I am skeptical about Proto-World, but it is not a crackpot theory.
Matt Ruhlen and Joshua Greenberg believe in it. Joshua Greenberg thinks
that there was a small group of humans who came out of northeast Africa
around 50,000 BC, populated the whole world and wiped out all traces of
all other hominids such as Neanderthal. I think it is looney too, but it
is respectable in academic circles. Pat Ryan's analysis of ancient
languages such as Etruscan, Egyptian and Urartian and their possible
relations is quite good. Matt Ruhlen makes a good case for Proto-World.
Prehistory seems to show an entirely different picture, though. If
there was a Proto-World language, it must have been from a group of
peope who spread out and replaced all other languages. Respectable
academics have talked about a "language mutation" around 50,000 years
ago. I think they are wrong about that.
I follow Ruhlen back in time at least as far as Dene-Caucasian.
The most recent "explosion" was Indo-European. Indo-European was just
one branch of Nostratic, which was an earlier explosion. Nostratic may
have been a branch of Dene-Caucasian. This explosion sent languages all
the way to Arizona; Navaho is a Dene-Caucasian language. Cavalli-Sforza
believes that Amerind is associated with Nostratic. I think he is
wrong, but he is more respected than some of us are. I have looked at
languages like Zulu and Hawaiian. There seem to be similiarities that
go beyond chance.
It is a mystery how they could have come about, though.
I don't want to get off the topic of this forum. Issues involving
non-Indoeuropean languages are discussed at
http://www.delphi.com/paleolinguistic
Prehistory is discussed at
http://www.delphi.com/prehistory
The development of the brain and speech is discussed at
http://www.delphi.com/paleoneurology1