Copy of Ch. 22 2024

Chapter 22 - Darwinian Evolution

Introduction to Evolutionary Theory

• Date of Significance: November 24, 1859, marked the publication of Charles Darwin's On the Origin of Species by Means of Natural Selection.

  • This work sold out rapidly, signifying a profound impact on science.

• Key Themes:

  • Focus on the diversity of life forms.

  • Evidence presented for the derivation of current species from ancestral species.

  • Introduction of natural selection as a pivotal mechanism for evolution.

Understanding Evolution

• Definition: Evolution is the change over time in the genetic makeup of populations.

• Natural Selection: Individuals with advantageous heritable traits reproduce more than others, resulting in differential reproductive success.

• Evolutionary Adaptations: Traits that enhance an organism's ability to survive and reproduce become more prevalent in the population.

Influences on Darwin’s Ideas

• Influential Figures:

  • Carolus Linnaeus: Developed taxonomy, placing emphasis on God's glory through classification of organisms.

  • Georges Cuvier: Opposed gradual change suggesting catastrophism, where strata changes were signs of past disasters.

  • James Hutton and Charles Lyell: Advocated for gradualism and the principle of uniformitarianism; changes in Earth’s geology are due to slow, continuous processes.

  • Jean-Baptiste Lamarck: Proposed incorrect mechanisms for evolution through use and disuse, suggesting that acquired traits could be inherited.

Lamarck’s Theories and Examples

• Lamarck vs. Darwin:

  • Lamarck: suggested use/disuse & gained traits lead to complexity.

  • Darwin: advocated for variation, inheritance, differential survival, and extinction.

• Examples:

  • Giraffes stretching their necks lead to longer necks over generations.

Geologic Perspectives

• Lyell’s Gradualism: Understanding geological features requires studying ongoing processes (e.g., river erosion creating the Grand Canyon).

• Effects of Extinction: Recognized by Lyell, reflecting on species that no longer exist (e.g., dinosaurs).

Linnaean Taxonomy

• Classification Hierarchy:

  • Species, Genus, Family, Order, Class, Phylum, Kingdom.

  • Example: Homo sapiens classified as:

    • Homo: Genus including intelligent humans.

    • Primates: Group with advanced vision.

Malthus's Population Theory

• Thomas Malthus (1798): Examined the relationship between population growth and food supply:

  • Populations grow geometrically (1, 2, 4, 8...) while food supply grows arithmetically (1, 2, 3, 4...).

  • Predicts Malthusian catastrophe where scarcity leads to conflict and famine.

Key Historical Figures in Evolution

• Integrated contributions from:

  • Linnaeus (taxonomy)

  • Hutton (gradualism)

  • Lamarck (evolution)

  • Malthus (population limits)

  • Cuvier (paleontology)

  • Lyell (geology)

  • Darwin (evolution and natural selection)

  • Mendel (genetics)

  • Wallace (evolution and natural selection)

Descent with Modification

• Observations:

  1. Exponential fertility of populations.

  2. Stable population sizes despite resource limits.

  3. Variation among individuals.

  4. Heritable traits are passed to offspring.

Darwin's Finches

• Diverse Adaptations:

  • Different species of finches show adaptations such as varied beak structures suited to their diets (insect eaters, fruit eaters, etc.).

Evidence of Evolution

• Biogeography: Geographic distribution of species indicates evolutionary relationships (e.g., Australia’s sugar gliders vs. North America’s flying squirrels).

• Fossil Record: Transitional links illuminate evolutionary history through succession of life forms over geological time.

• Comparative Anatomy:

  • Homologous Structures: Indicate a common ancestor (e.g., whale flippers and human arms).

  • Vestigial Organs: Structures that have lost their original function (e.g., human appendix).

Molecular Evidence

• Molecular Biology:

  • Similarities in DNA and proteins reveal evolutionary ties.

  • Molecular analysis provides a clearer understanding of species relationships compared to protein analysis.

Natural Selection and Adaptation

• Key Tenets of Natural Selection:

  1. Variation exists within populations.

  2. Traits are inheritable.

  3. Overproduction leads to competition.

  4. Individuals with advantageous traits are more likely to survive and reproduce.

• Adaptations: Traits that enhance survival, such as a camel's ability to withstand harsh environments.

Summary of Natural Selection Process

1. Individuals exhibit variation.

2. Traits are heredity-based and can be passed to offspring.

3. There are limited resources, leading to competition.

4. More offspring are produced than can survive, resulting in differential reproductive success.

Convergent and Divergent Evolution

• Analogous Structures: Traits evolve independently to fulfill similar functions (e.g., wings of birds vs. wings of insects).

• Embryological Similarities: Early embryonic stages show shared characteristics, suggesting common ancestry.

Conclusion

• Evolution is Continuous: The process of evolution through natural selection affects all populations, guiding how species adapt and survive across generations.