(148) History of Evolutionary Thought

Introduction to Evolutionary Thought

• Overview of evolutionary theory development leading to Darwin's contributions.

• Learning targets outlined to guide discussions on historical beliefs, Darwin's voyage, and modern synthesis concepts.

Early Scientific Beliefs About Evolution

Aristotle's Contribution

• Recognized complexity in organisms and the idea of identical individuals within a species.

• Influenced the scientific thought of future generations.

Count Buffon's Radical Ideas

• Proposed species arose from common ancestors and underwent change.

• Introduced a scientific perspective on evolution but lacked a mechanism for change.

Carolus Linnaeus and Taxonomy

• Developed binomial nomenclature system (two-part name for species).

  • Example: Genus name (capitalized) + species name (lowercase), both italicized or underlined.

• Believed in the fixity of species and Scala Naturae (literally a "ladder" of life).

Key Figures Influencing Evolutionary Thought

Erasmus Darwin

• Proposed ideas about species changes, animal breeding, and vestigial structures.

• Suggests possibility of evolution but no mechanism for change.

Baron Georges Cuvier

• Identified fossils, known for catastrophism theory (major geological changes caused by catastrophic events).

James Hutton and Charles Lyell

• Challenged catastrophism with uniformitarianism (slow and continuous geological processes).

Lamarck's Hypothesis of Evolution

• Introduced the law of use and disuse (traits developed through use are inheritable).

• Example: Giraffes' long necks evolved by stretching to reach food.

Darwin's Influences Before the Voyage

Malthus's Principle of Population

• Stated that population growth is limited by resources, disease, and war.

• Influenced Darwin's notions of competition and natural selection.

The Voyage of Charles Darwin

HMS Beagle Expedition

• Darwin joined as a naturalist, collecting specimens and making observations.

• Encountered diverse species and geological observations that influenced his ideas about evolution.

Key Observations During the Voyage

• Discovered fossils of glyptodonts related to armadillos, promoting thoughts on relatedness and change in species.

• Observed unique adaptations in species such as Patagonian hares and tortoises of Galapagos Islands.

The Concept of Natural Selection

Darwin's Main Argument

1. Variation in species is heritable (e.g., Asian ladybird beetles).

2. Limited resources lead to struggle for existence (e.g., elephant population example).

3. More offspring are born than can survive.

Giraffes as a Visual Aid

• Adaptation to competition for food resources leads to natural selection.

• Adaptive traits increase survival and reproductive success over generations.

Summary of Darwin's Observations

• In 1930s, connection between natural selection and genetics recognized.

• Modern evolutionary synthesis combines natural selection with Mendelian genetics to explain evolution.

  • Mutations create heritable variation acting as raw material for natural selection.

  • Evolution occurs in populations, not individuals, through gradual changes leading to speciation.

Conclusion

• Recap of today's lesson on evolutionary theory development and natural selection.

• Encouragement for questions to be submitted on exit tickets for further clarification.