My own observations indicate that there is a large difference in how fixed human accents are from one person to the next. I suspect it is the same underlying thing that makes some people faster to pick up a new language than others.But it makes sense if young are learning from parents.
Human accents are learned at early age. I was told by a neurophysiologist that 'accent' and language acquisition is largely determined by age 7 or so in humans (granted this was based on research back in mid 70's when I was in university).
Niels