john mackey be don't die. margee kerr research the science and has a new book entitled scream, chilling adventures in the science sphere. the main science as i understand it is our ancestors heard sound, wrestling and may be worried that it was with the wind in one worried that it was a tiger and ran. the one that didn't run didn't get -- give birth to us. margee: exactly. time is done a good job is forming our threat requirements and her sensitivity that could potentially hurt us. so we are very sensitive to startle and very sensitive to things that have historically opposed a lot of harm. john: now the world is much safer so a lot of this quick response to fear isn't useful anymore. >> there are sort of a mismatch because a lot of the things that we are afraid of today are not the same as they were thousands of years ago. we are not very likely to be attacked by a bear. we have got all of these modern amenities that protect us from natural disasters and the weather. john: we live twice as long as we did just