Comment: 23:55 - 25:29 (01:34)
Source: Annenberg/CPB Resources - Earth Revealed - 11. Evolution Through Time
Keywords: "Stanley Aramic", "Charles Darwin", evolution, fossil, "intermediate species", "punctuated equilibrium", environment
Our transcription: Yet Darwin's model has run into some difficulty.
Darwin was a gradualist, and that is, he thought that evolution proceeded very slowly, and because of that his theory of evolution required a great deal of geological time.
However, when paleontologists carefully examined the fossil record looking for those intermediates that would occur between species, they couldn't find these intermediates.
Most paleontologists blamed lack of intermediates on an incomplete fossil record, but after more careful study there was a realization that these transitional forms simply don't exist.
This brought about the idea of "punctuated equilibrium", that once a species appeared it lasted for a long time unchanged.
Then suddenly, in terms of geological time, a new species appeared.
And there is really very little, if any, evidence of the intermediates.
Today punctuated equilibrium has been added to Darwin's Theory to account for change seen in the fossil record.
Not only can life evolve gradually, but in a world where rapid environmental change sometimes occurs, rapid evolution can also take place.
The history of life over great lengths of time is governed by the need to adapt or die out.
Geology School Keywords