Aristotle thought that laughter is what separates us from the beasts, and that a baby does not have a SOUL, until the moment it laughs for the first time. Historian Barry Sanders, author of Sudden Glory, says that according to Aristotle, this moment of "human ensouling" is supposed to happen when a baby is 40 days old. We follow radio producer Amanda Aronczyk as she tests this theory on her newborn baby. 
Then we go to Bowling Green State University in Ohio, to tickle rats with psychobiologist Dr. Jaak Panksepp. It's his notion that laughter is found all across the animal kindgom. Boom, Aristotle! Then Dr. Robert Provine, author of Laughter: A Scientific Investigation, shows us chimps who seem to be laughing. Boom Boom!
We also get the giggles with a bit of archival tape from comedians Elaine May and Mike Nichols. And Tyler Stillman, a psychologist at Florida State University, eloquently delineates the awesomeness of laughter.
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