Bio 9/2

Evolution: Core Ideas and Theories

  • Evolution is a unifying principle in biology, explaining life's diversity and adaptation.

  • Scientific Theory: An idea backed by scientific evidence, making testable predictions, which can be revised.

    • A robust theory explains observable phenomena, enables predictions, and accommodates new data.

    • Science benefits from falsification, refining ideas by proving them wrong.

    • Theories require high levels of consistency (e.g., >99\% of evidence supporting them).

Darwin, Wallace, and the Origins of Evolutionary Thought

  • Descent with Modification: Darwin's core idea that current species evolved from ancestral ones.

  • Natural Selection: Mechanism for evolution, emphasizing reproductive success (fitness).

    • Fitness: Best understood as reproductive success (number of offspring).

  • Darwin's Voyage (HMS Beagle):

    • Observed diverse environments (e.g., Galápagos Islands), noting island species resembled mainland but adapted locally.

    • Collected specimens, made geological and fossil observations.

  • Wallace: Independently conceived natural selection; prompted Darwin's joint publication in 1858 and On the Origin of Species in 1859.

  • The Origin of Species (1859): Outlined the unity, diversity, and adaptation of life.

Geological and Philosophical Foundations Behind Evolution

  • Gradualism (Hutton, 1795): Earth's features arise from slow, continuous changes.

  • Population Theory (Malthus-inspired): Population growth outpaces resources, leading to competition.

  • Uniformitarianism (Lyell, 1830): Present geological processes are the key to understanding past ones, implying a very old Earth.

    • Darwin used Lyell's ideas to support the timescale needed for gradual evolution, challenging the ~6,000-year old Earth concept.

  • Catastrophism (Cuvier): Major events cause rapid changes and extinctions.

  • Linnaeus and Taxonomy: Developed binomial nomenclature (e.g., Homo sapiens) for classifying organisms.

Mechanisms of Evolution: From Observation to Prediction

  • Adaptations: Heritable traits improving an organism's survival and reproduction in an environment (physical, behavioral, physiological).

  • Adaptation vs. Acclimation:

    • Adaptation: Heritable, persists across generations.

    • Acclimation: Short-term individual adjustment, not inherited.

  • Examples of Adaptations:

    • Desert Beetle: Water collection via leg hairs from fog, survival traits in arid environments.

    • Marine Iguanas (Galápagos):

    • Evolved to feed on cold-water algae; long dives and breath-holding capability.

    • Flattened tail and specialized claws for swimming and gripping.

    • Dark coloration for heat absorption, unique thermoregulation behaviors (ectotherm).