Man is a product of evolution. Therefore human evolution is intimately related to the origin of life and its development on the face of earth. It is customary to speak of evolution ‘from amoeba to Man’, as if the amoeba is the simplest form of life. But in reality, there are several organisms more primitives than amoeba, say for example viruses. The evolution from a self-replicating organic molecule to a protozoan, like amoeba, is the most complex step in evolution, which might have consumed the same extent of time from protozoan to man.
The term evolution was first applied by the English philosopher Herbert Spencer to mean the historical development of life. Since then evolution denotes a change, although the term may be defined in several ways. In the context of man, the biological evolution started with the ‘Origin of life’. In the beginning, there was nothing. The first successful formation of protoplasm initiated the life and its continuous development proceeded towards complexity to give rise different life forms of evolved type.
About 10 billion years after the formation of Universe, the earth was formed. Life on earth appeared far late, nearly three billion years ago. Of the several evolutionary problems, perhaps the origin of life is the most critical, since there is no record concerning it. Life has been characterized by the capacity of performing certain vital functional activities like metabolism, growth and reproduction. There is no ambiguity regarding this point. But how the first life came on earth is a matter of conjecture.
Ancient thinkers speculated that life originated spontaneously from inorganic components of the environment, just after the formation of earth. A series of physio-chemical processes were perhaps responsible behind this creation. Aristotle (384 BC to 322 BC) was the pioneer in this line of thought and nobody raised any voice against his speculation till seventeenth Century. But in seventeenth Century, an Italian scientist, Francesco Redi (1627 -1697) made an experiment with two pieces of meat.
One of the pieces was kept fully covered and the other piece was kept in an open place. After some days he examined both of the pieces very carefully. He noticed that, flies laid eggs on the uncovered piece of meat and so many new flies had born. But the covered piece of meat had not produced any new fly, as there was absolutely no access of flies
Redi tried to establish the fact, that living organisms cannot be originated spontaneously from inorganic components. More or less at the same time, Leuwenhock (1632 – 1723) by studying several microorganisms like protozoa, sperm, bacteria etc. under microscope declared that the spontaneous generation was possible for the microorganisms. Later, Louis Pasteur (1822 -1895) also studied much to furnish evidences in support of spontaneous creation.
In fact, scientists of this period were perplexed in finding out how life began spontaneously as a matter of chance. Philosophers, Thinkers and Scientists all had submitted their varied thought and propositions regarding the nature and mechanism of origin of life on earth. Different religions had also put forth different concepts in this connection.