Image Caption
This process would produce the following pattern in the fossil record: Evolution appears to happen in sharp jumps associated with speciation events.
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Punctuated equilibrium (1 of 8) Stasis
Stasis: A population of mollusks is experiencing stasis, living, dying, and getting fossilized every few hundred thousand years. Little observable evolution seems to be occurring judging from these fossils.![](https://evolution.berkeley.edu/wp-content/uploads/2021/10/45469_evo_resources_resource_image_236_original-350x200.gif)
Punctuated equilibrium (2 of 8) Isolation
Isolation: A drop in sea level forms a lake and isolates a small number of mollusks from the rest of the population.![](https://evolution.berkeley.edu/wp-content/uploads/2021/10/98058_evo_resources_resource_image_237_original-350x139.gif)
Punctuated equilibrium (3 of 8) Strong selection and rapid change
Strong selection and rapid change: The small, isolated population experiences strong selection and rapid change because of the novel environment and small population size: The environment in the newly formed…![](https://evolution.berkeley.edu/wp-content/uploads/2021/10/36812_evo_resources_resource_image_238_original-350x200.gif)
Punctuated equilibrium (4 of 8) No preservation
No preservation: No fossils representing transitional forms are preserved because of their relatively small population size, the rapid pace of change, and their isolated location.![](https://evolution.berkeley.edu/wp-content/uploads/2021/10/2510_evo_resources_resource_image_239_original-350x200.gif)
Punctuated equilibrium (5 of 8) Reintroduction
Reintroduction: Sea levels rise, reuniting the isolated mollusks with their sister lineage.![](https://evolution.berkeley.edu/wp-content/uploads/2021/10/47380_evo_resources_resource_image_240_original-350x200.gif)
Punctuated equilibrium (6 of 8) Expansion and stasis
Expansion and stasis: The isolated population expands into its past range. Larger population size and a stable environment make evolutionary change less likely. The formerly isolated branch of the mollusk…![](https://evolution.berkeley.edu/wp-content/uploads/2021/10/45427_evo_resources_resource_image_241_original-350x200.gif)