The origin of life is a fascinating and perhaps an unique event in the history of universe. How did life originate on the earth? In order to explain it a number of views have been expressed from time to time. Most of these views are quite bizarre with only a historical significance. Here we shall discuss about some important theories about the origin of life.
SPECIAL CREATION THEORY
According to the special creation theory, life originated on the earth due to supernatural event. All plants and animals appeared on the earth in the form they exist today. A supernatural power— may be the God, created all living beings on the earth. This theory is upheld by most of world's major religions and civilizations and based purely on faith. Since the process of special creation occurred, it cannot be observed. This is sufficient to put the concept of special creation outside the framework of scientific investigation. Science concerns itself only with observable phenomena and as such will never be able to prove or disprove special creation.
THEORY OF SPONTANEOUS GENERATION
This theory was prevalent in ancient Chinese, Babylonian and Egyptian civilizations as an alternative to the theory of special creation, with which it coexisted. According to this theory, life has originated from non-living organic matter abiogenetically, i.e. without the intervention of living things.
BIOGENESIS THEORY
In 1861, Louis Pasteur (1822-1895) had disproven the concept of spontaneous generation to find out the origin of life. He took a flask and half filled it with sugar and structure (swan-necked flask). The contents of the flask
Pasteur's Experiments
were boiled till steam passed out from the tube and then they were cooled. He did not find any change in the contents even after several days. There was no growth of organisms. This was due to the fact that when the air entered the flask, all air-borne particles got stuck at the bend of the tube and only pure air reached the syrup which remained sterile. After he broke the neck of the flask there was direct contact of the contents with the air and a thick growth of micro-organisms appeared in the flask.. This simple experiment conclusively disproved the idea of spontaneous generation.
In 1767, Abbe Lazzaro Spallanzani (1729-1799) prepared a nutritive broth of vegetables and meat and placed it in flasks and sealed their necks so that air could not enter inside. He then boiled the broth for four hours and left it in the flasks for several days. He observed that no organisms appeared in the flasks and, therefore, concluded that microorganisms are not formed spontaneously, but from those already present in the air. In 1748, John T. Needham criticized Spallanzani's experiment, maintaining that overheating of the broth rendered it unfit for spontaneous generation. Infuriated by this statement, Spallanzani broke the neck of his sealed flask and as air got into it the broth boomed with rich bacterial growth within a few days. In 1861, Louis Pasteur (1822-1895) finally refuted the concept of spontaneous generation. He took a flask and half filled it with sugar and structure (swan-necked flask). The contents of the flask were boiled till steam passed out from the tube and then they were cooled. He did not find any change in the contents even after several days. There was no growth of organisms. This was due to the fact that when the air entered the flask, all air-borne particles got stuck at the bend of the tube and only pure air reached the syrup which remained sterile. After he broke the neck of the flask there was direct contact of the contents with the air and a thick growth of micro-organisms appeared in the flask. This simple experiment conclusively disproved the idea of spontaneous generation as the origin of life. So it is now clear that a living organism was required in order to produce another living organism. And so the Biogenes is the theory failed to find out any concept about the origin of life.
STEADY-STATE THEORY
This theory asserts that the earth had no origin, has always been able to support life, has changed remarkably little, if at all, and that species had no origin. The theory does not accept the palaeontological evidence that presence or absence of a fossil indicates the origin or extinction of the species represented.
COSMOZOAN THEORY
This theory does not offer a mechanism to account for the origin of life but favors the idea that it had an interplanetary origin. It does not therefore constitute a theory of origin of life as such, but merely transposes the problem to elsewhere in the universe. This theory claims that life is as eternal as matter itself. These theories of inter-planetary exchange of viable spores became obsolete in the light of subsequent researches. Next we shall discuss about the Biochemical Origin of Life. Click Here Click For