Giant Tortoises and Darwin's Finches

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Darwin’s discoveries in the Galápagos continued beyond the iguanas. The islands were named after giant tortoises—huge reptiles so big that two people could ride on them!

As Darwin observed them, he noticed they looked different depending on where they lived.

For example, on islands where food was close to the ground, the tortoises had short necks and rounded shells. However, on islands with tall plants, they developed long necks and curved shells that helped them stretch up to reach food.

In addition to the tortoises, Darwin also studied finches—small birds that lived on the islands. At first, he didn’t realize they were all finches because they looked different on each island. Later, he found that the key difference was their beaks.

For instance, finches that ate large seeds had larger beaks, while those that ate small seeds had smaller beaks. Over time, their beaks adapted to match their food sources, helping them survive.

Based on these observations, Darwin developed the theory of natural selection, which states animals change over generations, passing on traits that help them survive.

Overview

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Giant Tortoises and Darwin's Finches

Giant tortoises and Darwin’s finches are two famous examples that helped shape the theory of evolution. Charles Darwin observed these animals on the Galápagos Islands during his voyage on the HMS Beagle. He noticed that tortoises from different islands had different shell shapes, adapted to the food and environment of each island. Finches had different beak shapes based on the types of food they ate. These observations showed how species adapt over time to their surroundings, providing key evidence for natural selection.

Science and Engineering Practices (SEP): Analyzing and Interpreting Data

Scientists analyze and interpret data to determine similarities and differences in how organisms adapt to different environments. By comparing shell shapes of tortoises and beak sizes of finches, scientists use data to reveal how traits are passed on and modified over time. This analysis helps distinguish between correlation and causation and supports conclusions about natural selection.

Activity Ideas:

Beak Shape Simulation – Use tools like tweezers, spoons, or chopsticks to mimic different beak shapes and test how well they gather various types of food.
Shell Shape Analysis – Compare images or models of tortoise shells and identify how the structure relates to function and habitat.
Data Interpretation Practice – Examine real or simulated graphs showing changes in finch beak size over time and relate them to environmental conditions.

Crosscutting Concept (CCC): Patterns

Graphs, charts, and images reveal patterns in animal traits that provide insight into evolutionary change.

Pattern: Different beak shapes among finches.
Effect: Each shape is suited to a specific type of food, demonstrating adaptation.
Pattern: Variation in tortoise shell height.
Effect: Allows access to different vegetation and supports survival on other islands.
Pattern: Trait changes linked to environmental changes.
Effect: Show how natural selection works in response to available resources.

Connections to Nature of Science

Scientific knowledge is based on empirical evidence. Observations and measurements of giant tortoises and finches provide logical and conceptual connections between evidence and explanations. Science assumes order and consistency in natural systems, and the patterns observed in these animals reflect predictable processes that can be measured and studied over time.

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