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C. Fish Evolve Longer Lifespan by Evolving a Longer Reproduction Period

Narrator: This is Science Today. Guppies living in environments with a large number of predators live longer than those in low-predation areas because they evolved a longer reproductive period. Biologist David Reznick of the University of California , Riverside says their study of the small freshwater fish supports a hypothesis that natural selection introduces changes in only a specific segment of an organism's lifespan.

Reznick: So, all of the increase in lifespan was strictly in the reproductive lifespan and that's consistent with theory because what natural selection predicts is that it only can act on the part of the lifespan of the animal that can contribute to fitness that can contribute to the production of offspring.

Narrator: The researchers then found that the post-reproductive lifespan was the same for guppies in both high and low-predation environments.

Reznick: So, what this tells us is that the guppies do, in a sense, what we predict. We would predict that there would be no differences among these populations in the post-reproductive lifespan because that part of the lifespan has nothing to do with fitness.

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