7.10 Speciation

Making new species

Speciation is the formation of new species. Under the biological species concept, a species is a group that can interbreed and produce fertile offspring. New species form when populations become reproductively isolated — barriers (prezygotic or postzygotic) prevent them from interbreeding.

Two routes

Allopatric speciation happens when a geographic barrier (a river, mountain) separates populations, which then diverge. Sympatric speciation happens without geographic separation — populations diverge while living in the same area (e.g., through polyploidy in plants).

Key terms

Speciation

The formation of new species from existing ones.

Reproductive isolation

Barriers that prevent populations from interbreeding — required for speciation.

Allopatric speciation

New species form after a geographic barrier separates populations.

Sympatric speciation

New species form without geographic separation (same area).

Biological species concept

A species is a group that can interbreed and produce fertile offspring.

Try an AP-style question

Two populations of squirrels on opposite sides of the Grand Canyon can no longer interbreed. What kind of speciation most likely occurred?

1. Speciation caused by gene flow between them
2. Allopatric speciation caused by geographic isolation
3. Sympatric speciation within one shared habitat
4. Polyploidy in one of the populations