Darwin in his "Natural Selection Theory" did not believe in any...

The theory of natural selection is based on the following factors : (i) Rapid multiplication and limited food and space which leads to struggle for existence. (ii) Struggle for existence and variations which leads to natural selection or survival of the fittest. (iii) Natural selection and inheritance of useful variation over many generation which leads to formation of new species. Darwin in his 'Natural Selection Theory did not believe in the role of discontinuous variation in natural selection. Darwin always believed in the universal occurrence of variation. In his opinion, variation is continuous in nature. Related Theory Because resources are limited in nature, organisms with heritable traits that favour survival and reproduction will tend to leave more offspring than their peers, causing the traits to increase in frequency over generations.