A4.1 Evolution and Speciation

4.1 Evolution and Speciation

A4.1.1: Definition of Evolution

  • Theories of Evolution

    • Change in heritable characteristics of a population over time.

    • Distinguishes Darwinian evolution from Lamarckism: only genetic changes are evolution.

  • Nature of Science

    • Evolution by natural selection predicts and explains a wide range of observations, unlikely to be falsified.

    • Praised as a strong, pragmatic theory, even if it cannot be formally proven.

A4.1.2: Evidence for Evolution

  • Types of evidence supporting evolution:

    • DNA, RNA and protein sequences.

    • Homologous Structures.

    • Selective Breeding.

A4.1.3: Selective Breeding

  • Definition

    • Process where humans breed plants/animals for specific traits.

  • Shows rapid evolutionary changes.

  • Examples include domesticated animals like dogs (from wolves) and crop plants like Brassica oleracea.

A4.1.4: Homologous Structures

  • Definition

    • Similar structures in different species evolved from a common ancestor.

  • Example: Pentadactyl limb found in humans, birds, dogs, and whales has structural similarities adapted for different functions (grasping, running, flying, swimming).

A4.1.5: Analogous Structures

  • Definition

    • Structures with similar functions but differing origins; do not arise from a common ancestor.

  • Example: Wings of bats, birds, and insects evolve through convergent evolution.

A4.1.6: Speciation

  • Definition

    • Formation of new species as a result of evolutionary processes.

  • Occurs when populations are reproductively isolated.

  • Gradual change within a species does not constitute speciation.

A4.1.7: Reproductive Isolation

  • Types of Isolation

    • Geographical: Prevents interbreeding across physical barriers (e.g., rivers, mountains).

    • Behavioral: Different mating behaviors lead to reproductive barriers (e.g., different songs in meadowlarks).

    • Temporal: Species breeding at different times (e.g., cicadas with different life cycles).

Evolution of Chimpanzees and Bonobos

  • Common ancestor of chimpanzees and bonobos was geographically isolated by the Congo River.

  • Led to different traits being selected on either side, resulting in speciation.

4.1.8: Sympatric vs Allopatric Speciation

  • Allopatric Speciation: Occurs due to geographical isolation.

  • Sympatric Speciation: Occurs without geographical barriers; reproductive isolation can arise via behavioral or temporal means.

Adaptive Radiation

  • Definition

    • Rapid evolution of one species into multiple new species as they adapt to various ecological niches.

    • Example: Darwin's finches evolved from a single ancestor into multiple species on the Galapagos Islands.

4.1.9: Barriers to Hybridization

  • Types of Barriers

    • Prezygotic: Prevent fertilization (e.g., behavioral isolation, temporal isolation).

    • Postzygotic: Result in hybrid offspring that are inviable or sterile (e.g., mules).

Polyploidy

  • Definition

    • Condition of having more than two sets of chromosomes, commonly seen in plants.

    • Can cause immediate speciation.

Key Terms

  • Evolution, Speciation, Homologous Structures, Analogous Structures, Selective Breeding, Common Ancestor, Pentadactyl Limb, Reproductive Isolation, Geographical Isolation, Convergent Evolution, Adaptive Radiation, Biodiversity.

Review Questions

  • How does the theory of evolution by natural selection explain the unity and diversity of life on Earth?

  • What counts as strong evidence in biology?

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