Quick Summary
Evolution explains biological change across generations. Variation appears in populations, and natural selection acts on that variation. Over time, allele frequencies may change and new forms can arise.
Evidence for Evolution
- Fossils
- Comparative anatomy
- Homologous organs
- Analogous organs
- Embryological evidence
- Molecular evidence
Darwin's Main Ideas
1. Overproduction 2. Struggle for existence 3. Variation 4. Survival of the fittest 5. Natural selection
Homologous vs Analogous Organs
| Homologous Organs | Analogous Organs |
|---|---|
| Same basic origin | Different origin |
| May perform different functions | Perform similar functions |
| Indicate divergent evolution | Indicate convergent evolution |
Hardy-Weinberg Principle
Allele frequencies remain constant in an ideal population when evolutionary forces are absent.
Factors that disturb equilibrium:
- mutation
- gene flow
- genetic drift
- natural selection
- non-random mating
Adaptive Radiation
Diversification of related organisms from a common ancestor into different ecological niches.
Important Questions
One Mark
1. Define evolution. 2. Name one evidence for evolution. 3. Which organs indicate divergent evolution?
Short Answer
1. Distinguish between homologous and analogous organs. 2. State Darwin's major ideas. 3. Name factors affecting Hardy-Weinberg equilibrium.
Long Answer
1. Explain the evidences for evolution. 2. Explain natural selection. 3. Explain Hardy-Weinberg principle and factors disturbing equilibrium.
Common Mistakes
- Writing evolution as change in one individual during life.
- Reversing homologous and analogous examples.
- Treating fitness as physical strength only.
- Listing Hardy-Weinberg factors without naming the principle.
Revision Checklist
- [ ] Evidence for evolution
- [ ] Darwin's five ideas
- [ ] Homologous vs analogous organs
- [ ] Hardy-Weinberg principle
- [ ] Adaptive radiation