A merger is probably a good idea.  First, the prehistoric man article is terrible.  In fact it shouldn't exist as anything other than a stub.  The term "Prehistoric man" is no longer used by scholars and hasn't been since the 1970's becuase it is androcentric and because there really is no such thing as a group or type of people who are characteristically "prehistoric".  In other words, people in prehistoric societies have no particualar commonalities except a lack of writing.  Prehistory is a rubric used by scholars to differentiate the methods used to study the past, not a type of people.  There is no such thing as a stage of personhood or social development in which a person is a prehistoric man or woman.  For example, the Inca remained a prehistoric people until the Spanish conquest and yet they ruled one of the most impressive empires on earth and still had no writen records (quipa were memory aids, not writing).  In Central America, the prehistoric period starts more than a thousand years earlier.  Further, the term is Eurocentric and based on the notion of progressive stages of "mankind" like the "stone age".  There are people who still use stone tools.  The "ages as stages" concepts have long since been abandoned in the social sciences since they do not apply universally and can not be tied directly to other political and social developments around the world.  So I say Merge the two articles and cut the outdated garbage.