Biology · Grade 11 · Evolutionary Processes · Term 2

History of Evolutionary Thought

Students will trace the development of evolutionary theory from early ideas to Darwin's contributions and modern synthesis.

• Ontario Curriculum Expectations
• HS-LS4-1

About This Topic

Mechanisms of selection are the driving forces of evolutionary change. In this topic, students analyze how natural, sexual, and artificial selection alter the genetic makeup of populations over time. They explore how environmental pressures, such as climate change in the Canadian North or urbanization in the GTA, act as selective filters, determining which traits are passed on to the next generation.

The curriculum emphasizes that selection acts on individuals, but evolution occurs in populations. Students also look at how human-driven artificial selection has shaped our food and pets, and how sexual selection can lead to traits that seem counterintuitive for survival. This topic comes alive when students can physically model the patterns of selection using simulated environments and varying selective pressures.

Key Questions

1. Compare early theories of evolution with Darwin's theory of natural selection.
2. Analyze the key observations and inferences that led Darwin to his theory.
3. Explain how the modern synthesis integrates genetics with natural selection.

Learning Objectives

• Compare early theories of evolution, such as Lamarckian inheritance, with Darwin's theory of natural selection, identifying key differences in their proposed mechanisms.
• Analyze Darwin's observations of finches' beak variations and fossil records as evidence supporting his inferences about adaptation and descent with modification.
• Explain how the modern synthesis integrates Mendelian genetics with Darwinian natural selection to account for the mechanisms of evolutionary change.
• Evaluate the significance of key scientific contributions, including those of Darwin and Wallace, in shaping the trajectory of evolutionary thought.

Before You Start

Introduction to Genetics

Why: Students need a basic understanding of heredity and how traits are passed from parents to offspring to grasp how genetic variation fuels evolution.

Variation within Populations

Why: Understanding that individuals within a population exhibit differences is fundamental to comprehending how selection can act on these variations.

Key Vocabulary

Natural Selection	The process whereby organisms better adapted to their environment tend to survive and produce more offspring. It is a key mechanism of evolution.
Descent with Modification	The idea that species change over time and that new species arise from common ancestors. This is a core concept in Darwin's theory.
Artificial Selection	The breeding of plants and animals by humans for specific desirable traits, demonstrating that selection can cause significant change over generations.
Modern Synthesis	The early 20th-century fusion of Mendelian genetics with Darwinian evolution, explaining how genetic variation arises and is acted upon by natural selection.
Adaptation	A trait that increases an organism's fitness, or its ability to survive and reproduce in a particular environment. Adaptations arise through natural selection.

Watch Out for These Misconceptions

Common Misconception

Natural selection involves organisms 'trying' to adapt to their environment.

What to Teach Instead

Selection is a passive process; individuals with helpful traits simply survive and reproduce more. Using a simulation where students have no control over their 'traits' helps reinforce that evolution is not goal-oriented.

Common Misconception

The 'fittest' organisms are the strongest or fastest.

What to Teach Instead

Biological fitness is strictly about reproductive success. An organism that is slow but produces many offspring is more 'fit' than a fast one that produces none. Peer discussion of various animal life cycles can help clarify this definition.

Active Learning Ideas

Simulation Game: The Beaks of Finches

Students use different tools (tweezers, spoons, clips) to 'eat' various types of seeds. They track which 'beaks' are most successful in different environments and how the population's traits shift over several rounds.

50 min·Small Groups

Formal Debate: Artificial Selection in Agriculture

Groups debate the pros and cons of intensive artificial selection in modern farming. One side argues for increased yield and food security, while the other focuses on the loss of genetic diversity and vulnerability to disease.

45 min·Small Groups

Think-Pair-Share: Sexual Selection vs. Survival

Students look at images of extreme traits like a peacock's tail or a moose's antlers. They discuss with a partner how these traits might help an organism reproduce even if they make it easier for predators to find them.

15 min·Pairs

Real-World Connections

• Paleontologists, like those working at the Royal Tyrrell Museum in Alberta, reconstruct evolutionary histories by analyzing fossil evidence, providing tangible links to ancient life forms and their changes over geological time.
• Agricultural scientists utilize principles of artificial selection to develop new crop varieties with enhanced yields or disease resistance, directly impacting global food security and the products available in Canadian grocery stores.
• Medical researchers study antibiotic resistance in bacteria, a rapid example of natural selection in action, to develop new treatment strategies and understand how pathogens evolve to evade our defenses.

Assessment Ideas

Quick Check

Present students with a short passage describing a historical idea about evolution (e.g., Lamarck's giraffe). Ask them to write two sentences explaining why this idea differs from Darwin's concept of natural selection.

Discussion Prompt

Pose the question: 'Imagine you are a scientist in the 1860s. What evidence would most convince you that Darwin's theory of natural selection is valid?' Facilitate a class discussion, encouraging students to reference specific observations Darwin made.

Exit Ticket

Students receive a card with one term: 'Modern Synthesis'. Ask them to write one sentence defining it and one sentence explaining how it connects genetics to Darwin's ideas.

Frequently Asked Questions

What is the difference between natural and artificial selection?

In natural selection, environmental pressures determine which traits are advantageous. In artificial selection, humans choose which individuals breed based on desired characteristics, such as higher milk production in cows or specific colors in flowers.

How does antibiotic resistance show natural selection?

When bacteria are exposed to antibiotics, most die. However, if a few have a mutation that makes them resistant, they survive and multiply. Over time, the entire population becomes resistant because the 'selective pressure' (the antibiotic) killed off the non-resistant individuals.

Why is genetic variation necessary for selection to occur?

Without variation, every individual would respond to an environmental change in the exact same way. If a new disease or climate shift occurs and no one has a trait to survive it, the entire population could go extinct. Variation provides the 'raw material' for evolution.

How can active learning help students understand selection?

Active learning, particularly through simulations, allows students to see 'evolution in action' within a single class period. By physically acting as the selective pressure or the organism, they experience the statistical nature of evolution, making the shift from individual survival to population change much clearer.

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