BIO112 Lec7 Evolutionary Processes 1 2025

Evolution in Action

  • Contemporary Evolution

    • Refers to observable instances of evolution occurring in real time.

    • Examples include:

      • Drug Resistance: Evolution of resistance in pathogens such as bacteria (e.g., MRSA resistant to vancomycin).

      • Pesticide Resistance: Insects evolving resistance to chemical pesticides.

      • Fishing Effects: Changes in fish populations due to selective harvesting practices.

    • Notable example: Darwin's Finches on the Galápagos Islands provide evidence of natural selection.

Human-Induced Evolution

  • Unnatural Selection:

    • Occurs through the hunting and fishing of animals for desirable traits.

    • This differs from agriculture, where breeding is controlled to enhance desirable traits.

    • Potential effects include:

      • Reduction in desirable traits (e.g., larger body size in fish) due to selective harvest.

      • Possible changes in mating systems that alter sexual selection, impacting species' sustainability.

    • Consequences of Harvest:

      • Can lead to undesirable evolutionary changes (e.g., smaller body sizes, quicker maturity rates).

      • 'Unnatural Selection': Imposed by human activities, often counterproductive to conservation goals.

Traits Affected by Unnatural Selection in Harvested Populations

  • Common Traits Affected:

    • Age and Size at Maturity:

      • Increases in mortality from harvesting lead to earlier sexual maturity.

      • Changes in the general body size due to selective pressure for larger individuals.

    • Body Size and Morphology:

      • Traits such as antlers or tusks may be diminished due to trophy hunting.

    • Reproductive Timing and Behavior:

      • Harvest can skew the timing of reproduction and alter behavioral traits.

    • Migration Patterns:

      • Altered due to selective pressure on individuals showing predictable patterns.

    • Remedies Suggested:

      • Modify harvest practices to support genetic diversity (adaptive management).

Natural Experiments in Evolution

  • Case Study of Medium Ground Finch (Geospiza fortis):

    • Location: Daphne Major, Galápagos Islands.

    • Research Question: Did drought-driven environmental changes affect finch beak characteristics?

    • Hypothesis: Changes in beak depth in response to drought conditions.

    • Methodology: Weigh and measure finches pre- and post-drought to assess changes.

Finches Data Summary

  • Population Dynamics:

    • Example data showing population size and average beak depth across years.

    • Observed Results:

      • Beak depth increased significantly in survivors post-drought.

Common Misconceptions about Evolution

  • Misconception 1: "Evolutionary change occurs in organisms"

    • Correction: Natural selection works on existing variants; evolution occurs in populations.

  • Misconception 2: "Evolution is goal directed"

    • Correction: Adaptations arise by chance, not through the organism's intention to evolve.

  • Misconception 3: "Evolution perfects organisms"

    • Correction: Not all traits are adaptive; some traits may not optimize due to trade-offs or constraints.

Hardy-Weinberg Principle

  • Definition: Describes allele and genotype frequencies in a population under specific conditions.

  • Basic assumptions include:

    • Random mating, no selection pressures, no genetic drift, no gene flow, and no mutation.

  • Equations:

    • Allele frequency equation: p + q = 1.

    • Genotype frequency equation: p² + 2pq + q² = 1.

  • Implication: Evolution requires deviations from these conditions for change.

Case Study: MN Blood Types in Humans

  • Analysis Steps:

    1. Estimate genotype frequencies.

    2. Calculate observed allele frequencies from genotype analysis.

    3. Determine expected genotype frequencies based on Hardy-Weinberg.

    4. Compare observed and expected data for population evolution assessments.