Which of the following best characterizes allopatric speciation?

Allopatric speciation is primarily defined by the geographical separation of populations, which leads to reproductive isolation and ultimately the formation of distinct species. This process occurs when a population is divided by a physical barrier, such as a mountain range, a body of water, or a vast distance. Over time, the isolated populations experience different selective pressures, mutations, and genetic drift, which can lead to the development of unique adaptations and reproductive barriers. As these populations diverge genetically, they become increasingly different from one another, eventually resulting in the emergence of distinct species. This geographical isolation is the key factor that drives the speciation process in allopatric scenarios, allowing for evolutionary changes to accumulate independent of one another.