In this article we will discuss about:- 1. Chemical Hypothesis to the Origin of Life 2. Chemical Evolution of Life 3. Biological Evolution.
Chemical Hypothesis to the Origin of Life:
It is universally accepted that life arises from life and continuity is maintained. It is equally true that there was no trace of life on the earth at the time of its origin and naturally life had a beginning on this planet at a later date and that from non-living. The issue is a complex one and we can only make vague guesses.
All the life including the viruses has as its physical abode the nucleoproteins, highly complex organic compounds. Except some amino acids, synthetically prepared in the laboratory, the majority of the amino acids, constituents of nucleoproteins, are synthesized exclusively in the living organism.
Spontaneous origin of these energy- rich compounds is highly improbable, still attempts have been made to trace the origin of these substances without intervention of life. This is known as chemical hypothesis of the origin of life.
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For this we are to visualize a kind of simple virus capable of utilizing organic substances and multiply in an inorganic environment as a free living organism, unlike the parasitic viruses of the present day. The conditions which were prevalent on the earth when it was young, were entirely different from those of the present age, and they cannot be duplicated.
The high temperature permitted water to exist only in the form of superheated steam. There was no free oxygen or ozone in the atmosphere and high energy ultra violet radiation could reach the earth’s surface freely. With the cooling of the earth liquid water appeared and conditions were set for random compound formation and reformation.
Chemical Evolution of Life:
The most important elements — carbon, hydrogen, nitrogen and oxygen reacted with each other and with many other elements and countless compounds could be formed. Methane (CH4), the simplest organic compound was probably formed in such a situation. (Methane has been detected in the atmosphere of some cooler stars). Ammonia (NH3) was probably formed in such a way.
High energy ultraviolet radiations reached the earth’s surface and possibly simple aldehydes, such as formaldehyde (CH2O) appeared which could slowly condense into sugars. Organic acids also could be formed, and reacting with ammonia could give rise to other compounds, including simple amino acids, such as glycine (CH2NH2COOH). Protein could be formed by linking together several amino acids.
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These chemical compounds accumulated in large quantities in sea water, as there was no living organisms to consume them.
The sea water was still hot and it has been described as ‘The hot diluted soup’. Given enormous length of time, interaction between the simple organic molecules resulted in complex compounds like polysaccharides, fats, purines, pyrimidines, proteins, nucleosides and nucleotides.
A large number of nucleotides were linked together in different sequences resulting in nucleic acids. Nucleoproteins were formed by the union of nucleic acid and protein molecules. The nucleoprotein molecules were presumably comparable to free living genes. A number of them possibly aggregated to form protovirus.
Biological Evolution of Life:
The large molecules combined in various sequences and precipitated as colloid particles, termed Coacervates. These distinct bodies suspended in water possessed several types of proteins, nucleoproteins and other organic and inorganic molecules.
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Substances like lecithin and cephalin organised to form the limiting or surface membrane around the coacervates. Some of the proteins were transformed into enzymes, which could lead to new reactions. Gradually, the coacervates were surrounded by nutrient shell and living membrane, and the first living unit or cell was formed.
Of the early cell types, two are considered significant:
(a) Moneran type:
The nucleoproteins are arranged loosely in the cell substance. The bacteria and blue green algae evolved from them.
(b) Protistan type:
The nucleoproteins condensed into a mass, surrounded by a membrane and separated from the cell substance. They are ancestors of other organisms.
It may be emphasized that no direct evidences are available and any or none of these steps may be correct.