Evolution: Fact vs Theory Review

Evolution: Fact vs Theory

  • Facts

    • Observations about the world.

  • Hypothesis

    • Proposed explanations for phenomena; unproven; requires testing.

  • Theory

    • Well-tested explanations confirmed through observation and experimentation.

  • Law

    • Detailed mathematical descriptions of how events occur.
    • Laws do NOT explain why phenomena occur.

  • Science is Constantly Evolving

    • Scientific knowledge is subject to change as new data emerges.

Key Concepts in Evolution

  • Evolution

    • Refers to changes in populations over time.

  • Charles Darwin (1859)

    • Published The Origin of Species explaining natural selection based evolution.
    • Served as a naturalist on the HMS Beagle expedition.
    • Observed fossils of extinct animals and variations among species in South America and the Galapagos Islands.
Natural Selection
  • Natural Variations
    • Inherent differences among individuals exist; these are adaptations.
  • Adaptations
    • Favorable adaptations increase in frequency in populations.
  • Gene Pool Changes
    • Population changes favor the fittest phenotypes/genotypes.
  • Competition for Resources
    • Only the best-suited organisms survive and reproduce.
  • Survival of the Fittest
    • Some phenotypes are better suited for competing for resources, leading to survival and reproduction.
Results of Natural Selection
  1. Directional Selection
    • One phenotype replaces another due to environmental changes.
    • Example: Peppered moths, antibiotic resistance.
  2. Diversifying (Disruptive) Selection
    • Individuals at extremes have higher fitness than average individuals.
    • Example: Darwin's finches.
  3. Stabilizing Selection
    • Average traits are favored and extremes are reduced.
    • Example: Human birth weights.

Evidence of Evolution

  1. Fossil Record
    • Fossils represent biological history; comparing layers shows life has changed over time through sedimentary rock strata.
  2. Geographic Distribution
    • Species descended from common ancestors, leading to adaptive radiation.
    • Adaptive Radiation: Diversely adapted species evolve from a common ancestor, especially in varied environments.
  3. Similarities in Early Development
    • Common embryonic pathways among vertebrates, indicating common ancestry.
  4. Genetic Evidence
    • All life shares basic genetic machinery (RNA/DNA); the genetic code is nearly universal.
    • Sources of Genetic Variation:
      • Mutations
      • Sexual reproduction
      • Crossing over (Prophase I)
  5. Comparative Morphology
    • Homologous Structures: Similar embryonic tissues, differing adult forms; indicates common ancestry.
    • Analogous Structures: Similar functions due to environmental pressures, not common ancestry.
Vestigial Organs
  • Organs reduced in size with no current function, indicating common ancestry.
    • Examples in Humans: Wisdom teeth, coccyx, appendix, reduced little toe.

Mechanisms of Evolution

  • Changes in allele frequencies might arise from:
  1. Genetic Mutations
    • Errors in DNA replication lead to variation.
  2. Gene Flow
    • Introduction or exit of alleles between populations (immigration/emigration).
  3. Genetic Drift
    • Random fluctuations in allele frequencies due to chance events.
  4. Natural Selection
    • Differential reproduction based on traits; favorable traits increase in frequency.

Patterns of Evolution

  1. Divergent Evolution

    • Related species diverge into different forms.
    • Example: MammALS diverging from a common ancestor.

  2. Convergent Evolution

    • Unrelated species develop similar traits due to analogous traits.
    • Example: Wings of butterflies, birds, bats.

  3. Coevolution

    • Mutual adaptations occurring in closely interacting species.
    • Example: Bumblebees and flowers.

  4. Microevolution

    • Evolution within a population; small adaptive changes.

  5. Macroevolution

    • Large-scale changes leading to speciation.
Speciation Process
  • Interrupting gene flow leads to accumulation of genetic differences, eventually leading to reproductive isolation.

Rates of Evolution

  1. Gradualism
    • Slow, steady changes over time.
  2. Punctuated Equilibrium
    • Periods of rapid change interspersed with stability.

Cladograms

  • Cladograms visualize the evolutionary relationships and speciation events among species.
  • Key Factors in interpreting cladograms include shared characteristics, branching patterns, and species relationships.

Relevant Practice and Examples

  • For understanding evolutionary concepts, examining illustrations and data on limbs and fossils helps recognize common ancestry and evolutionary trends among species.