I agree that there might be physical traits that make one likely to develop a stutter. But being likely does not mean you are guaranteed to become a stutterer. And its also for a small percentage. If it's not psychological, explain this. A stutterer was talking to a statue. And he was talking fluently, just like talking to a picture on a wall. What the stutterer did not know was that in fact, the statue was a real person. The person was spray painted to look like a bronze statue. I bet if you could fool a stutterer to talk to a person camouflaged or hidden as an object, he would also talk well. If stuttering was a physical neurological problem, then the brain would not be this selective. Why do we have moments when we talk fine, even if it's for a short time?  It can't be only and purely physical, right?