Expert: John Shea - 1/14/2010

Question
THOUGH CROMAGNON AND NEANDERTHALS WERE IN EARTH ABOUT SAME TIME, WE ARE DEVOLVED FROM CROMAGNON- WHY?  

Answer
Dear Soumaydeep
My Opinion:  We and Neandertals shared a last common ancestory about a half a million years ago.  Since that last common ancestor lived, Neandertal ancestors
dispersed out of Africa and settled in western Eurasia.  Our ancestors stayed in Africa.  Over time, there accumultated genetic differences between Neandertals
and ancestral humans.  Some of these were random mutations, others were related to adaptation (eg. resistance to cold for Neandertals, tolerance for heat for Homo sapiens).
When Neandertals and Homo sapiens bumped into one another, these differences may have made it difficult for them to interbreed.
Between 130,000-75,000 years ago, both species appear to have been in the Near East.  Though their tools, prey animals, and
habitat preferences are essentially identical, we still do not find them in the same place at the same time (same level of same cave).  This suggests that obstacles to their
interacting and interbreeding were probably already in place 130,000 years ago.  There is a similar situation with the Cro-Magnons (early European
Homo sapiens and the late Neandertals in Europe ca. 45,000-25,000 years ago.  You find them in adjacent regions at the same time, but not in the same place
at the same time.  (This is called "parapatry" in biogeograpy.)  To me, this suggests there was some obstacle to them living in the same place at the same time
(resource competition in my opinion), which is obviously an obstacle to interbreeding.  This being said, there are a few European Homo sapiens fossils and ones from the Near
East that (according to other researchers) show morphologies suggesting possible interbreeding between Neandertals and Homo sapiens.  This is not  impossible
(different baboon genera, much less species interbreed today), but neither does it prove any more-recent humans are descended from Neandertals.  The clearest proof of this last
would be finding distinctive Neandertal DNA in living humans.  No one has found this yet.
Sincerely,
John Shea