Expert: John Shea - 12/4/2010

Question
Hi,
I recently watched a documentary about the journeys of the
first known homo sapiens to leave Africa who then went on to
populate the rest of the world; the name of the documentary
is 'The Incredible Human Journey'. Really interesting but
was confused by homo erectus evolving to homo sapiens in
China. Is this correct? Also the documentary talks about how
the first homo sapiens to reach Europe met the Neanderthals
before they eventually died out.
My Main questions is this:
If homo sapiens evolved from primates in Africa, does this
mean Neanderthals and Homo Erectus also come from primates
in Africa like us? And are we from the same evolution line
as them? If so, how did the Neanderthals and Homo Erectus'
make it to Europe and China from Africa, if that is where
they first originate.
If you could give some lame term answers, that would
definitely help me to sleep.

Answer
There are some researchers who propose humans (Homo sapiens) evolved locally in many parts of the world by as genes were exchanged among interbreeding human populations.  The Chinese origin theory you saw described is one of those scenarios.  The majority of the evidence now available, points to Homo sapiens having evolved in Africa by around 200,000 years ago and dispersing (migrating to China) between 50,000-100,000 years ago.
We have no direct evidence for encounters between humans and Neandertals.  There have been some recent studies suggesting some living humans have small amounts of DNA traceable to Neandertal ancestors, but this interpretation is controversial.  The such similarities might simply be traceable to our last common ancestor with Neandertals, Homo heidelbergensis, who lived around 500,000 years ago.
The origins of Homo erectus are not clear at the moment.  Fossils of roughly equal age (1.8 million years ago) occur in Africa and in Asia.
Neandertals originated in Europe, probably after 300,000 years ago.  That we know of, there never were Neandertals in China.  There were other hominin species there, but no Neandertals.
I hope this answer help you sleep.  I certainly don't let this stuff keep me up at night!
The documentary "Becoming Human" on PBS Nova is a bit more up-to-date than the program you watched.  For a good introductory level book on this topic check out Peter Andrews and Chris Stringer's (2008?) Complete World of Human Evolution.
Cheers,
John Shea