Biology · Chapter 10
Study notes aligned to the official NEB syllabus.
Evolution is a slow and progressive change resulting in complexity from simple and lower organisms, taking place over millions of years on earth. This chapter reviews the classical theories about how life originated and the modern biochemical account of the origin of life.
Proposed by some spiritual people. According to this view, all the existing plants and animals were created by some supernatural power or God. The first man was Adam and the first woman Eve. According to Hindu mythology, God Brahma created various forms of life as such in one stroke; the first man was Manu and the first woman Shraddha. As the theory has no scientific evidence, it is not accepted at present. However, it was accepted by a Spanish priest, Father Saurez.
Proposed by the philosopher Ritcher and supported by Arrhenius. According to this theory, life came to the earth from another planet in the form of small spores called panspermia. When the planet collided with the earth, the panspermia came to the earth and developed into different forms of life. As this theory has no scientific proof, it is not accepted.
In the early 19th century, both scientists and philosophers believed that living things could arise from inanimate substances. For example, frogs, toads and snakes were believed to be created from mud, and parasites, beetles and flies were believed to arise from sweat and manure. As this theory has no scientific evidence, it is not accepted.
This theory states that life originated not from non-living substances but from living organisms which were already present in the atmosphere in pre-existing forms. When they get a suitable condition or medium, they grow and multiply. Many scientists established the theory of biogenesis with experiments, as follows.
i. Redi's experiment: Redi made an experiment using two jars. He kept lumps of boiled meat in both jars. One jar was left uncovered and another was covered (with gauze or muslin cloth, and others with parchment paper). The experiment was left for a few weeks.
ii. Spallanzani's experiment: he set up two sets of experiments using flasks. He poured hay infusion in all flasks. They were boiled to sterilize them. The experiment was left for a few days.
iii. Pasteur's experiment: he used a swan-necked flask. He kept hay infusion in the flask and sterilized it by boiling. The mouth of the flask was closed. He left the experiment for 18 months.