Mass extinctions lead to rapid speciation because they remove many species, leaving ecological niches and resources available to surviving populations. These survivors experience new selection pressures and may undergo adaptive radiation, producing multiple species over a relatively short geological period.
This is HL-only content in IB ESS subtopic 3.1, Biodiversity and evolution.
The Mechanism
A mass extinction is a geologically brief interval during which an unusually large proportion of Earth's species becomes extinct. Extinction does not directly create new species; instead, it changes environmental conditions and ecological relationships in ways that promote speciation.
| Stage | How it promotes speciation |
|---|---|
| Many species become extinct | Predators, competitors and parasites disappear, reducing existing biological pressures. |
| Ecological niches become vacant | Survivors gain access to newly available habitats, food sources and ecological roles. |
| Populations spread into different environments | Geographical or ecological separation reduces gene flow between populations. |
| Different selection pressures act | Natural selection favours different adaptations in each environment. |
| Reproductive isolation develops | Accumulated genetic, behavioural or ecological differences prevent interbreeding, producing new species. |
After the Cretaceous to Paleogene mass extinction approximately 66 million years ago, non-avian dinosaurs disappeared. Mammals survived and diversified into many vacant terrestrial niches, eventually producing groups adapted for running, swimming, flying and climbing.
“Rapid” is relative: speciation may still take thousands or millions of years, but this is fast on a geological timescale. A common misconception is that biodiversity immediately returns to its previous level. Recovery takes time, and the new ecosystems contain different species and interactions.