Darwin's theory of natural selection
Charles Robert Darwin (1809-1882), a naturalist, biologist, geologist and son of a wealthy doctor of England, proposed the idea of natural selection. He took a voyage to South America and the islands off its coast. During this voyage, He collected a lot of information about all forms of life. The studies he conducted during this expedition were to change forever the way we look at the variety of life on earth.
Darwin considered variations, struggle for existence and heredity as the chief factors of evolution. Due to struggle for existence and heritable variations, only those individuals survive which are best suited to new conditions of life. Such selection is known as natural selection or survival of the fittest. Natural selection shows the automatic weeding out of the less perfect forms.
Darwin illustrated the survival of the fittest by natural selection with the example of giraffe. In a population of giraffes those with somewhat short neck lengths could not reach the leaves on tall trees. They did not get enough food to survive and to reproduce. On the other hand, giraffes with longer neck got enough food and produced more offspring. Thus, giraffes with longer necks and legs became abundant and the other ones with the shorter necks and legs gradually got eliminated.
By the passage of time, the best suited individuals survived and became adjusted to the nature. With the change in the environment, new adaptations appear in organisms. The later descendants after several generations become quite distinct for their ancestors. In this way new species appear.