Lesson 2: Debating Stickleback Evolution

Key Idea

Why would losing armor be good? Traits often have trade-offs. Armor offers protection, but it is heavy and slow. Low armor offers less protection, but allows for speed.

In the lake environment, the main predator is the Dragonfly Larva, which grabs slow fish. Therefore, being fast (Low Armor) is an adaptive trait, while being armored (but slow) is non-adaptive.

Key Idea

We can now build a scientific argument for the Stickleback shift:

• Claim: The population evolved Low Armor because of dragonfly predation.
• Evidence: Data shows Low Armor fish are faster and survive dragonfly attacks better.
• Reasoning: Because fast fish survived and reproduced, they passed the "Low Armor" genes to the next generation, shifting the population.