The term Evooution was first coined by the British Philosopher, Herbert Spencer. According to Darwin Evolution is “The descent with modification”. In other words, Evolution is slow process in which the organisms react with the environment to accumulate gradual modification that lead to the formation of new species. As a result the simpler organisms give rise to more and more advanced new organisms. It actually involves continuous genetic variations. E.g. Evolution of horse from small simple Hyracotherium.