- According to the theory of gradualism, evolution is a gradual, constant, and slow process. A new species gradually diverges as a result of the accumulation of small changes. - Because of the lack of transition fossils, some scientists dispute this theory. Supporters argue that gradual changes may not be recorded in the fossil record. A transition fossil is evidence of extinct life-forms that shows the link between a new species and its parent species.

- The illustration on the left shows why many transition fossils may not have been found. If punctuated equilibrium was the most common mechanism of speciation, the period of rapid change would take place over the course of 50,000 years. In geological time measured in the earth’s layers, 50,000 years is an extremely thin layer, reducing the likelihood of finding transition fossils. The transition fossils found to date, however, appear to support the punctuated equilibrium model of evolution.

The processes shown in the illustration left to right are ____________.

- gradualism and punctuated equilibrium, respectively.

What is punctuated equilibrium?

- A process that describes periods of rapid evolution followed by periods of stability

Why is it difficult to trace speciation through time?

- Transition fossils are hard to find

Why will the debate over gradualism versus punctuated equilibrium not be resolved in the near future?

- Not enough fossil evidence to support either view.

10.5.1 Time Frame for Evolution: Gradualism vs. Punctuated Equilibrium Flashcards by Irina Soloshenko

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10.5.1 Time Frame for Evolution: Gradualism vs. Punctuated Equilibrium Flashcards

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