Final answer:
Geographic isolation of populations most likely leads to allopatric speciation. Longer distances between divided groups increase the rate of allopatric speciation as they enhance reproductive isolation and prevent gene flow.
Step-by-step explanation:
The situation that would most likely lead to allopatric speciation is (c) Geographic isolation of populations. Allopatric speciation occurs when biological populations of the same species become isolated from each other to an extent that prevents or interferes with genetic interchange. This can happen through various means such as the formation of a new river, erosion creating a new valley, or organisms traveling to an isolated location, like seeds drifting to an island. Geographic barriers like these lead to reproductive isolation, after which the separated populations can diverge genetically over generations due to mutation, genetic drift, and natural selection.
Concerning the variable that increases the likelihood of allopatric speciation taking place more quickly, the correct answer is (b) longer distance between divided groups. Greater distance can enhance reproductive isolation, preventing gene flow and thereby allowing genetic divergence to occur at a faster rate.