Narrator: This is Science Today. Commercially harvested organisms, such as fish and wildlife, are changing about three times faster than organisms under natural conditions. Those were the findings of a University of California, Santa Cruz study led by Chris Darimont.

Darimont: People typically think of evolution as something that happens  at a glacial pace over thousands of thousands of generations. And one of the things that this study and others like it have shown is that it doesn't take very many generations at all to start to observe these very rapid evolutionary changes.

Narrator: Darimont says a good example of how organisms subject to predation by humans can shift breeding schedules found in the East Coast cod fishery.

Darimont: In only twenty years, we've seen a decline in the mean age of breeding for females that used to be around six years of age. Now, it's about five years of age, so this really rapid and significant change to breeding at younger ages and smaller sizes.

Narrator: For Science Today, I'm Larissa Branin.