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?