When an ancestral population extends its range around a geographical barrier and differentiates (despite low-level gene flow), reproductive isolation occurs between terminal populations.

Social media, so often maligned, has done much to break down traditional geographical barriers and foster community connections and projects, from the very local to the truly global.

The selection knows no ideological or geographical barriers.

Speculates on the effect of rivers and other geographical barriers on the distribution of closely allied species. 1855:.

Geographical barriers such as the sea, mountains, or deserts serve as boundaries to the east and west.