There's not just one cause. There are many.
Physical/biological factors would be:
Family history of stammering in blood relatives
The organisation of the brain for speaking
The co-ordination of the speech mechanism
Environmental causes - past and present
Rapid pace of life - lots of commitments, activities and demands
Everyone speaking quickly
Everyone talking at once
Expectation to speak up - whenever
Personality Causes - the sort of person you are can make a difference
Perfectionist (or self-critical)
All of these factors can cause people to stammer. And there's probably more.
"T-t-t-today junior!" -Billy Madison.
I don't know what causes stammer.
I know it's curable : )
The mind thinking faster that the mind can form the spoken idea in words thru speech.
I heard you can get it if your forced to write right handed & your really a left hander. I've not seen the film The Kings Speech but I have seen a documentary about this and it mentions it there
Smashing your head against your toys when you were a child
"yuuuuuppppppppp * * in slow voice
Have your parents take you to a speech therapist.
Yes, 'parent', sorry.