson Breakdown

1. Introduction & Anticipatory Set (10 minutes)

Engage students: Begin by posing the question, “Why do you think some animals look very different from others but are still part of the same species?”
Facilitate a brief think-pair-share where students discuss initial thoughts about animal diversity.
Show images of diverse species (e.g., finches with different beak shapes, peppered moths) and explain that today’s lesson will explore why these differences exist and how they help organisms survive.
Connect the discussion to the idea of evolution and natural selection.

2. Direct Instruction & Discussion (15 minutes)

Define key terms: evolution, natural selection, variation, adaptation, survival of the fittest.
Use the whiteboard or a visual concept map to diagram the mechanism of natural selection:
- Variation in traits → competition for resources → differential survival → reproduction → change in population traits over generations.
Present an environmental scenario (e.g., birds living in a forest with large seeds) and ask: “Which traits would help these birds survive?”
Encourage students to explain why some traits could give an advantage.

3. Hands-On Activity: Natural Selection Simulation (30 minutes)

Setup: Divide class into groups of 5. Each group receives a mix of “organism” tokens representing individuals with different traits (use colors or labels to differentiate).
Present an environmental condition (e.g., drought, increased predators, cold climate). The teacher will describe how this environment favors certain traits.
Groups simulate “survival” by selecting which “organisms” survive based on the environment. Students remove “organisms” tokens that do not have the favored traits. The survivors “reproduce” by doubling their tokens representing offspring inheriting the traits.
Repeat for 2-3 environmental changes to simulate several generations, changing which traits are favored.
After the simulation, groups create a mini report or diagram showing how the population traits changed over generations and why.

4. Group Discussion & Explanation Construction (10 minutes)

Each group presents their results and explains how the environmental changes affected which traits were advantageous and how the population evolved.
As a class, discuss patterns observed and link back to the concepts of natural selection and adaptation.
Prompt students to construct oral explanations supported by evidence from their simulations.

5. Exit Ticket / Quick Assessment (5 minutes)

Students write 3-4 sentences answering: “How does natural selection cause populations to change over time? Use evidence from today’s activity.”
Collect for formative assessment to gauge individual student understanding.

Differentiation Strategies

For students needing support: Provide scaffolded sentence starters for explanation construction; pair with peers during activities.
For advanced learners: Challenge them to predict what might happen if environment changes quickly or if new traits are introduced.

Reflection & Next Steps

For Lesson 2, students will explore evidence from fossils and DNA to deepen understanding of evolutionary change.
Teacher to review exit tickets for misconceptions, adjust future lessons to clarify complex ideas (e.g., difference between individual change vs. population change over time).

Teacher Tips to Impress

Encourage student voice by having them be “scientists” explaining their hypotheses and conclusions.
Use real-life examples (Galapagos finches, antibiotic resistance) to make abstract concepts tangible.
Consider recording or photographing group work for student portfolios or parent communication.
Be ready to highlight “wow moments” when students connect environmental change directly with trait survival, demonstrating understanding.

This plan integrates NGSS rigor with hands-on student engagement, ensuring students not only grasp evolution concepts but can think and communicate like scientists—a crucial step in cultivating scientific literacy.

Teaching Instructions