Darwin and Evolution

Theory of Evolution by Natural Selection: Proposed by Charles Darwin and Alfred Russel Wallace, this theory explains how species evolve over time through natural selection. Biological diversity, which refers to the vast variety of life forms in Earth's ecosystems, emerges from this evolutionary process.

Historical and Scientific Context

• Pre-19th Century Beliefs: Scientific thought was dominated by the notion of fixed species, which posited that all life forms had remained unchanged since their inception, without acknowledging variation within species.
• Darwin and Wallace's Contributions: They presented compelling evidence against the fixed species concept, demonstrating that species evolve over time. Important works include Darwin's On the Origin of Species and Wallace's studies in the Malay Archipelago. Their research challenged existing religious doctrines.
• Resistance: Early opposition arose from religious groups and scientific traditionalists who felt that evolution conflicted with creationist views.

Core Principles of Natural Selection

• Variation: Differences among individuals within a species, such as the colour variations in peppered moths, can influence survival.
• Competition: Organisms vie for finite resources such as food and habitat.
• Survival of the Fittest: Characteristics that offer survival benefits, like long necks in giraffes for accessing tall trees, become more common in populations.
• Inheritance: Traits that confer advantages are passed down through generations.

Timeline of Life Diversification

• Extends from the origin of life through key events like the Cambrian explosion and the development of multicellularity.
• Adaptive radiations, exemplified by Darwin's finches, occur as species fill new niches following extinction events.
• Extinctions, such as the disappearance of dinosaurs, paved the way for mammalian diversification.

Microevolution vs. Macroevolution

• Microevolution: Small genetic changes within a species, such as antibiotic resistance in bacteria, can have significant impacts, particularly on medical treatment efficacy.
• Macroevolution: Involves broader, long-term evolutionary changes across different species.

Case Studies

Horse Evolution

• An increase in size contributed to better survival prospects.
• Limb adaptations and dental changes enabled improved mobility and dietary diversity. Fossil records illustrate these evolutionary adaptations.

Platypus Evolution

• Adaptations such as venom and electroreception developed in response to environmental pressures.

Genetic Influences and Geographic Isolation

• Mutations: Random genetic changes that enhance adaptation.
• Selection Pressures: Environmental factors that influence survival.
• Geographic Isolation: The emergence of new species occurs due to physical barriers restricting gene flow.

Convergent vs. Divergent Evolution

Convergent Evolution: Unrelated species independently evolve similar traits in response to similar environmental pressures.

• Examples:
  • Succulent features in cacti and euphorbias in arid environments.
  • Wings in bats and birds evolved for flight.

Divergent Evolution results in increased biodiversity.

• Examples:
  • Variations in finch beaks on the Galápagos Islands.

Punctuated Equilibrium vs. Gradualism

• Punctuated Equilibrium: Rapid evolutionary changes occur in sudden bursts.
• Gradualism: Evolution happens in a slow and continuous manner.

Gould and Eldredge: Their idea of Punctuated Equilibrium challenged Darwin's concept of gradualism.

Exam Tip

Notable Contributions

Societal and Scientific Impact

• The theory of evolution informs practices in biodiversity conservation and medicine.
• Economic and cultural acceptance: Evolutionary theory has significantly influenced education and policy, highlighting its extensive impact.