This was posted on msnbc.com under an article explaining why people jumped off the twin towers.
Years ago, Frederick says, a colleague of his set up an experiment where he subjected laboratory animals to excruciating pain. They could go into another chamber to escape the pain, but if they did they would get their heads chopped off. Other lab animals were allowed to observe this, so they knew what would happen. They they, too, were placed in the pain chamber. They leaped out of it, into the killing one."The urge to escape the pain," said Frederick, "overrode everything else."