Question

Why does gene flow prevent speciation?

Answer 1

It causes the introduction of new genes to the existing gene pool creating a variation, so that the best one is selected by the nature.

Answer 2

Answer:

Gene flow prevents  reproductive isolation of populations and prevents speciation.

Explanation:

Speciation is the process of formation of new species from the existing ones. Two species are reproductively isolated and cannot interbred to produce fertile progeny. Gene flow is exchange of alleles between local populations and does not allow them to become reproductively isolated. Since the two populations can interbreed, they cannot form two separate species.