Biology · Ch 6 — Evolution
Summary
Summary
- Origin of life: Oparin-Haldane theory proposed life arose from non-living matter via chemical evolution. Miller-Urey experiment simulated early Earth conditions (CH₄, NH₃, H₂, water vapour, electric sparks) and produced amino acids, supporting abiogenesis.
- Evidence for evolution: Homologous organs (same basic structure, different functions — e.g., forelimbs of vertebrates) show common ancestry. Analogous organs (different origins, similar functions — e.g., wings of bird and insect) show convergent evolution. Fossils, embryology, and molecular homology (DNA/protein sequence similarity) provide additional evidence.
- Darwin's theory: Natural selection acts on heritable variation; individuals with advantageous traits survive and reproduce more, leading to adaptive evolution. Overproduction, limited resources, and struggle for existence drive this.
- Modern synthetic theory: Combines Darwinian selection with genetics — mutations, genetic recombination, gene flow, genetic drift, and natural selection together cause evolution. Hardy-Weinberg principle: allele frequencies remain constant in a large, random-mating population without evolutionary forces; p² + 2pq + q² = 1 for a two-allele locus.
- Mechanisms of evolution: Genetic drift (random change in allele frequency, especially in small populations — founder effect). Gene flow (migration) introduces or removes alleles. Natural selection can be directional, stabilising, or disruptive. …