M12 BIO

Module 12: Evolution and Speciation

• Understanding Evolution

• Evolution: Change in heritable traits over generations.
  
  

• Sources of Variation:
  
  

  • Mutations: Random DNA changes (beneficial, neutral, harmful).
    
    

  • Sexual Reproduction: Shuffling genes.
    
    

  • Gene Flow: Alleles move between populations.
    
    

  • Genetic Drift: Random allele frequency changes (strong in small pops).
    
    

• Key Ideas:
  
  

  • Evolution isn’t goal-directed.
    
    

  • Complexity ≠ evolutionary “better.”
    
    

• Evidence for Evolution

• DNA Analysis: Genetic similarities.
  
  

• Fossils: Record of gradual changes.
  
  

• Homologous Structures: Same structure, different function (e.g., limbs).
  
  

• Vestigial Structures: Leftover traits (e.g., appendix).
  
  

• Formation of New Species (Speciation)

• Species: Group that interbreeds and produces fertile offspring.
  
  

• Speciation: Formation of new species through genetic isolation + divergence.
  
  

• Mechanisms of Speciation

• Allopatric ("different homeland"):
  
  

  • Geographic separation.
    
    

  • Caused by dispersal or vicariance.
    
    

• Sympatric ("same homeland"):
  
  

  • No physical barrier.
    
    

  • Often due to:
    
    

    • Polyploidy (extra chromosome sets) in plants.
      
      

    • Behavioral shifts or new ecological niches.
      
      

Adaptive Radiation

• Rapid speciation to fill different niches (e.g., Hawaiian honeycreepers).
  
  

Reproductive Isolation

• Prezygotic Barriers (before fertilization):
  
  

  • Temporal, habitat, behavioral, mechanical, gametic.
    
    

• Postzygotic Barriers (after fertilization):
  
  

  • Hybrid inviability, hybrid sterility, hybrid breakdown.
    
    

Reconnection and Speciation Rates

• Hybrid Zones:
  
  

  • Reinforcement, fusion, stability.
    
    

• Speciation Models:
  
  

  • Gradualism: Slow, steady changes.
    
    

  • Punctuated Equilibrium: Rapid change, long stability.