http://www.pnas.org/content/102/14/5297.full

Which shows that there is a window of time, that if infants are exposed to monkey faces, that their ability to discriminate between the faces of different individual monkeys is enhanced. This pretty strongly indicates that there is plasticity in face recognition (and presumably communication mediated by facial expressions).

For a communication mechanism to be “innate”, the internal mental representation of the mental state being communicated must be “innate” also. If the internal representation of the mental state is learned, then mechanisms to communicate that mental state must be learned also because it must have a one-to-one correspondence with the internal mental state and can only develop after the neuroanatomy that supports the internal mental state develops.

I remember reading (years ago) about a study that measured the reaction of western and eastern subjects to sexually explicit and/or violent images. Essentially the subjects were put in a room and given some very strong hard-core porn to watch. Some people were told they were being observed while they watched, others that they were unobserved. In both groups the westerners tended to react with the same facial expressions (ie they behaved the same if they thought they were being observed or not) – mostly betraying distaste. In contrast, the easterners (Japanese, I think) exhibited the same facial expressions of distaste as the westerners if they thought they were unobserved, but if they were in an ‘observed’ group most of them put on tight grins and did a lot of vigorous head nodding. To western eyes the ‘observed easterners’ looked like they were really enjoying their porn-fest, wheras the opposite was true.