Isolation , genetic drift and natural variation are the main factor responsible for rise in new specie .

if an organism gets isolated from a specie due to some reason after many years it won't be able to breed with its ancestor specie

genetic drift is the change in the frequency of gene

and the characteristics or triads which help an organism to survive and reproduce are pass to the next generation and the characteristics which do not are not pass accumulation of this variation for a long period of time lead to the formation of new specie this is known as natural variation