"Why do adults find it so hard to learn how to pronounce new word sounds? ... I suspect this parituclar disability is caused, more or less directly, by a genetically programmed mechanism that disables our ability to learn to make new connections in or between the agents we use to represent speech sounds."
NB: This amounts to a version of a "special biology" view of critical periods, which is common in the literature. However, it raises some other important issues -- in particular, what is the specific link between biology and agency?