Charles Darwin is the father of evolution. He believed that evolution is a gradual process and new species evolve by natural selection.
Natural selection is a process in which heritable variations enabling better survival are enabled to reproduce and leave a greater number of offspring.
But Darwin’s theory had some shortcomings which were addressed by certain scientists like Dobzhansky, Fisher, Mayr, Stebbins, Haldane and Wright. They proposed the modern synthetic theory of evolution.
The modern synthetic theory of evolution or Neo-Darwinism, is an improvement of Darwin’s theory of natural selection. It is a combination of ideas from Darwin's theory of natural selection, mutation theory and Mendel’s principles of heredity.