Origin of life

Origin of life

Theory of special creation

This theory was proposed by Hebrew et. al and strongly supported by father Suarez. According to the bible, God created this universe, all animals, and plants including ocean, mountain etc. the life was created during 4004 BC in six consecutive days. The heaven and earth were created on the 1^st day. Sky was separated from water on the 2^nd day. On the 3^rd day, the land and plants were created. On the 4^th day, the sun, moon, and stars were created. On the 5^th day, fish and fowl were created. Animals were created on the 6^th day. The first human has Adam created from inanimate matter the clay which was furnished with soul. Then it started breathing. The first woman was Eve who was created from one of his ribs.

All existing animals and plants were created by god. According to Hindu mythology, Brahma (god of creation) created different forms of life. The body of all living beings was made up of five elements (Pancha maha Bhut) like the earth (Prithivi), water (Jala), fire (Akash), and air (Bayu). After the death, all these elements will be returned to Pancha maha Bhut.

This theory states that

1. The life was created by god or creator
2. Formed all of a sudden, out of nothing
3. No interrelationship among living beings and
4. Have not undergone any change

The life is a mysterious force or vital spirit that set living things completely apart from non-living and originated due to some supernatural event. It is accepted on the basis of faith. One should believe in the existence of god. However, this theory cannot be proved experimentally. So biologists do not believe in this theory.

Objections

Charles Darwin condemned special creation theory saying that earth has not always been inhabited by plants as we know now. It means there is always a change. This theory lacks sound logic, scientifically sound evidence. It could not convince scientists.

Theory of spontaneous generation or abiogenesis

Before the end of the seventeenth century, both biologists and philosophers believed that non-living things could arise from the non-living (inanimate) substance spontaneously. This remained true for centuries in the past. This theory was proposed by Von Helmont (1577-1644). In china, even from the earliest time, there was the belief that aphid and other insects under the influence of heat and moisture, come into existence. In sacred books in India, there is indication of the sudden emergence of different parasites, flies, beetles from sweat and manure. The Babylonian cuneiform text showed the worms and other creatures were formed from the mud of canals. In ancient Egypt, the conviction prevailed that layer of humus deposited by Nile river in its flood gave birth to living creatures like toads and frogs.

• Frogs, toads, snakes etc. were believed to be developed from mud
• Parasites, beetles flies etc. from sweat and manures
• Aphids and other insects arose under the influence of heat and moisture
• Fly maggots from fresh
• Young mice could arise from wheat grains and when these are kept in a dark room along with dirty clothes

Anaximenes (586-524 BC) proposed that air as the sole cause of life.

Aristotle (384-322 BC) proposed that worms, insects fish, tapeworm from excreta, crab, salamanders from earth can be developed.

Experiment of Von Helmet

Von Helmet kept the dirty shirt and few grains of wheat in a cupboard for 21 days. He observed mice developed from sweat and wheat. So, he proposed that both sexes of mice will be developed directly from non-living things. He conducted this experiment in the support of spontaneous generation.

We find the repetition of these tales in the writings of ancient Greeks like Thales (624-547 BC). Empedocles (485-425 BC), Democritus (460-370 BC), Plato (427-347 BC) and Aristotle (384-322 BC).

William Harvey (1578-1627) despite the statement that all life comes from the egg was not able to tear himself from the concept that lower forms of life may originate by spontaneous generation from non-living precursors.

Theory of biogenesis

This theory states that life is originated not from inanimate substance but from the preexisting forms only.

Redi’s classical experiment

Italian Physician Sir Francisco Redi (1621-1697) demonstrated that maggots were not created from meat or fishes. In his classical experiment, he placed lumps of boiled meat in jars, some uncovered, some covered with muslin cloth and some with parchment paper. After few days, he observed fly maggots only in the undiscovered jars.

The discovery of microbes by Van Leeuwenhoek (1632-1723) brought the question that microbes are so simple and could arise by spontaneous generation. This idea was authoritatively maintained by German philosopher Leibniz (1646-1716), French naturalist Buffon (1707-1788) and Englishman John Ne Dham (1713-1781).

The decline and fall of the theory of spontaneous generation

An Italian scholar Abbe Spallanzani tested the theory of spontaneous generation. In 1765, he prepared flasks of meat broth which were boiled for several hours and then sealed. This broth remained clear for months and when seals were broken and broth tested, it was shown to be free of microbes.

Spallanzani’s experiment was neither conclusive nor satisfying to many of his contemporary scientists. They claimed that by boiling, he had driven out the vital force needed for spontaneous generation. And also the sealed flask contained no oxygen.

The period of Louis Pasteur (1822-1895): Pasteur devised several experiments by which Spontaneous generation of microbes was discovered. The simplest and most sophisticated one was with the use of a swan-neck flask. He prepared meat broth in this flask and boiled for several hours. He then left the flask unsealed. The flask was not sealed and there was the free exchange of air with environment and system did not lack oxygen. Still, the swan-neck remained free of microbial contamination for months because their swan neck was so shaped to trap the viable microbial particles and allow only air to enter the flask. After several months, he broke the neck of the flask and did not find the microbes. This simple experiment thus altogether disproved the concept of spontaneous generation. Thus it was proved that life could arise only from the preexisting life which is known as Biogenesis.

Cosmozoic theory

This theory was proposed by Richer 1865 AD and supported by Arrhenius 1908 AD. It states that life came to this earth from another planet in the form of seed or spore or panspermia. So, spores finding the suitable environment grow into life. He could not explain a mechanism by which panspermia survived adverse condition of high in temperature and lethal radiation of interplanetary space during migration.

Catastrophic theory

It was proposed by G. Cuvier 1769-1832. This theory states that there have been several creations each preceded by a Catastrophy due to some major geological changes. Each Catastrophy destroyed previous life completely and was followed by next creation.

Steady state theory

This theory states that organisms have been unchangeable not only throughout existence but also they have existed and continue to exist unchanging till eternity. Hutton says there is no beginning and end. This theory was supported by Richter and Arrhenius etc.

References

Arvind, Keshari K. and Kamal K Adhikari. A Textbook of Biology. Vidyarthi Pustak Bhander.

Michael J.Pleczar JR, Chan E.C.S. and Noel R. Krieg. Microbiology. Tata Mc GrawHill, 1993.

Powar. and Daginawala. General Microbiology.

Rangaswami and Bagyaraj D.J. Agricultural Microbiology.