Selection Charles Darwin explained the theory of evolution in his book ‘The Origin of Species by Natural Selection’. During his journey around the Earth, he made extensive observations of plants and animals. He noted a huge variety and remarkable similarities among organisms and their adaptive features to cope up to their environment. He proved that fittest organisms can survive and leave more progenies than the unfit ones through natural selection.
Darwin’s theory was based on several facts, observations and influences. They are: . Over production (or) prodigality of production All living organisms increase their population in larger number. For example, Salmon fish produces about million eggs during breeding season and if all of them hatch, the seas would be filled with salmon in few generations.
Elephant, the slowest breeder that can produce six young ones in its life time can produce million descendants at the end of years in the absence of any check. . Struggle for existence Organisms struggle for food, space and mate. As these become a limiting factor, competition exists among the members of the population.
Darwin denoted struggle for existence in three ways – Intra specific struggle between the same species for food, space and mate. Inter specific struggle with different species for food and space. Struggle with the environment to cope with the climatic variations, flood, earthquakes, drought, etc., . Universal occurrence of variations No two individuals are alike.
There are variations even in identical twins. Even the children born of the same parents differ in colour, height, behavior, etc., The useful variations found in an organism help them to overcome struggle and such variations are passed on to the next generation. . Origin of species by Natural Selection According to Darwin, nature is the most powerful selective force.
He compared origin of species by natural selection to a small isolated group. Darwin believed that the struggle for existence resulted in the survival of the fittest. Such organisms become better adapted to the changed environment.