05 Origin and Evolution of life - part 04 - Organic Evolution

05 Origin and Evolution of life - part 04 - Organic Evolution


Organic Evolution : 
  • Evolution (Latin word, e = from; volvere = to roll) means the act of unrolling or unfolding of nature. 
  • It brings about orderly changes from one form to another. 
  • These changes result in descendants becoming different from the ancestors. 
  • Organic evolution can be defined as slow, gradual, continuous and irreversible changes through which the present day complex forms of the life developed (or evolved) from their simple pre-existing forms. 
  • According to Charles Darwin, evolution is `descent with modification'.  
  • According to this theory, the traits are acquired due to internal force, changes in environment, new needs and the use and disuse of organs. 
  • After several generations, it gives rise to new species. 
  • This theory was disproved by a German biologist August Weismann, who cut the tails of many rats for several generations but could not find any change in size of tail even after 21generations. 
  • He concluded that variations produced in somatic cells (somatoplasm) are not inheritedwhile variations produced in germ cells (germplasm) are inherited to next generationand he proposed the theory of Germplasm.

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