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Evidence of Evolution

  • Evolutionary evidence includes several forms:
    • Fossil record
    • Transitional fossils
    • Extinction
    • Biogeographical evidence
    • Vestigial structures

Vestigial Structures

  • Definition: Structures that are rudimentary and currently functionless in descendants, but were functional in a common ancestor.
  • Importance: Serve as evidence of evolution by showing modifications over time.

Examples of Vestigial Structures

  1. Blind Cave Organisms:

    • Mexican Tetra fish has functional eyes, while blind cave tetras exhibit rudimentary eye structures that no longer serve a purpose.
    • In dark cave environments, eyesight is not necessary, leading to evolutionary loss of eyes as it is energetically costly to maintain.

  2. Cave Salamander:

    • Similar to the blind tetra, exhibiting rudimentary eyes that are non-functional.

  3. Flightless Birds:

    • Examples include:
      • Dodo Bird: Small wings not used for flying; primarily walked.
      • Flightless Cormorant: Found in the Galapagos, with reduced wings.
      • King Penguin: Has vestigial wings, used for swimming, not flying.
      • Cassowary: A large bird with vestigial wings, found in Papua New Guinea and Australia.
    • Flightlessness in island birds often due to lack of predators, leading to reduced need for flight.

Characteristics of Vestigial Structures

  • Must be both rudimentary and non-functional to be classified as vestigial.
  • Examples in humans include:
    1. Goosebumps: Muscles contract causing hairs to stand; ancestral function was to appear larger against predators.
    2. Tailbone: Residual vertebrae from a tail, non-functional in humans.
    3. Appendix: Reduced from earlier functions, now less critical but serves some immune role.
    4. Wisdom Teeth: Once necessary for grinding raw plant material, now often non-functional due to jaw size changes in humans.

Homologous Traits

  • Definition: Traits shared by two or more species inherited from a common ancestor.
  • Types of Homology:
    1. Structural Homology: Similar physical structures modified for different functions.
    • Examples: Forelimbs of humans (grabbing), whales (swimming), bats (flying), cats (walking) show a common skeletal structure (humerus, radius, ulna).
    1. Developmental Homology: Similarities during early embryonic development despite adult differences.
    • Example: Pharyngeal pouches in vertebrate embryos resemble fish gills; similarities seen across embryos (chicken, human).
    1. Molecular Homology: Genetic similarities across species, including shared codons in genetic codes, indicating common ancestry.

Direct Observation of Evolutionary Changes

  • Evolution can be directly observed in organisms with rapid reproductive cycles.

  • Classic Examples:

    1. Antibiotic Resistance in Bacteria:
    • Bacteria exposed to antibiotics show survival of resistant varieties, leading to populations dominated by resistant bacteria after only a few generations.
    • Study linking antibiotic prescriptions to rising resistance rates in Finland from 1978 to the early '90s, showing a positive correlation.
    1. Resistance in Agricultural Pests:
    • Over application of insecticides leads to increased resistance in pests, rendering chemicals less effective.

Preparing for Future Topics

  • Upcoming discussions will cover:
    • Population genetics and evolutionary mechanisms.
    • Key concepts include:
    • Hardy-Weinberg Equilibrium: A model to determine allele frequencies in a population, assessing evolutionary changes.
  • Review core definitions related to genetics:
    • Gene: Functional unit of heredity.
    • Allele: Alternate forms of genes.
    • Genotype: Genetic makeup of an individual; essential in measuring evolutionary progress through allele changes.

Conclusion

  • Students are encouraged to review lecture materials as preparation for quizzes and understand the concepts of evolution, natural selection, and the genetic principles underlying them.
  • Critical to observe changes in allele frequencies to ascertain if evolution is occurring within species over time.
  • Instructions provided to watch supplementary videos for deeper comprehension of Hardy-Weinberg calculations.