Evolution is descent with modification or continuity of life with constant modifications. It means the living being modify and adopt according to the ever-changing environmental needs.
These modifications in the organisms keep accumulating generation after generations, resulting in more complex and better adapted new species. The evolution is taking place owing to the following reasons:
1. The environmental conditions are ever changing.
2. Life is capable of changing with changing environmental conditions. This is called adaptability. The organization of living beings changes in order to adapt to changed environmental conditions. This leads to the evolution of new forms and new species.
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3. Evolution is a continuous process. Individuals had changed, have been changing and will continue to change.
4. All present species had common ancestors at some time of their evolution. This is called monophyletic genealogy.
5. Individuals migrate from their place of origin to varied geographical areas and gradually adapt to different sets of environmental conditions. These results in the formation of several new species form one ancestral species.
6. Evolution is very complex and extremely slow process. It is not possible to see one type to animals changing to other, but presence of intergrading organisms supports the concept of evolution.