What is meant by Evolution? Theory of Evolution ?

What is Evolution? 

Evolution is the gradual change occurring in living organisms over a long duration. This is a very slow-going process through which the development of organisms is achieved. 

All the stages in changes in various components ranging from stars and planets in space to the biosphere present on the Earth should be included in the study of evolution. The formation of new species due to changes in specific characters of several generations of living organisms due to natural selection is called evolution. 

3.5 billion years ago, life had been nonexistent on Earth. In the beginning, there may have been only simple elements in the ocean on the Earth, and simple types of organic and inorganic compounds may have been formed from those. Complex compounds like proteins and nucleic acids may have formed over a long period from those simple compounds. 

The first primitive type of cells may have been formed from the mixture of different types of organic and inorganic compounds. A number of those cells may have increased at the cost of surrounding chemicals.

There may have been some differences among those cells, and according to the principle of natural selection, some may have shown good growth, and some may have perished which could not adjust with the surrounding. 

At present, crores of plants and animals with huge diversity regarding shape and complexity are present on the Earth. s The plant diversity consists of various species ranging from unicellular Chlorella to the huge banyan tree Animals' diversity ranges from the unicellular Amoeba and Paramecium to man and giant whales. 

Life exists on Earth everywhere, from the equator to both the poles. Organisms are present in all the places like air, water, land, rock, etc. Humans have shown curiosity about the origin of life and the reasons for such a great diversity in life present on the Earth since the ancient period. 

Different theories about the origin and evolution of life have been proposed till today, of which theory of Gradual development of living organisms is accepted. 

Theory of Evolution? 

According to this theory, the first living material (protoplasm) has been formed in the ocean. In due course of time unicellular organism was formed. Gradually changes occurred in the unicellular organism from which larger and more complex organisms were formed. 

All those changes were slow and gradual. The duration of all these changes is at most 300 crore years. Changes and development in living organisms had been all round and multiple-dimensional, and this led to the evolution of different types of organisms. 

Hence this overall process is called organizational evolution. The progressive development of plants and animals from the ancestors having different structural and functional organizations is called evolution. 

Evidence of Evolution? 

Collective thinking, upon all the above-mentioned theories, implies that evolution is the everlasting process of changes. However, it needs proof to prove it. Following are various proofs available in support of the theories mentioned above. 

1. Morphological Evidence.

2. Anatomical Evidence. 

3. Vestigial Organs. 

4. Palaeontological Evidence. 

5. Connecting Links. 

6. Embryological Evidence. 

Embryological Evidence. 

Comparative study of embryonic development stages of various vertebrates given in the picture shows that all embryos show extreme similarities during the initial stages and those similarities decrease gradually. Similarities in the initial stages indicate the common origin of all these animals.