By Raj Kumar


Various questions are popping almost in every human being regarding the origin of life, the existence of organisms on earth, how life originate? who were the first organisms? how organisms evolve? why are there are so many varieties in species? all these questions encourage us to look back to history and try to understand the possible ways in which try to figure out the possible method or theory to give a possible explanation regarding the origin of life, man, and evolution. Theories regarding origin of life. Various theories try to explain the origin of life some are mention below:

1. Life has always existed either on this planet or somewhere on another planet or stars in the universe in
the past. This theory explains that life and the universe were always there, but the scientific view
explains that the universe has also had its birth date so the theory was not accepted.

2. At some point in time in the past, some external being maybe God created the earth and the life
forms. This theory states that life may be created by some supernatural thing say, God. This theory or
hypothesis is the outcome of religion. Religion tells the origin of life by God.

3. At some point in time life originated on its own. This hypothesis states that life originated from the
atoms which aggregated and form the various life forms. Out of these theories or hypotheses, the 3rd hypothesis was widely accepted.

Before explaining the origin of life, let’s try to understand the origin of the universe. The most widely accepted theory regarding the origin of the universe was the “ Big Bang Theory”. this theory tries to explain the origin of the universe. This theory states that there was a huge explosion and expansion in an atomic or microscopical level material of hot primordial matter firstly form the universe by forming different types of galaxies, stars and then forms the earth which takes millions of years for its formation.

According to Big Bang theory, the origin of the universe dates back to some 20 billion years ago, and with its continuing explosion of the stars and the sun forms the earth around 4.5 billion years ago the earth form was a hot matter at that time.

The proton, neutron, and the electron associate and forms the atom, the atoms associate and forms the heavy nucleus, and with the formation of atoms with the nucleus, forms the light forms of gasses like helium, hydrogen, etc. Due to the supernova radiation, the earth was very hot and was in a molten state due to this heavy elements melt and went into the earth center whereas the lighter elements came above the earth surface, and because of these transformations different layers of the earth form I.e., the crust, mantle, and the core.

Theory of Spontaneous Generation

The theory of spontaneous generation was widely accepted regarding the origin of life but with some modifications. Earlier it was believed that life originates its own and in support of this, people say that if we mix different substances and left them open, the flies will originate after some time. They also supported it by saying that if clothes wet with sweat are left open, different types of microorganisms and flies will originate. But these views were discarded by Louis posture, who says that life does not originate from its own, it originates only if there already exists a life.

Some people also gave an opinion that life comes from interstellar space but this was also rejected as in the interstellar space there is no life-supporting environment and how it mas migrated to earth.

The theory of spontaneous generation was later modified by Russian scientist Oparin and England scientist Haldane. They proposed that the earth’s initial environment was the life-supporting environment.

They say that in the primitive environment of earth, the conditions for the origin of life were available and these conditions are not possible today I.e., life cannot develop on its own today. This is because during the initial stages of earth, the molecular oxygen which is present today was not developed at that time and due to the presence of molecular oxygen today, it degrades the molecular reaction which is necessary for the development of life.

They proposed that life originated at that time by chemical evolution which preceded the organic evolution, that is evolution from atomic to molecular, then to macro-molecular, and then organic evolution. And this transformation was supported by the conditions present at that time due to the absence of O2 gas and which are not possible ( as there is the presence of O2 gas today which breaks the evolution from atom to molecule, and molecule to macromolecule and due to this life will not originate), as the process of oxidation is present today.

According to chemical-organic evolution, simple inorganic precursor forms the simple organic compounds which then form the complex organic compounds which later develop the life, As the earth in its initial stage has substances in its atomic state and with the presence of the sun’s UV radiation these atomic substances react and form heavy atoms.

With the cooling of the earth, the elements like hydrogen, nitrogen, carbon reacted and form the complex molecules forming water, ammonia methane, etc which are called simple molecules and with the lightening on these molecules, these molecules reacted and form the complex molecules which are the building material like the today’s nucleic acids, etc which later aggregates and form the micro-spheres or the coacervates which tend to divide by using the organic or inorganic molecules or ions as food and started aggregating and form the proto-cell which came 3 billion years ago and the cell came about 2 billion years ago.

The theory given by Oparin and Haldane was supported by Miller in 1952 by creating an experimental design and creating the primitive environmental conditions of earth in the laboratory.

He found that by the combination of ammonia, water, carbon dioxide, and hydrogen, ammonia is formed which suggests that by the reaction of simple molecules, complex molecules can be formed.


