Moses is a prophet in Old testament of Bible. He is supposed to have given Ten commandments, for human behavior. There is a belief that he stammered and this is why, when God commanded him to lead Jews out of Egypt, into the promised land- Israel, he was very hesitant. How could he lead people? God made a concession: his younger brother Aron, was made his spokesperson. That is how the story goes..
Three scientists have made a study and wrote a paper in a Neurological journal about this. Read to the very end. This time the joke is on the scientists!