Origin of Life on Earth (Chemical Evolution of Life)

Life originated on earth through chemosynthesis or formation and coming together of biochemicals. It is called Naturalistic Theory or Theory of Chemical Origin of Life. The theory was given by Russian scientist Oparin (1924) and British turned Indian scientist J.B.S. Haldane (1929). 

According to the theory, life must have developed from the simple inorganic molecules which were present on earth soon after it was formed. He speculated that the conditions on earth at that time, which were far from the conditions we see today, could have given rise to more complex organic molecules that were necessary for life. The first primitive organisms would arise from further chemical synthesis. 

Experimental Proof

Stanley Lloyd Miller and Harold C. Urey (1953) assembled an apparatus to provide conditions similar to those of early earth. They took a mixture of ammonia, methane and hydrogen (2 : 2 : 1) and water at 800°C and exposed it to electric sparks, heating and cooling to resemble lightning and provide temperature just below 100°C. After one week, 15% of carbon from methane had been converted into organic compounds like sugars, organic acids, amino acids. The first primitive organism would arise from further chemical synthesis.

1.0Variations

Variations are the structural, functional or behavioral changes present between the members of a species or between parents and offsprings. There is an inbuilt tendency to variation during reproduction. Variations can occur both because of errors in DNA copying as a result of sexual reproduction and random segregation of alleles during gamete formation.

Variations provide raw materials for evolution. These may be inheritable or noninheritable, but only inheritable variation participates in evolution.

Variations are of two types:

(i) Somatogenic variations or acquired variations.

(ii) Germinal (blastogenic) variations.

Differences Between Somatogenic Variations and Germinal (Blastogenic) Variations

2.0Genetic Drift  

The change in the frequency of certain genes in a population over generations or the random changes in the gene frequency occurring by chance alone. The effect of genetic drift is very small in large population and large in small population. Genetic drift provides diversity without any adaptation.

In case of genetic drifts genes of individuals are passed on to the next generation irrespective of whether they can adapt to the environment or not.

An illustration: 

1. A group of twelve red beetles living in bushes with green leaves.

2. Beetles in the population can generate variations because these are reproducing sexually.

3. Crow can eat the beetles. The more beetles the crow eat, the fewer beetles are left for reproduction.

Now consider the following situations  

• Inherited characters are passed on to next generations as in these traits a change in DNA of germ cells takes place like eye colour, hair colour, shape of nose, height etc. Such characters are called germinal characters.

• Acquired traits or non-inherited characters are those characters which we develop in our lifetime like strong muscles, pierced ear, tattoos on body, hair cut patterns etc. These characters are not passed to next generation and these are called somatic characters as in these traits DNA of germ cells does not change.

3.0
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