Which type of speciation occurs when a physical barrier splits one population into separate evolutionary groups?

Allopatric speciation occurs when a physical barrier splits one population into separate evolutionary groups.

The barrier may be a mountain range, river, canyon, glacier, or stretch of unsuitable habitat. Once separated, the populations experience different mutations, natural selection pressures, and random genetic changes. Reduced gene flow allows differences to accumulate, and reproductive isolation may eventually evolve.

The word allopatric comes from Greek roots meaning “different homeland.” Geographic separation itself does not instantly create new species; the separated populations must diverge sufficiently that they no longer exchange genes successfully when contact is restored.

Island populations are frequent examples because colonists can become isolated from mainland relatives. Allopatric speciation contrasts with sympatric speciation, in which reproductive isolation evolves without a geographic barrier, often through ecological specialization, chromosome changes, or strong mate preferences.