Allopatric speciation is primarily caused by which factor?

Allopatric speciation occurs when populations of a species are geographically isolated from each other, leading to the development of distinct species over time. The primary factor that drives this process is geographical barriers, such as mountains, rivers, or distance, which prevent individuals from interbreeding. When populations are separated, they can evolve independently in response to different environmental pressures, adapt to their unique habitats, and accumulate genetic differences.

These changes can be influenced by natural selection, genetic drift, and other mechanisms that operate differently in isolated populations as they adapt to new ecological niches or face different selective pressures. Over time, these accumulated differences can lead to reproductive isolation, ultimately resulting in the emergence of new species. Thus, geographical barriers are the essential catalyst for allopatric speciation, facilitating the divergence of populations into separate evolutionary lineages.