Gradualism

Gradualism suggests that change is gradual with the accumulation of unique morphological adaptation.

Punctuated Equilibrium suggests that rapid change occurs, with a new species “erupting” from the ancestral lineage and then staying the same

thereafter.

m The evolution of new species by gradual accumulation

of small genetic changes over long periods of time

Slow and steady change in an organism

Over a short period of time it is hard to notice

m Current living zebras (top), extinct quaggas (bottom)

m Stable periods of no change (genetic equilibrium)

interrupted by rapid changes involving many different lines of descent

Rare, rapid events of branching speciation

m Horseshoe crabs have changed little

since their first appearance in the fossil record.

They are in a state of equilibrium

Similar to gradualism

Similar to punctuated evolution

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