The process of evolution is proposed by various theories and authors, out of which one theory was proposed by Jean-Baptiste Lamarck (1744-1829).

Lamarck argued that species evolved over time and primarily focused on two things:

1. If any animal made frequent use of any organ, it gradually straightens that organ while its disuse makes the organ weaken and finally disappear.

2. All acquired characteristics by an organism are preserved and passed on to the offsprings. But the work was incomplete and incorrect as the characteristics acquired and preserved by an organism did not pass into the off-springs and the offspring when born has to acquire the characteristics.

Another popular theory was proposed by Charles Darwin. Charles Darwin (1809-1882) was born in England. His father wanted him to become a doctor but Darwin wanted to be a naturalist. Lyell’s “principal of Geology” greatly impacted Darwin, which explains the origin and modification of earth. Charles Darwin, in his book “origin of species” describes the process of evolution.

It was a recollection of his experiences and evidence which Charles Darwin collected on Galapagos island
during his five-year survey on a ship called HMS Beagle. Darwin witnessed a wide variety of species, of particular importance, were Darwin’s finches, a set of bird specimens that brought back with him to England. When famous ornithologist John Gould inspected specimens, he concluded that they were the varieties of the same species of finches, Which causes Darwin to surprise as the birds differed so much in appearance and habits. Some had small beaks for eating insects while some have big beaks for crushing seeds and there was a range of variation in size. After returning from the voyage Darwin begins to assemble his enormous pile of observation and experiences into a theory. He found that the birds of Galapagos island shared a common ancestry. But the question of varieties and evolution made Darwin figure out the possible solution.

Darwin  Theory of Evolution

Darwin’s theory of evolution is based on natural selection due to which the theory is also known as
the theory of natural selection. It is based on five major features:
1. Over reproduction
2. Struggle for existence
3. Variation and heredity
4. Natural selection or survival of the fittest
5. Formation of new species :

Over reproduction: There is always a tendency of over reproduction in a species which helps the species in adjustment to their environment.

Struggle for existence: there is always a competition among the individuals in species for food, space, and other necessaries of life which Darwin called the struggle for existence. This struggle may be of three categories, which are given below:

1) Intra-specific struggle: the struggle between the individuals of the same species having similar needs.

(ii) Inter-specific struggle: struggle among the member of different species.

(iii) Environmental struggle: struggle against the extreme forces of nature.

Variation and heredity: all individuals of species are not 100% alike, nature will select only those organisms for continuity in the future who equip themselves to survive in a particular environment.

Artificial and Natural Selection: Darwin was a member of the pigeon club and conducted several experiments on pigeons. He concluded from his experiments that species change over generations and some of the characteristics were on high chance to pass from parents to springs. He proposed that man can master selective breeding by randomly breeding the organisms and select the organisms with the desired or the required traits out of the population which he calls Artificial Selection. But the question arises who selects in nature?
The answer to this question comes from Thomas Malthus (1766-1834) book “ Essay of the Principle of
Population” which proposed that species multiply at a rapid rate while the necessities such as food, shelter, water, etc, are limited.

Then the unlimited population struggle for the limited resources is called the struggle for existence. This struggle causes the population to live which are adaptable and fit to survive while those who are not, eliminate. This selection by nature is called as Theory of Natural Selection. This means that the selection will be done by nature and only those species survive which adapt themselves according to the environment which Darwin called evolution.

Formation of new species: continuation and accumulation of variations produce a new and different type which leads to the creation of new species which Darwin called the origin of species. Despite an immense contribution in the field of evolution Darwin also faced many objections which are due to the reason that he fails to explain some of the existing phenomena of evolution.

The universe is formed of the explosion of the primordial matter which forms the sun and then the earth. Various theories try to explain the origin of the universe out of which the most widely accepted theory was the “ Big Bang” theory. The earth is formed around 20 billion years ago which is in the form of the molten mass. The mass then cooled and forms the lighter elements and the molecules like water, ammonia, etc, which aggregates and form the protocell, and after development, the protocell is modified into the cell. Various theories try to explain the process of evolution out of which one is proposed by Lamarck but was not accepted because of its unreliability. Darwin also explains the theory of evolution after his observation and experience in the Galapagos island, in which he discovers
many species and their varieties.

The species on which Darwin proposed his theory was the species of finches which led him to propose the theory of evolution or the theory of natural selection.




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