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.
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.
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 lake exerts new selection pressures on the isolated mollusks. Also, their small population size means that genetic drift influences their evolution. The isolated population undergoes rapid evolutionary change. This is based on the model of peripatric speciation.