How can environmental barriers contribute to speciation?

Environmental barriers contribute to speciation primarily by separating populations and reducing gene flow. When populations of the same species become geographically isolated due to environmental factors such as mountains, rivers, or climate changes, they can no longer interbreed. This isolation means that the genetic exchange that normally occurs through mating is halted, leading to divergent evolutionary paths.

As these separated populations adapt to their unique environments, different selective pressures will drive changes in their genetic makeup. Over time, accumulated genetic differences can result in populations that are no longer capable of interbreeding, even if they come back into contact. This process ultimately leads to the emergence of new species, a concept known as allopatric speciation.

In contrast, options that suggest enhancement of gene flow, encouragement of hybridization, or maintenance of genetic similarity do not lead to speciation. Instead, these factors typically promote gene continuity and homogenization within populations, rather than the divergence required for speciation to occur.