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C. Putting Evolution to the Test

Narrator: This is Science Today. About 300 million years ago, there was one and a half times more oxygen in the atmosphere than there is now. The thick rich air permitted the evolution of dragonflies the size of seagulls. Twenty or 30 million years later, in what scientists call the Permian period, the oxygen level plummeted and the huge insects went extinct. Biologist Jeff Graham of the University of California, San Diego says that's no coincidence.

Graham: If you think about an animal that might have evolved because of the presence of large quantities of oxygen in the atmosphere, well, if you pull that oxygen out of the atmosphere, the effect might well have been to drive them to extinction.

Narrator: You can't go back and prove that theory, but Graham says you can test it. Breed insects at, say, ten thousand feet, where the air is thinner.

Graham: And there one can effect -- naturally -- changes in the atmospheric oxygen which would have been very analogous to the kinds of conditions that were coming on in the Permian with respect to atmospheric oxygen levels.

Narrator: If generations of insects change size in proportion to oxygen, it would provide a brief glimpse of how evolution works over millions of years. For Science Today, I'm Steve Tokar.