Solution

According to Darwin, the organic evolution is due to interspecific competition. Interspecific competition is a form of competition in which individuals of different species compete for the same resource in an ecosystem (while intraspecific competition involved organisms of the same species). In interspecific competition, the individuals of different species having similar requirements like food, air, water and shelter etc. compete with each other.
Darwin proposed the model of interspecific competition as the motive force of organic evolution. This model derived its explanatory power from the fact that the different organisms were familiar with the industrial and social completion of which many characteristic features could be grasped and compared with biological phenomena without formal demonstration or proof.
Thus, the correct answer is the option (B), 'Interspecific competition'.