Near the end of the Cold War, the U.S. government received numerous reports from Southeast Asia of chemical weapons being used against democratic insurgents. After investigating, the U.S. accused the Soviets of supplying chemical weapons to the communist governments in the area. Matthew Meselson, a Harvard molecular biologist, reviewed samples of the substance but was unconvinced that what the U.S. government found was a weapon. Meselson traveled to Thailand with Thomas Seeley, a renowned animal behaviorist, to prove that the yellow substance falling from the sky was not a chemical weapon but a natural phenomenon.