Characteristics
The difficulty in making any statement on particulars of Proto-Human lies in the time depth involved, which is far beyond what linguists can trace back today (between five and ten millennia in the cases of Indo-European and Afroasiatic). Some linguists (e.g. Ruhlen 1994) claim that this difficulty can be overcome by means of mass comparison and internal reconstruction (cf. Babaev 2008).
The relatively few linguists who have discussed the subject disagree on how much can be known of the ancestor language. A conservative position, taken by Lyle Campbell, is that it would have shared the "design features" of known human languages, such as grammar, defined as "fixed or preferred sequences of linguistic elements", and recursion, defined as "clauses embedded in other clauses", but that beyond this nothing can be known of it (Campbell and Poser 2008:391). Less conservative linguists have advanced proposals on the vocabulary and syntax of the ancestor language. There are no serious current proposals on its grammar and phonology.
Read more about this topic: Proto-Human Language