Explain allopatric speciation with a geographic barrier and give a classic example.

Explain allopatric speciation with a geographic barrier and give a classic example.

• A. Speciation driven mainly by random mating where no barriers exist
• B. A gradual change in climate causing shared species to diversify evenly
• C. Geographic barrier prevents gene flow; populations diverge due to drift, selection, and mutation; example: squirrels separated by the Grand Canyon
• D. Speciation occurs when two populations mate at different times in the same area

Answer: (C)

Allopatric speciation happens when a geographic barrier physically splits a population, stopping gene flow between the two groups. Once isolated, each population evolves independently through genetic drift, natural selection, and new mutations. Over many generations, allele frequencies diverge, and distinct traits accumulate; eventually, the two groups become reproductively incompatible even if they meet again, completing the split into separate species. A classic illustration is squirrels on opposite sides of the Grand Canyon. The canyon acts as a barrier that prevents interbreeding between populations on different sides, allowing them to diverge under different environmental conditions and selective pressures. Other options describe scenarios without geographic separation or involve different isolation mechanisms (like mating being timed differently within the same area), which doesn’t capture allopatric speciation with a geographic barrier.

Allopatric speciation happens when a geographic barrier physically splits a population, stopping gene flow between the two groups. Once isolated, each population evolves independently through genetic drift, natural selection, and new mutations. Over many generations, allele frequencies diverge, and distinct traits accumulate; eventually, the two groups become reproductively incompatible even if they meet again, completing the split into separate species.

A classic illustration is squirrels on opposite sides of the Grand Canyon. The canyon acts as a barrier that prevents interbreeding between populations on different sides, allowing them to diverge under different environmental conditions and selective pressures.

Other options describe scenarios without geographic separation or involve different isolation mechanisms (like mating being timed differently within the same area), which doesn’t capture allopatric speciation with a geographic barrier.