When Scientists, farmers and/or breeders allow only individuals with certain characteristics (desirable characteristics for a given purpose, i.e.: bigger fruits in some plants), this will result in the formation of new species by a process called Artificial Selection; because people, instead of nature, selects wich pairs of individuals will reproduce.
There is a large number of examples of this speciation process that we can point out: dogs are the result of the process of selecting only the most docile and manageable wolves of the breed.