Evolution

• Origin of Life

  • Big Bang Theory
    • Origin of universe ($20$ billion years ago)
    • Expansion and cooling
  • Earth's Formation
    • Formed $\sim 4.5$ billion years ago
    • Primitive atmosphere: $CH_4, NH_3, H_2O, H_2$ (no free $O_2$)
  • Abiogenesis
    • Origin of life from non-living organic molecules
    • Panspermia: Spores transferred from other planets
  • Chemical Evolution
    • Proposed by Oparin and Haldane
    • Inorganic molecules $\rightarrow$ Organic monomers $\rightarrow$ Polymers
  • Miller's Experiment ($1953$)
    • Simulated primitive earth conditions
    • Synthesized amino acids from $CH_4, H_2, NH_3$, and water vapor at $800^\circ C$

• Evidences for Evolution

  • Paleontological Evidence
    • Study of fossils in sedimentary rocks
    • Connective links (e.g., Archaeopteryx between reptiles and birds)
  • Morphological & Anatomical Evidence
    • Homologous Organs
      • Same structure, different function
      • Indicates divergent evolution (e.g., whale flippers, bat wings, human hands)
    • Analogous Organs
      • Different structure, same function
      • Indicates convergent evolution (e.g., wings of butterfly and bird)
  • Biochemical Evidence
    • Similarities in proteins and genes (DNA, RNA)
  • Embryological Evidence
    • Proposed by Ernst Haeckel (Ontogeny recapitulates phylogeny - later modified)

• Theories of Evolution

  • Lamarckism (Theory of Inheritance of Acquired Characters)
    • Use and disuse of organs (e.g., Giraffe's neck)
  • Darwinism (Theory of Natural Selection)
    • Proposed by Charles Darwin (Voyage on HMS Beagle)
    • Key concepts: Overproduction, struggle for existence, variation, and survival of the fittest
    • Industrial melanism as a classic example
  • Mutation Theory
    • Proposed by Hugo de Vries
    • Single-step large mutations (saltation) drive evolution

• Modern Synthetic Theory

  • Combines Darwinism and genetics
  • Factors affecting allele frequencies:
    • Gene flow
    • Genetic drift (Founder effect and Bottleneck effect)
    • Mutations
    • Genetic recombination
    • Natural selection

• Hardy-Weinberg Principle

  • Allele frequencies in a population are stable and constant from generation to generation (genetic equilibrium)
  • Equation: $p^2 + 2pq + q^2 = 1$
  • Factors disturbing equilibrium: Gene migration, genetic drift, mutation, recombination, natural selection

• Brief Account of Evolution

  • Plant Evolution
    • Psilophyton $\rightarrow$ Ferns $\rightarrow$ Conifers $\rightarrow$ Flowering plants
  • Human Evolution
    • Dryopithecus $\rightarrow$ Ramapithecus $\rightarrow$ Australopithecus $\rightarrow$ Homo habilis $\rightarrow$ Homo erectus $\rightarrow$ Homo neanderthalensis $\rightarrow$ Homo sapiens