Just a quick comment on this thread, to which several have contributed comments, under "evolutionary changes". I support the concept of changes in the individual due to her/his use of the mouth, including early feeding or the effects of compensatory tongue and jaw movements to cope with a congenital anomaly. . Evolutionary changes would take many,many generations. While there are mechanisms for genetic changes in a short time frame, they are particular circumstances and this would seem not to be one of them. 
On short-term changes, Heather mentions being able to identify accents or languages watching speakers on television, with the  sound turned down. My linguistics lecturer told us that, although she didn't have a study to cite, she had noticed over the years that people held their mouths, in respose, in a way that was ready to use the sounds of the language usually spoken. After that, I started observing young people, at a time when there was an influx of students from China and Taiwan. I've done thisformany years.  I found I  could identify the young people who were newly arrived and used little English, those who had been educated here and used English a lot, and those who used English as the home language. Body language made it possible to refine some of my guesses to regions.
In Australia, older Queenslanders tend to hold their mouths a particular way in repose. I Haven't checked this against younger people.
Interesting, but a bit off topic - other than to note that the children of people who have spoken one language for generations, and hold their mouths and faces ready top speak it, may use their oral/facial structures differently when a different language becomes the home language. That is, it  seems to apply to the individual.
Virginia
in Brisbane, Queensland,Australia
> 
> >The way we use our bodies affects how they look. I noticed long ago 
> that
> >speakers of US English have less developed oral musculature than do
> >speakers of French or Norwegian or Swedish or German or any other 
> language
> >that has hyper-rounded vowels. We use our lips, cheeks and tongues much
> >more over here because we need to distinguish between at least a dozen
> >diferent specific vowel sounds. In US English you can speak  correctly 
> with
> >a much more relaxed face :-) When you are alerted to this feature it is
> >impossible NOT to notice it.
> 
> 
> I have seen this and it is possible to guess at the accent/language 
> of someone speaking on TV, with the sound down.
> 
> I *know* that breastfeeding (and subsequent diet) affects dental 
> alignment, facial and oral structure, and consequent 
> functioning.....no argument there!
> 
> Heather Welford Neil
> 
> NCT bfc, tutor, UK
> -- 
> 
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>

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