The discussion of accent in that dialog is a neat rhetorical trick, but its main premise is false. If you were to examine the heritability of accent using the standard methods of behavioral genetics, it would turn out to be near zero. (Maybe some confounding factors would yield a small spurious heritability, but there's no way you'd get a "highly heritable" result.)
Some of the other cited facts are also dubious or exaggerated. For example, while accent of adults is no longer as perfectly plastic as before adolescence, it's obviously absurd to claim that "nothing that happens after early adolescence makes an impact on it."
(Also, kids' accent can be easily influenced if you can just place them into a peer group with the desired accent. No such simple solution exists for traits that are known to be heritable.)
Also, kids' accent can be easily influenced if you can just place them into a peer group with the desired accent.
AIUI, that's where people's accents are generally set, in school from about six to twelve. (You can self-modify afterwards, but that's where people start.)
Post by fellow LW reader Razib Khan, who many here probably know from the gnxp site or perhaps from his debate with Eliezer.