(i) Evolution is a gradual change occuring in living organisms over a long duration.
(ii) This is a very slow- going process through which development of organisms is achieved.
(iii) All the stages in changes occurred 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.
(iv) 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.
(v) Different theories about origin and evolution of life have been proposed till today of which theory of gradual development of living organisms is accepted.
(vi) According to this theory, first living material (Protoplasm) has been formed in the ocean. In due course of time, unicellular organism was formed.
(vii) Gradual changes took place in unicellular organism from which larger and more complex organisms were formed. Duration of all these changes is about 300 crore years.
(viii) Changes and development in living organisms has 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.
(ix) Progressive development of plants and animals from the ancestors having different structural and functional organization is called evolution.
