Chapter 22 Darwinian Evolution

Chapter 22: Descent with Modification: A Darwinian View of Life

Timeline of Evolutionary History

  • 10,000 years ago: Mammut (mastodon)

  • Millions of years ago:

    • 5.5 million years: Deinotherium

    • 24 million years: Barytherium

    • 34 million years: Moeritherium

Key Species Represented

  • Modern Species:

    • Loxodonta (African elephant)

    • Elephas maximus (Asian elephant)

    • Mammuthus (mammoth)

    • Platybelodon

    • Human

    • Cat

    • Whale

    • Bat

Evolutionary Mechanisms

  1. What Is the Relationship between Fact and Theory in Evolution?

  2. What Are the Mechanisms of Evolutionary Change?

  3. How Do Biologists Measure Evolutionary Change?

  4. How Is Genetic Variation Maintained within Populations?

  5. What Are the Constraints on Evolution?

Theoretical Foundations of Evolution

  • Definition of a Scientific Theory: A theory accounts for numerous observations and findings, attempting to explain and integrate a wide range of phenomena.

  • Historical context: The belief that life forms originated separately and were static was prevalent 200 years ago.

Historical Perspectives on Species

  • Aristotle: Viewed species as fixed and unchanging.

  • Old Testament: Suggested species were individually designed by God.

  • Carolus Linnaeus: Founder of taxonomy, classified species for the glory of God, seeing adaptations as evidence of purposeful design.

Fossil Evidence

  • What Do Fossils Reveal?: Fossils are remains or traces of organisms from the past, typically found in sedimentary rock which is composed of layers or strata.

  • Fossil Timeline:

    • Notable eras:

    • Age of Insects and Reptiles: 570 million years ago to 65 million years ago

    • History of mammals begins soon thereafter.

    • Recorded human history begins about 1/4 second before midnight on a 24-hour timeline representing Earth's history.

Mechanisms of Evolution

  • Homologous Structures: Anatomical resemblances indicating common ancestry (e.g., forelimbs of human, cat, whale, bat).

Lamarck’s Evolutionary Hypothesis (1744-1829)

  • Proposed inheritance of acquired characteristics, exemplified by the giraffe's neck and blacksmith’s arm.

Darwin and Wallace’s Theory of Evolution (1859)

Undeniable Facts and Conclusions:

  1. Fast Reproduction Potential: Populations could reproduce rapidly.

  2. Population Size Stability: Population sizes remain constant over time.

  3. Variation within Populations: Individuals within a population exhibit variation.

  4. Heritability: Many traits are heritable.

  • Inferences:

    • Natural Selection: The fittest leave the most offspring.

    • Evolution: Gene frequencies within populations change over time due to natural selection.

Core Themes of Evolution

  • Evolution serves as the foundational theme in biology, encapsulated in Darwin's synthesis of natural selection, heritable variations, and overproduction of offspring leading to adaptation.

Mechanisms of Evolutionary Change

  • Microevolution: Refers to changes in genetic makeup within populations from generation to generation.

  • Natural Selection: Acts on individuals but populations evolve.

Adaptation and Evolution

  • Natural selection leads to adaptation of organisms to their environment, showcased by different traits expressed in various settings (e.g., aquatic vs. terrestrial).

Evidence for Evolution

  1. Fossil Records: Show clear succession and transitional forms supporting major evolutionary branches.

  2. Homologous Structures: Indicate common ancestry.

  3. Molecular Data: Homologous genetic sequences across species suggest relatedness.

  4. Biogeography: Distribution patterns that align with environmental adaptations.

  5. Comparative Embryology: Reveals homologies not apparent in adult forms.

  6. Vestigial Structures: The remnants of structures that served crucial functions in ancestral species (e.g., whale pelvis).

Drug Resistance and Evolution

  • Evidence of Natural Selection: Instances of insecticide resistance in populations and drug-resistant HIV; both examples illustrate natural selection acting on genetic variations.

Darwin’s Contributions

  • Two central ideas:

    1. Diversity and unity of life is explained by evolution.

    2. Natural selection is the key mechanism for adaptive evolution.

Initial Resistance to Evolutionary Ideas

  • The publication of "On the Origin of Species" in 1859 challenged long-held beliefs of a static Earth with unchanged species, creating a paradigm shift in biological sciences.

Conclusion

  • Darwin's theory of evolution by natural selection links diverse biological studies and opens avenues for ongoing research.