Evolution :
- Evolution is the gradual change occurring in living organisms over a long duration.
- This is a very slow-going process through which development of organisms is achieved.
- Formation of new species due to changes in specific characters of several generations of living organisms as a response to natural selection, is called as evolution.
- 3.5 billion years ago, life had been non existent on the Earth.
- At the beginning, there may have been only simple elements in the ocean on the Earth.
- Simple type of organic and inorganic compounds may have been formed from those.
- Complex compounds like proteins and nucleic acids may have formed over the long period from those simple compounds.
- First primitive type of cells may have been formed from the mixture of different types of organic and inorganic compounds.
- Number of those cells may have increased at the cost of surrounding chemicals.
- At present, crores of species of plants and animals with huge diversity regarding shape and complexity are present on the Earth.
- Different theories about 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, first living material (protoplasm) has been formed in ocean.
- In due course of time, unicellular organism was formed.
- Gradually, changes occurred in the unicellular organisms from which larger and more complex organisms were formed.
- All those changes were slow and gradual.
- Duration of all these changes is at most 300 crore years.
- Changes and development in living organisms had been all round and multi-dimensional and this led to evolution of different types of organisms. Hence, this overall process is called as evolution which is organizational.
- Progressive development of plants and animals from the ancestors having different structural and functional organization is called evolution.