PUNCTUATED EQUILIBRIUM

==Gradualism== For a long time it was believed that new species developed over very long periods of time by the slow and gradual change of one species into another. If this were true we would expect to see a smooth transition between ancestral species and their descendants in the fossil record. However, fossil records seem to suggest that species often disappear quite rapidly and are replaced by newer species without much evidence of a smooth transition. ==Punctuated Equilibrium:== This theory suggests that evolutionary change is very slow with little or no change occurring for long periods of time, but that this is punctuated (interrupted) with intervals of rapid change. During these periods of rapid change a species diverges into two or more distinct species, rather than one species gradually transforming into another. This relatively rapid divergence is often brought about by some environmental change in which new, unoccupied niches become available. [image:http://i.imgur.com/ip0XsXb.png]