Question

How do new species separate from existing species?

Answer 1

Typically a species is defined by a group of organisms capable of breeding with each other and being able to have children, who in turn are capable of breeding. The second half of the sentence accounts for hybrid crossings (such as donkey+horse), which are capable of producing STERILE offspring

Answer 2

New species are made by an isolated group of organisms evolve so much they can't interbreed. Species can either be isolated geographically by a natural disaster (e.g a landmass splits apart) or by a difference in mating times (e.g one group mates in the spring, the other in the fall). Sorry I left this part out of the first response