Which process involves isolation by a geographic barrier leading to speciation?

• A. Speciation
• B. Allopatric Speciation
• C. Habitat
• D. Niche

Answer: (B)

Isolating populations with a geographic barrier stops gene flow between them. When two groups are cut off by mountains, rivers, or distance, they begin to diverge genetically because mutation, genetic drift, and natural selection act independently in each place. Over many generations, these differences can become strong enough that individuals from the two groups no longer interbreed successfully, even if the barrier is removed. This sequence of events is a classic path to forming new species and is specifically described as allopatric speciation.

Other terms like speciation in general refer to the process of forming new species, but don’t specify the geographic mechanism. Habitat and niche describe where a species lives and how it interacts with its environment, not the process by which new species arise.