What Is Evolution?

The context of the origin of life, i.e., the evolution of the earth, of stars, and indeed of the universe itself. To unfold or unroll or reveal the hidden potentialities is called evolution. Evolution is an orderly change from one condition to another. Evolution is a slow, gradual and continuous, or irreversible process. Evolution term was introduced by "Herbert Spencer". Evolution   can be best explained by Darwin's concept of "Descent with Modification"
Descent= Next generation or Modification = Changes. 


What is Evolutionary Biology?

Evolutionary Biology is the study of the history of life forms. i.e. the changes in flora(plants) and fauna(animals) that have occurred over millions of years on earth.

What is Universe? 

The universe is a huge cluster(group) of galaxies. Galaxies contain stars and clouds of gases and dust. Considering the size of the universe earth is indeed a speck(tiny particle). i.e. the universe is vast. Milky Way is a very small part of the universe. So when we see stars we apparently are peeping into the past. 


Big Bang Theory

This theory s proposed by "Abbe Lemaitre". The universe originated about 20 billion years ago (bya) due to a thermonuclear explosion of a dense entity. This single huge explosion which is unimaginable in physical terms is called Big Bang.

  • Earth formed – 4.5 Billion Years Ago
  • There was no atmosphere on early earth.  


Theories for origin of life 

  1. Theory of special creation
  2. Cosmic Panspermia 
  3. Spontaneous(suddenly) generation theory
  4. Biogenesis Theory 
  5. Oparin Haldane Theory

Special Creation theory 

This theory was supported by father Suarez. This is a mythological theory. All living organisms that we see today were created as such. Diversity was always the same since its creation and will be the same in the future. According to this theory, Life originates in 6 days. According to this earth is about 4000 years old.


Cosmic Panspermia Theory 

This theory was supported by Early Greek Thinkers/ Ritcher. Some scientists believe that life came from outer space. Early Greek thinkers thought units of life called spores were transferred to different planets including earth. ‘Panspermia’ is still a favorite idea for some astronomers.

Theory of Spontaneous generation 

Also known as Abiogenesis(non-living formation)/Autogenesis theory. 

Non-living matter➡ Living Organisms




Theory of Biogenesis 


Also known as the theory of living. Proposed by Harvey and Huxley.
“Omnis vivum ex ovo or Vivo” means (life came from pre-existing life) 
Living Organisms ➡ Living Organisms
To prove biogenesis or disprove abiogenesis Louis pasture did a "Swan Neck Experiment"


Oparin – Haldane Theory

Also known as the Theory of chemical evolution. Proposed by Oparin and Haldane.
Inorganic constituents ➡ Diverse organic molecules
Non-living organic molecules (RNA, Protein, etc.) ➡ First Life

  • First life originated in seawater, so WATER is essential for the origin of life. 

Part – A Chemical Evolution

  1. ATOMIC STAGE (C, H, O, N )
  2. MOLECULAR STAGE (H2O(g), NH3, CO, CO2, N2, H2, CH4 )
  3. SIMPLE ORGANIC COMPOUNDS (Aldehydes, Ketones, Pentose, Hexose, Amino acids, Fatty acids, Glycerols, Nitrogenous bases)  
  4. COMPLEX ORGANIC COMPOUNDS (Proteins, Carbohydrates, Lipids, Nucleic acids) 
  • Water and ammonia were probably the first inorganic compounds formed on earth.
  • Methane (𝑪𝑯𝟒) was the first organic compound.
  • No free oxygen (O2 ) was left, which made the atmosphere reduce.
  • The primitive conditions on earth were
1. High temperature 
2. Volcanic storms 
3. Lightening 
4. Radiation 
5. Reducing atmosphere  


Evidence in favor of chemical evolution  

(1) Urey & Miller Experiment (1953): 


(2) Evidence from meteorites: 
A sample of the Murchison meteorite that fell on Murchison, Australia, on September 28, 1989, is shown here. This meteorite is rich in carbon, purines, and pyrimidines.  


Part – B Biological Evolution  

Protobionts

  1. Clusters of macromolecules
  2. Colloidal drop like structures
  3. Show growth
  4. Exhibit simple metabolism
  5. Partially isolated from the external environment i.e. they were able to maintain their constant internal environment 
  6. Lipid membrane absent.
  7. Could not reproduce 
  • NOTE: Artificially synthesized protobionts 
  1. Coacervates by Oparin
  2. Microspheres by Sydney Fox
Nucleic acid + Proteins → Nucleoproteins (First sign of life) 

Eobionts (Protocell) 


  • Clusters of nucleoproteins surrounded by lipid coat
  • First living form
  • First self-replicating capsules
  • Origin 3 Billion Years ago
  • First Non-cellular form of Life 
  • Energy by glucose fermentation
  • Virus-Like Structures Retrogressive evolution 

First Prokaryotic cell  

  • Cellular form of Life
  • Origin 2 Billion Years ago
  • Single-celled and reproduce
  1. By budding 
  2. By binary fission
  • Anaerobic 
  •  Chemoheterotphs

Prokaryotic cells 

  • Chemoheterotrophs & Anaerobes (Absorbed organic molecules from surroundings)
⬇(Mutation)
  •  Chemoautotrophs & Anaerobes
(Inorganic matter → Organic food)) 


⬇(Mutation)


  • Non-oxygenic photoautotrophs & Anaerobes 
(Source of Hydrogen – H2 S)

⬇(Mutation)

  • Oxygenic photoautotrophs & Anaerobes 
(Source of Hydrogen – H2O)  

Ex:- Cyanobacteria (BGA)








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