Natural selection

Descent With Modification: A Darwinian View of Life

History of Evolutionary Thought

  • Early belief: The Old Testament asserts that species were individually designed by God, implying they are perfect.

  • Concept of design: The Creator designed each species for a specific purpose, and organismal adaptations serve as evidence of this design.

  • Foundational figure: Carolus Linnaeus, known for:

    • Modern taxonomy: Introduced binomial nomenclature.

    • Nested hierarchy in classification.

Binomial Nomenclature and Hierarchical Classification

  • Example of classification:

    • Species: Cardinalis cardinalis

    • Genus: Cardinalis

    • Family: Fringillidae

    • Order: Passeriformes

    • Class: Aves

    • Phylum: Chordata

    • Kingdom: Animalia

    • Domain: Eukarya

Timeline of Evolutionary Thought

  • 1795: James Hutton proposes gradualism, suggesting that Earth's surface changes occur from slow, continuous actions.

  • 1798: Thomas Malthus publishes "Essay on the Principle of Population" discussing population growth versus resource availability.

  • 1809: Charles Darwin is born.

  • 1809: Lamarck publishes his hypothesis of evolution, proposing a mechanism for species change.

  • 1830: Charles Lyell publishes "Principles of Geology," advocating uniformitarianism.

  • 1831-1836: Darwin travels around the world on the HMS Beagle; collects specimens and observes adaptations.

  • 1844: Darwin writes his essay on descent with modification.

  • 1858: Alfred Russel Wallace sends Darwin his ideas on natural selection.

  • 1859: Darwin publishes "On the Origin of Species."

Key Principles of Paleontology

  • Paleontology: The study of fossils, which are remains or traces of organisms from the past.

  • Georges Cuvier's concept: Catastrophism, where each stratum boundary signifies a catastrophe.

  • James Hutton's principle of gradualism: Proposes that Earth's changes are the result of slow processes, illustrated with examples like canyons formed by rivers.

Uniformitarianism

  • Charles Lyell's principle: The mechanisms of geological change are constant over time, emphasizing processes like:

    • Weathering

    • Uplift and exposure

    • Transportation and deposition

    • Lithification

Malthus' Population Theory

  • Observations: Populations can grow exponentially, while resources only increase linearly.

  • Resulting struggle for existence due to limited resources and high mortality rates.

Lamarck's Theory of Evolution

  • Main ideas:

    • Organisms could adapt through acquired traits within their lifetime.

    • Mechanisms included:

    • Use and disuse: Organs not used would diminish, while those in constant use would increase in size (e.g., tapeworms, bat ears).

    • Inheritance of characteristics: Adapted traits could be passed to offspring.

Charles Darwin's Contributions

  • Life span: 1809-1882, showing a lifelong interest in nature rather than medicine.

  • Voyage on the HMS Beagle:

    • Role: Invited as a gentleman companion and the ship’s naturalist for a journey charting South America.

    • Events: Collected specimens and observed adaptations in diverse environments.

    • Notable stop: Galapagos Islands, 500 miles off the coast of Ecuador.

    • Resulted in significant findings regarding biodiversity and species adaptations.

Darwin's Observations on the Galapagos Finches

  • Discovery: Collected various birds, discovering all 14 species were finches—now known as "Darwin's finches."

  • Main observation: No finch species existed on the mainland to compare with the Galapagos.

Adaptation and Speciation

  • Focus: Adaptation to environments leads to the formation of new species.

  • Observations on finches:

    • Variations in beak sizes corresponded to dietary needs (e.g., cactus-eater, insect-eater, seed-eater).

    • Changes occurred over generations leading to anatomical and behavioral alterations, resulting in speciation.

Reluctance and Publication of Darwin's Ideas

  • Return to England: After his voyage in 1836, he drafted a paper discussing species formation but hesitated to publish.

  • 1858: Alfred Russel Wallace's letter prompted Darwin to publish his own findings to avoid losing credit.

  • Landmark publication: On November 24, 1859, Darwin's "On the Origin of Species" was released.

Core Concepts from The Origin of Species

  • Two main ideas:

    • Descent with modification: Explains life's unity and diversity, emphasizing common ancestry.

    • Natural selection: Identifies adaptive evolution as a key mechanism.

Descent with Modification

  • Note: Darwin never used the term 'evolution' in the first edition; instead, he summarized it under descent with modification.

  • Analogy: The history of life resembles a tree with branches depicting diverse forms of life.

Darwin's Observations Supporting Natural Selection

  • Observation #1: Diversity within populations; individuals often vary significantly in traits.

  • Observation #2: Traits inherited from parents affect offspring.

  • Observation #3: Species produce more offspring than can survive due to limited resources.

  • Observation #4: Resource limits lead to high mortality among offspring.

Inferences from Observations

  • Inference #1: Individuals with advantageous inherited traits are more likely to survive and reproduce, leaving more offspring.

  • Inference #2: Differential survival and reproduction amplify favorable traits in populations over generations.

Natural Selection Summary

  • Definition: Individuals with certain heritable characteristics survive and reproduce at a higher rate than others.

  • Consequence: Natural selection drives adaptation to environments over time, contributing to the emergence of new species.

  • Key point: Natural selection can only act on heritable traits that vary within a population, with adaptations varying based on environmental contexts.