Complete information on the 6 theories of non chemical origin of life

Complete information on the 6 theories of non chemical origin of life

There have been several theories concerning the origin of life. These may be regarded as religious, semireligious and scientific. The following are some of the theories.

1. Theory of special creation.

2. Theory of spontaneous generation (Abiogenesis theory)

3. Theory of Eternity of life.

4. Theory of Panspermia or cosmozoic theory.

5. Theory of Vital forces

6. Theory of Chemical evolution.

1. Theory of special creation:

According to this theory, all the life forms have been created specially and particularly by some supernatural force. Many religions of the world hold this opinion. The Christian theory of the origin of life as explained in the Bible believes that God created different forms of life in the beginning and as the final act of creation man came into existence. As this theory is purely based on faith no evidence is available.

2. Theory of spontaneous generation:

This theory is also known as the Abiogenesis theory, meaning life coming from a non living source. Ac­cording to this theory, life is being continuously generated from non living sources. Many of the early European scientists notably – Anaximander, Anaxagoras, Needham and others believed that the small forms of life are continuously generated from the non living material.

In the 18th century, people believed that maggots, flies and worms suddenly arise from decay­ing vegetable matter. They also believed that frogs come to the earth through rain water. Even the great Aristotle believed in the theory of Abiogenetic origin of life.

It is true that some time in the remote past life should have come from a non living source. That must have occurred only once. Since then life is not being generated from a non living source. But it has maintained itself through millions of years because of its capacity of reproduction. Many European scientists notably Fransesco Rheedi, Lazzaro Spallan zani and Louis Pasteur have clearly proved through their experimental evi­dences that the theory of spontaneous generation is not correct.

Franscesco Rheedi was perhaps the first person to provide experimental evidence against the theory of spontaneous generation. He showed that the white maggots that appear in the meat were the larvae of flies and nothing else. He showed this by setting up an experiment whereby the meat was protected by a muslin cloth.

When the meat was not exposed to air, worms did not appear in the meat. He therefore concluded that the decaying meat was not generating the maggots but it only offered a suit­able environment for the laying of the eggs by the flies and their subse­quent development into flies.

Lazzaro Spallanzani an Italian priest and scien­tist disproved the theory of spontaneous genera­tion in the year 1765. He took a piece of meat kept it in a long necked flask, boiled it and then sealed the flask. Even after sev­eral months the broth re­mained clear and there was no development of maggots or worms. John Needham who was a supporter of Abiogenesis theory argued that by boiling the broth the vital force necessary for the origin of life was de­stroyed. That is why worms did not develop in the sealed broth.

Spallanzani could not satisfactorily answer this criticism. It was left to the great microbiologist Louis Pasteur (1822 – 1895) to give conclusive evidence against the theory of spontaneous generation. For his experiments he used a goose necked or swan necked flask. He boiled a solution of sugar and yeast for several hours.

Then the flask was left unsealed for the free ex­change of air with the outside environment. Even after several weeks there was no development of microbes in it. Because the neck of the flask was shaped in such a way as to trap the outside dust particles or microbes in the neck allowing only the air to reach the solution.

In this way the solution inside the flask remained germ free. By breaking the neck of the flask Pasteur reported the development of microbes once again. The experiment of Louis Pastuer clearly showed that life can arise only from a preexisting life and the abiogenetic theory of life is not correct. This means that the present life forms can only come from preexisting life. This is called the biogenetic theory.

Theory of Eternity of life:

This theory believes that life has been in existence indefinitely. Hence the question of origin of life does not arise. Theory of Panspermia or Cosmozoic theory: According to this theory, life did not originate on earth. It must have originated in another part of the universe from where it has been transferred to earth in the form of resistant spores or seeds called cosmozoans.

These cosmozoans during their space travel have reached the earth accidentally and have evolved on this planet. To date there is no tangible evidence for this theory. Theory of vital forces: This theory is some what similar to the theory of special creation.

According to this theory the living beings and all the chemical compounds present in them require a vital force and they also believed that this vital force is responsible for all the unique properties of living beings. They argued that the compounds present in living beings – organic compounds are present only in the living beings and are not present outside of the body of living organisms.

Many attempts by chemists to synthesise organic compounds in the laboratory had failed. And this seemed to support the vital force theory. The supporters of vital theory argued that chemicals of living beings have a vital force, and can be created only by a supernatural force, and man being a product of this force can neither control nor is in a position to repeat this.

In the year 1828, Frederick Wohler for the first time synthesised urea (chemical compound present in the urine of animals) in the laboratory using inorganic compounds. This was a great blow to the supporters vital force theory, as they believed no organic compound can exist much less be synthesised outside the body of living organisms. Since then a number of organic compounds have been synthesised in the laboratory and today synthesis of organic compounds is a very normal affair in the chemistry laboratory.