Until seventeenth century people believed in abiogenesis or spontaneous generation of living organisms from nonliving substances. According to Epicurus (342 � 271 B.C.), an ancient Greece, worms and numerous other animals were generated from the soil or manure by the action of moisture and warmth of the sun and air. According to Aristotle (384-322 B.C.) living creatures are born from like species no doubt, but they also arise spontaneously. Thus, common worms, beer larvae, wasps, ticks, glow worms and various other insects are born from dew, rotten slime, manure, dry wood, sweat and meat etc. Even two thousand years later, van Helmot described that mice arise from wheat barn and sweaty shirt kept in a pot for 21 days in dark. Similarly, a variety of bird the barnacle goose was presumed to be derived from some barnacle living in sea, or from goose tree.
Theory of Biogenesis
1. Redi�s exoeriment- By conducting simple experiments, Italian physician Fransciso Redi demonstrated that abiogenesis cannot exist. He cooked few meat pieces and placed them in three jars. Jar 1 was left uncovered, Jar2 was covered with fine muslin cloth and Jar3 was covered with parchment paper. In few days maggots appeared in Jar 1 but not in 2 and 3. Plenty of flies were seen sitting and laying their eggs on the muslin cloth covering jar2 but no maggots appeared on the meat. From these observations Redi concluded that the flies arise from the eggs laid down by the parent floes and that maggots cannot appear spontaneously.
2. Pasteur�s Experiment- He kept a mixture of sugar and yeast powder in a flask and filled about half of it with water. He then softened the neck and made it into S shaped. The contents of the flask were boiled till strong current of stream rushed out from the side tube. After this the flask was cooled. It was noted that the contents of the flask remain unchanged even after many days. But when the neck of the flask cut off, the solution soon of the flask soon showed thick growth of organisms. This could be explained by presuming that air contains microorganism which in first case could not reach the content of the flask.
Modern Hypothesis of Origin of Life
The modern hypothesis of origin of life was formulated by Haeckel, who considered that the most primitive organisms would have generated spontaneously at some time from some inorganic matter as a result of formative action of some special external forces as electric charges, ultraviolet light and corpuscular radiations of radioactive elements. The genius work of Haldane, A.I. Oparin, Stanely Miller, H. Urey and others provided evidences in favour of this hypothesis.
Oparin suggested that from the simple compounds like carbon, hydrogen, oxygen, nitrogen, more and more complex organic compounds were formed gradually under the influence of electric discharge or corpuscular radiations.
The synthesis of carbohydrates, fats and amino acids and other complex organic suctances probably occurred in sea, which had been described by Haldane as �the hot dilute soup�.
