Genetics or inheritance
Here we are talking about the characteristics that the person is born with. Sometimes we read about "nature versus nurture", the crossing point between what is inherited and the environment within which we are brought up.
For example, it can sometimes be quite easy to guess where eye colour or height came from with our own parents and grandparents. It is not so easy to explain personality traits, although you do hear people saying "stubborn, just like his grandad"! Character is probably a mixture of both "nature" and "nurture".
Stammering also seems to be a mixture of both nature and nurture. For some there is a definite genetic link, a blood relative who has had or still has a stammer. It is becoming clearer that many children do inherit a vulnerability to stammering. At the Michael Palin Centre more than half of the children we see have a blood relative who has either stammered in the past or continues to stammer. While researchers are trying to find out more about the genetic links, it will be many years before the picture is fully understood - or whether this will help us to decide which therapy is best for a particular child.
The brain and nervous system
However the research is also beginning to suggest (and this may be linked to genetics) that stammering may be a sign that the child's developing nervous system for speaking fluently may be wired differently. The complex systems of speaking – pronunciation, choosing the right words, constructing sentences - all require an extraordinary amount of brain activity and in some of us this seems to happen differently, which can result in stammering. However, the wiring in our brains is ‘plastic” and can ‘re-wire’ over time and with therapy.
Boys are more vulnerable - we don't know why, but boys are more at risk of other speech, language and literacy problems too.
Oral motor skills
This is related to the planning and co-ordination of the movements of articulation - tongue, jaw, voice box, etc. Some research studies have shown differences in the oral skills of some people who stammer - these may be slower or less well co-ordinated, but are so slight that they are imperceptible without scientific measuring equipment.