Geographic isolation leads to allopatric speciation
Explanation:
-One species could split into two if a physical barrier (such as a new river, divided its geographic range)
- If the barrier is large enough, gene flow between them would cease and the two separate populations would evolve independently.
- Different alleles would be fixed in them; because of the hazards of mutation and drift, or because selection favored different characters in the two.
- Then if the barrier is removed and the populations are reunited, they might remain distinct from each other.
- There would now be two species where there was formerly one.
