Unit 13: Evolution and Natural Selection

1. Charles Darwin and the Theory of Evolution

• Voyage on the HMS Beagle:

  • Observed variations in species, particularly finches in the Galápagos Islands.

  • Developed the theory of natural selection to explain adaptation and speciation.

• Key Influences on Darwin:

  • Geologists Lyell & Hutton: Earth is old and changes gradually.

  • Thomas Malthus: Populations grow faster than resources, leading to competition.

2. Principles of Natural Selection

1. Variation: Differences exist within populations.

2. Overproduction: More offspring are produced than can survive.

3. Competition: Organisms compete for resources.

4. Survival of the Fittest: Individuals with beneficial traits are more likely to survive and reproduce.

5. Descent with Modification: Favorable traits become more common over generations.

3. Evidence Supporting Evolution

• Fossil Record: Shows gradual changes in organisms over time.

• Comparative Anatomy:

  • Homologous Structures: Same structure, different function (e.g., human arm, bat wing).

  • Analogous Structures: Different structure, same function (e.g., bird wings vs. insect wings).

  • Vestigial Structures: Reduced or non-functional remnants of ancestors (e.g., human tailbone).

• Embryology: Similar embryos suggest common ancestry.

• Biogeography: Species in similar environments evolve similarly (convergent evolution).

• Molecular Biology: Similar DNA and proteins indicate evolutionary relationships.

4. Mechanisms of Evolution

• Genetic Drift: Random changes in allele frequency, especially in small populations.

• Gene Flow: Movement of genes between populations through migration.

• Mutations: Source of new genetic variations.

• Natural Selection: Differential survival and reproduction of individuals with advantageous traits.

5. Adaptations and Survival of the Fittest

• Structural Adaptations: Physical traits (e.g., camouflage, mimicry).

• Behavioral Adaptations: Actions that improve survival (e.g., migration, hibernation).

• Physiological Adaptations: Internal body processes (e.g., venom production, antibiotic resistance).

6. Heritable Variation and Evolutionary Fitness

• Heritable Traits: Passed down through generations, contributing to evolutionary change.

• Fitness: The ability of an organism to survive and reproduce.

• Artificial Selection: Human-driven breeding for desired traits (e.g., dog breeds, crop modifications).

Connections to Other Units:

• Genetic mutations (Unit 12) create variations that drive evolution.

• Population genetics (Unit 12) and evolutionary forces (Unit 14) shape species over time.

• Environmental pressures (Unit 6) influence survival and adaptation.

Let me know when you’re ready for the next unit!