Ch 14: Evolution, Medicine, & Society

Origins of Darwin's Theory

• Key Figures:

  • Jean-Baptiste Lamarck ($1744-1829$):

    • An early evolutionary thinker who proposed the first cohesive theory of biological evolution.

    • Inheritance of Acquired Characteristics: Lamarck hypothesized that physiological changes acquired during an organism's life (such as a giraffe stretching its neck to reach higher leaves) could be passed down to offspring.

    • Use and Disuse: Suggested that parts of the body used extensively become larger and stronger, while those not used deteriorate.

  • Charles Darwin ($1809-1882$):

    • Developed the theory of evolution by natural selection after observing diverse flora and fauna during his five-year voyage on the HMS Beagle.

    • Influenced by Thomas Malthus, who argued that populations grow faster than resources, leading to a "struggle for existence."

• Earlier Ideas and Influences:

  • Creationism (Special Creation): The prevailing belief that species were created individually by a divine being and remained immutable (unchanging) over time.

  • Transmutation: A precursor to the modern concept of evolution; it proposed that one species could transform into another through natural processes, though it lacked a clear mechanism like natural selection.

  • Lamarckianism vs. Darwinism: While Lamarck focused on individual effort and use/disuse, Darwin focused on inherent variation within a population and the survival of those best adapted to their environment.

  • Uniformitarianism: Principles from geologists like Charles Lyell suggested that the Earth was much older than previously thought ( > 6,000 years), providing the necessary deep time for evolution to occur.

On the Origin of Species

• The Publication of a Breakthrough ($1859$):

  • Darwin delayed publication for nearly $20$ years until he received a manuscript from Wallace that mirrored his own findings.

• Co-discoverers of Evolution by Natural Selection:

  • Alfred Russel Wallace: Independently conceived the theory of natural selection while working in the Malay Archipelago.

  • Joint Presentation ($1858$): Their ideas were presented together at the Linnean Society of London, marking the formal introduction of the theory to the scientific community.

• Three Observations of Natural Selection:

  1. Variation: Individuals within a population vary in their traits.

  2. Inheritance: Some of these variations are passed on to offspring.

  3. Differential Reproductive Success: Individuals with traits better suited to their environment are more likely to survive and reproduce.

Mis-use of Darwin's Ideas

• Survival of the Fittest:

  • Coined by Herbert Spencer, not Darwin. In a biological sense, "fitness" refers to reproductive success (the number of offspring an individual leaves behind), but it was incorrectly used to describe physical strength or social dominance.

• Social Darwinism:

  • An attempt to apply the concepts of natural selection to human socioeconomic structures.

  • It argued that the "strong" (wealthy/powerful) should see their wealth and power increase, while the "weak" should see their wealth and power decrease.

  • Used to justify colonialism, laissez-faire capitalism, and racial hierarchies.

• Eugenics:

  • Termed by Francis Galton, a cousin of Darwin.

  • A movement advocating for the improvement of the human species by encouraging breeding of people with "desirable" traits and discouraging or preventing the breeding of those with "undesirable" traits.

  • Led to unethical practices, including forced sterilization and the Nuremberg Laws in Nazi Germany.

Quote on Evolution

• Theodosius Dobzhansky ($1900-1975$):

  • "Nothing in biology makes sense except in the light of evolution."

  • Dobzhansky was a central figure in the Modern Synthesis, which unified Darwinian natural selection with Mendelian genetics.

  • This quote highlights that evolution is the overarching framework that connects disparate fields like anatomy, genetics, and medicine.