punctuated equilibrium does not "produce" rapid evolution, It explains rapid evolution (the punctuated part) and equilibrium (the part where life does not change very quickly).
To reduce a complex theory down to a paragraph or two .... The conditions in any particular environment do not always change rapidly. The organisms in that ecosystem will evolve by mostly competing against others of their own kind for very tiny advantages, Over time these advantages get tinier and tinier and the DNA begins to carry a lot of copies of the successful genes, so almost every offspring is a close copy of the parent with only the occasional random mutation to be a possibility for change (remember, most variation is novel combinations of genes and not random changes to genes). This is an equilibrium phase.
Sometimes conditions change faster. This could be due to an event, i.e. a meteor, a chance encounter with an invasive species, or a world wide climate changing event. Many organisms will have such a stable set of genes that they cannot mate their way to a new combination that works, and they go extinct. When one species goes extinct it changes the ecosystem for nearby species either by allowing more to survive by eliminating a predator, or by threatening them by removing a food source. All are interrelated. The organisms are now changing faster, a punctuated phase.
Generally at the end of a punctuated phase the ecosystem is less populated. Many species have died or moved on. This leaves an easier life for the survivers. They spend some time adapting to the remaining or new predators and adapting to exploit the new or remaining food sources. After a few, maby tens of generations, they are fairly well adapted to their ecosystem, and so each species once again competes primarily with other members of their same species and the pace of evolution reverts back to an equilibrium.
Generally the punctuated phases are much shorter in time than the equilibriums. This is because the earth is usually a pretty stable environment. |
