Sunday, October 03, 2010

Genetics, developmental, and environmental

Judy's ISAD13 also has a forum called "Ask the prof", and I was part of that once. But I was not asked again... ;-) She might have thought that I was a professional or others complained that I was not a professional. So now the level is higher again. I am just not good enough to give vague fuzzy feel-goody answers. No-one has answered genetics questions yet. I guess Dennis Drayna didn't have the time yet. So let me answer one of them here.
In about 50% cases of PDS, genetic connection is found. Is it true? For the rest, is it safe to assume that their stammering is the outcome of environmental factors (early negative speech experiences and learned response to that)? Thanks in advance!
This is a common misconception, even among most SLTs. If 50% is genetic, then the rest is non-genetic. Most geneticists call non-genetic environmental, but this is highly misleading for the non-expert mind. A better wording is to talk about developmental factors and socio-environmental factors. Developmental is mainly the process by which the fertilized egg is developing to an adult human being. The key phase is up to age 5. Developmental issues can arise due to allergy, malnutrition, random incidents like hitting your head, and illnesses like virus infections. In the strict sense they are of course environmentally driven, but it's more about a healthy environment needed by the body to build itself. What most people mean by environment is the social environment of the child. So it's wrong to say that 50% is due to social environment. This number is very likely low, maybe 10-20%. And 30%-40% is due to developmental issues.

That is often what the blank slaters (i.e. we are born equal) think. X (intelligence, personality, stuttering) might be 50% genetic, but we are so eager to point out that 50% is environmental, i.e. societal. But of course, they got it completely wrong. Most of the environment consists of neurobiological development. So the society, e.g. parents, schools, and social interactions, is at best 10%-20% in many cases.

4 comments:

sachin said...

Thanks Tom, for answering my question! Few academics know how to communicate with lay person. That is why guys like you should be on that panel! I think.
sachin (TISA)

Ora said...

"I was part of that once. But I was not asked again... ;-)"

Well, at least you're being quoted by the experts! See http://www.mnsu.edu/comdis/isad13/papers/reitzes13.html

Pam said...

Tom, Have you asked Judy if you can be part of the ask the professionals section? Do you have to be an academic professor to be part of the panel?

Ora said...

Actually, it looks like anyone can post in that section. I see at least one response, where the responder is not part of the panel (Nan Ratner). Also, it's possible for anyone to comment on responses. So presumably, Tom, you should feel free to add your comments as well.