10.3 Gene pools and speciation

Gradualism and punctuated equilibrium

There is much debate within evolutionary biology about the rate at which evolution takes place.

One idea, called gradualism, is that gradually accumulating small changes can lead to very large changes over long periods of time. This theory does not fully fit with the fossil record which seems to show periods of very little change followed by mass extinctions and then a very rapid increase in diversity in relatively short periods of time.

An idea that has developed from the failures of gradualism to explain the evidence in the fossil record is punctuated equilibrium. It looks for evidence of great violent changes e.g meteorite collisions, increased volcanic activity, rapid climate change. These changes would then change the natural selective forces to favour rapid change and adaptation until longer periods of equilibrium where natural selection would

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