The Origin of Life: Concept, Approaches and Theories

In this article we will discuss about:- 1. Concept of the Origin of Life 2. Approaches of the Origin of Life 3. Theories.

Concept of the Origin of Life:

The origin of life on earth is one of the most elusive and oldest problems of bio­logy. For about one half of the long span of earth’s history, the earth was barren and lifeless. But at some indeterminate time the entity called life came into exis­tence.

What form it took and what circum­stances brought it into being remain ever a problematic issue. The attention of the keenest minds of science and philosophy tried to answer this question. From time immemorial several explanations have been put forward to explain this phenomenon. But recent researches and experimenta­tions have abandoned most of the expla­nations.

Approaches of the Origin of Life:

By the turn of this century several main approaches have been made on the origin of life. These approaches are the vitalism, special creation, panspermia, mechanistic theory and materialism.

1. Vitalism:

This concept attributes the distinctive properties of the living things to a supernatural life force.

2. Special Creation:

This concept is nothing but the literal interpretation of the Biblical aspects of genesis.

3. Panspermia:

By assuming the eternal and universal existence of life, this concept avoids the question of the origin of life on this earth.

These three ideas regarding the origin of life, viz., vitalism, special creation and panspermia, need no detailed considera­tion, because they are based on assump­tion without having any scientific back­ground. But the other two theories, the mechanistic theory and the materialistic, doctrine need tremendous consideration.

Theories of the Origin of Life:

1. Mechanistic Theories:

These theories are based on the assumption that (i) the origin and activities of living things are derived from natural laws and (ii) that the living things are derived from inorga­nic matters in accordance with those natural laws. But these ideas were con­fronted with serious difficulties.

The real potent question is how can a living thing be formed from inorganic matters? These theories believed that the earth was total­ly devoid of organic compounds in pre-biological days arid that only living organisms can produce organic com­pounds.

The organic compounds cons­titute the most vital part of the living or­ganisms and as such their origin in the absence of organic compounds remains a formidable problem for ever.

The mechanistic theories resolved that the first living thing was a macromolecule or “living molecule” that was originated by the accidental coming together of the components that composed the living molecule in appropriate and proper arrangements and proportions.

It is also believed that the living molecule was probably a molecule of protein—the most important part of the living things. The mechanistic concepts advocate the origin of first living things by the chance combi­nation of these elements. This has come about by trail and error through an enor­mously long span of time.

2. Materialistic Theories:

These theories hold a different view by applying the natural laws to explain the origin of life and reject the contention of the mechanistic theories that only living things can synthesise organic compounds. On the contrary these theories propose that the organic compounds were formed abiogenecally, (i.e. without the intervention of living things) prior to the living organisms came into existence.

Instead of an acci­dental get-together of the elements to produce living things all at once as advo­cated in mechanistic doctrine, materialis­tic theories advocate the origin of life as result of series of steps towards increas­ing complexities and eventually leading up to the living state.

One of the most important steps is the abiogenic synthesis of the organic ‘compounds. Every step leads into a higher grade of organisation of matter that did not exist at the lower level. With the gradual formation of molecules, new physical as well as chemi­cal properties appeared in the scene which were non-existing in the realm of uncombined elements.

By this way and with the advent of living organisms, biological laws came into operation which did not exist before. The materialistic theories hold that the origin of life was not an accident, but it was the end result of matters evolving into higher and higher forms step by step.

Evolution of living things from non-living matters was the speculation of the thinkers of the past. To name a few, they were F. Engels, H. Spencer, T. H. Huxley, C. Mitchell and E. A. Schafer. F. Engels in his “Dialectics of Nature” condemned the concept of the spontaneous generation and vitalism and maintained that the living things have originated from a continuous evolution of matters.

A Russian Biochemist, A. I. Oparin in 1922, holds that the organic compounds had existed on the earth before the origin of living things and the living things have evolved from these pre-existing compounds.

He views the evolutionary sequences (such as the formation of inorganic compounds, organic compounds, primitive and higher living things) not as separate events, but as merely the steps in the process of un­folding of the same biological process.

J. B. S. Haldane in 1928 was also of the opinion of the abiogenic formation of organic substances in the prebiological history of the earth. He postulated that the organic compounds must have accu­mulated before the origin of life.

He assumed that the primitive atmos­phere contained only carbon dioxide, ammonia and water vapour. There was no oxygen. Haldane was of the opinion that such a combination, exposed to ultra­violet light, can evolve into a large variety of organic compounds.

Oparin’s Hypothesis:

In his attempt to solve the problem of the origin of organic compounds on this earth, Oparin based his concept on the then accepted theory on the origin of earth proposed by Sir James Jeans. Although Sir Jean’s theory of the fiery origin of the planets is no longer acceptable, it provided a basis for the formulation of Oparin’s theory of the origin of organic compounds on the earth.

Oparin assumes that the first carbon compounds were the hydrocarbons and not the carbon dioxide. To put the question in other way, he assumes the first appearance of carbon in the reduced state and not in the oxidised state because the pri­mordial atmosphere was devoid of oxygen.

With the cooling down of the atmosphere to 1000°C. and lower, the highly reactive free radicals (viz. CH and CH₂) combined to produce a variety of simple saturated and unsaturated hydrocarbons.

The crust of the earth had begun to form but the temperature was still too hot to allow condensation of steam to water. But the atmosphere above the crust contained carbon as well as nitrogen in reduced state. The reduced state of carbon was the hydrocarbons while that of nitrogen was ammonia. Such reducing atmosphere forms the basis of Oparin’s theory of the origin of life.

The simplest substances, such as hydro­gen, steam, methane, hydrogen sulfide, ammonia and nitrogen are continuously producing simple hydrocarbons and their derivatives—the alcohols, aldehydes, sugars, ketones and acids.

Of the deriva­tives there are the amino-acids and the polymerisation of the amino-acids results in the formation of protein. The mole­cules of protein have the capability of coming together and form large complexes. By this way colloidal hydrophilic com­plexes are produced and these complexes play the active role in the transformation of inanimate things into living systems.