What I find fascinating about this is that there are various species which have tackled human speech with at least some success (both actively and passively), while, conversely, we are apparently rather bad at participating in their communicative acts (like, imitating utterances in a meaningful way). Is it just for a lack of interest on our side, or are we lacking something else?<p>Edit, regarding "something else": Apparently, we are able to recognize individuals of other primate species by face at a very early age, but lose this ability soon (even before we acquire speech), probably in favor of other social abilities. Which may be an indication for a high degree of intraspecies specialication regarding our communicative abilities.