Lesson 3: Natural Selection & Evolution
Evolution is the change in inherited traits in a population over successive generations. Natural selection is the primary mechanism: individuals with traits better suited to their environment are more likely to survive and reproduce, passing those traits on.
Key Concepts
Variation
Individuals in a population differ in their traits. Some variation is heritable (passed from parents to offspring through genes).
Selection Pressure
Environmental factors — predators, disease, food availability, climate — act as selection pressures. They determine which traits are advantageous in a given environment.
Survival of the Fittest
This phrase means 'survival of the best-fit to the environment,' not the strongest. A bacterium resistant to antibiotics is 'fitter' in a hospital environment.
Adaptation
Over many generations, favorable traits become more common. The population becomes better adapted to its environment. This is evolution.
Evidence for Evolution
Fossil records, comparative anatomy (homologous structures), molecular biology (shared DNA sequences), and direct observation (antibiotic resistance, dog breeding) all support evolution.
🔬 Virtual Lab: Natural Selection Simulator
A population of colored moths lives on tree bark. Click 'Hunt' to act as a predator — you'll catch the moths that stand out most. Watch which color survives.
✅ Check Your Understanding
1. What does 'natural selection' act on?
2. Over many generations, natural selection tends to make a population:
3. Which is direct evidence of evolution happening in real time?