Summary
Suggests species remain stable for long periods interrupted by short bursts of rapid change.
In depth
Eldredge and Gould (1972) proposed that fossils often show long stability and rapid change coinciding with speciation, rather than gradual change. Some lineages show both patterns.
It is compatible with Darwinian selection, which can operate quickly on geological timescales.
The theory arose from the observation that fossil lineages often show stasis, with changes appearing abruptly at speciation events, a pattern in which rapid means thousands of years, which is quick in geological time. It does not imply sudden saltations; speciation in small isolated populations can lead to quick change, which is hard to preserve in fossils.
Stasis can be explained by stabilising selection, developmental constraint or habitat tracking. Examples come from Bryozoa, trilobites and Lake Turkana molluscs, while others, such as planktonic foraminifera, show gradual change, so both modes occur. Some lineages show bursts after environmental change.
Frequently asked questions
What is Punctuated Equilibrium?
Suggests species remain stable for long periods interrupted by short bursts of rapid change.
Which area of biology covers Punctuated Equilibrium, and how advanced is it?
Punctuated Equilibrium is one of the 53 topics in Evolution. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Cambrian Explosion, Evolution, Macroevolution.
Why does Punctuated Equilibrium matter?
The debate refined how palaeontologists view the tempo of evolution, and it is not in conflict with Darwinian selection.
Can you give an example of Punctuated Equilibrium?
Certain trilobites and bryozoans show stasis with abrupt changes.
What should I learn before Punctuated Equilibrium?
Work through the Beginner topics in Evolution first, such as Evolution, Natural Selection, Charles Darwin, then return to Punctuated Equilibrium. Advanced topics assume the Intermediate vocabulary.
What topics are related to Punctuated Equilibrium?
The closest topics to Punctuated Equilibrium are Cambrian Explosion, Evolution, Macroevolution, Ancient DNA. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Punctuated Equilibrium?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Punctuated Equilibrium. To practise the whole of Evolution, use the Evolution quiz.
How is Punctuated Equilibrium different from Cambrian Explosion?
Punctuated Equilibrium: Suggests species remain stable for long periods interrupted by short bursts of rapid change. Cambrian Explosion: A rapid diversification of animal body plans about 540 million years ago. Read both side by side and note what each one explains.
How should I study Punctuated Equilibrium step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Cambrian Explosion and explain the difference aloud. Finally, take the Evolution quiz and come back to this page for any question you miss.