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Why do geographic barriers cause populations to become different over time?
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biogeographic region
Floral kingdoms, subkingdoms, and major regions of the world.
Geographic barriers, such as mountain ranges, rivers, or deserts, cause populations to become different over time primarily by interrupting gene flow between them. When a physical barrier separates a single population into two or more groups, they no longer share a common gene pool, preventing them from interbreeding.123
Once isolated, these populations diverge through several mechanisms:
- Adaptation: Each group faces unique environmental conditions and selection pressures. As they adapt to their specific surroundings, their genetic compositions change, often leading to phenotypic differentiation.12
- Genetic Drift: In smaller, isolated populations, genetic drift—the random fluctuation of gene frequencies—can cause significant changes over generations, potentially leading to the loss of certain alleles.45
- Reproductive Isolation: Over time, these accumulated genetic differences may become so substantial that the populations can no longer interbreed, even if the geographic barrier were removed. This process, known as allopatric speciation, is a primary driver of biological diversity.12
Ultimately, these barriers act as a wedge that allows related groups to evolve independently, eventually resulting in distinct subspecies, species, or even higher taxonomic groups.3