Theories of Origin of Life Short Notes | Evolution Class 12 Notes

In this article we will discuss about Theories of Origin of Life :- Theory of special creation, Theory of abiogenesis, Theory of biogenesis, Theory of panspermia and Chemogenetic Theory

THEORIES OF ORIGIN OF LIFE

• Several attempts have been made from time to time to explain the origin of life on earth
  1. Theory of special creation
  2. Theory of abiogenesis
  3. Theory of biogenesis
  4. Theory of panspermia
  5. Chemogenetic Theory

1. Theory of special creation

• This is mythology based theory
• All the living beings on earth were created by god
• Hindu mythology: Lord Brahma is creator of the living world, He create all the living and non living things in the world
• Christian mythology: God creates the earth and puts adam and eve, they are first humans in the world

2. Theory of abiogenesis

• It is also called spontaneous generation or autobiogenesis
• Supporters :- Aristotle, Epicurus and Von Helmont
• They believed
  • Insects arise from dew
  • Fish & frog from mud
  • Fly maggots from meat
• Opposers :- Fransisco Redi, Spallanzani amd Louis pasteur

3. Theory of biogenesis

• Living organisms are always produced from pre-existing living forms by reproduction and not from non-living or lifeless matter
• This theory could not explain first life on earth
• Experiments of Fransisco Redi, Spallanzani amd Louis pasteur etc supported the theory of biogenesis

4. Theory of panspermia

• Proposed by Richter in 1865
• Life on earth came from different planet in the form of spores or microorganisms
• This is called cosmozoa or panspermia which were preserved inside meteorites
• These meteorites struck into barren earth to release cosmozoa and help in development of various creature

5. Chemogenetic Theory

• The Chemogenetic theory was
  • Proposed by Oparin & Haldane (1924)
  • Evidence provided by Urey & Miller (1953)
• Chemogenetic Theory divided into three parts: Chemogeny, Biogeny and Cogenogeny

I) Chemogeny

• Primitive contition of earth: High temprature, Volcanic storms and lightening
• Primitive earth contain large amount of H, N, C and few O
• Hydrogen reacted with other atoms to from a variety of molecules
  • Ammonia: Hydrogen + Nitrogen
  • Methane: Hydrogen + carbon
  • Water: Hydrogen + oxygen
• Earth cooled down, water vapour fell as rain and form primitive ocean
• During this molecules continued to react with each other and formed various Simple chemical compounds formed
• E.g. Sugars, Aldehyde, N2 Base, Fatty acid
• Water of oceans became rich mixture of chemical compounds. its called pre biotic soup

II) Biogeny

• Next step is formation of Biomolecules.
• The hot dilute soup was sterile and oxygen free
• Simple organic compound come together, form colloids to form complex compound like polysaccharides, protiens, nucleosides, fats and nucleotides.
• The protein molecules formed by polymerization of amino acids (protoprotein)

III) Cogenogeny

• Macromolecules formed by the polymerization of micromolecules underwent precipitation in the sea
• Precipitation resulted in the aggregation of macro molecules
• The aggregation resulted in formation of organized structures
• These organized structures can be called as coacervates
• Smaller coacervates fused together to form larger coacervates
• Coacervates were behave like living molecule
• Oparin suggested that coacervates may give rise to cell like structures
  formation of life