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A. The Relationship between Host and Parasite Helps Drive Evolution

Narrator: This is Science Today. Researchers led by University of California, Berkeley biologist Thomas Cline, recently discovered that a parasite living on the fruit fly can make sterile fruit flies fertile again. Cline says this unexpected interaction between a parasitic bacteria and its fruit fly host has implications for our understanding of fundamental biological processes.

Cline: To find that infection by a bacterium can restore, can counteract the effects of this single nucleotide change in a particular gene, just shows you how little we know really about the kinds of interactions that go on in the real world, and the kinds of factors that are really very important for evolution.

Narrator: Cline explains that the competition between host and parasite leads to biological change.

Cline: Because it's a constant race-the parasite obviously wants to take advantage of the host, and the host obviously doesn't want to be taken advantage of too much, so there's this constant race, and it's true of humans, it's true of every species on Earth, where there's this constant battle of outracing your parasites.

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